# Specific 3D Printers, Scanners, & Hardware > Peachy Printer Forum >  Z axis calibration idea

## Aztecphoenix

I was thinking about building a variable resistor using coiled copper wire and a float to determine the water level, and by offsetting multiple coils could give you better resolution.

any suggestions would be greatly welcome

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## Pete

Sounds like you're aiming for real time feedback rather than a calibration aide. For your idea I think static friction between the float and coil is going to be an issue, you might find you get jumps rather than a continuous change. For real time sensing then solid state wins it for me, I'm thinking guage pressure or capacitive ATM.

The idea of a calibration aide might be good though. For drip calibration you set a rate and let it count for a given rise in liqiud, then you can put in a drips per mm number. This may take some time and the more level you measure the better the result will be as you minimize errors. You could make a circuit board with a more accurate smaller gap which would take calibration time right down but hopefully maintain accuracy, this is as simple as a few transisistors and a cheap circuit board with some LEDs.

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## mike_biddell

Having a think about  this............. how about a finely graduated scale on the side of the  tank (printed and laminated) and an optical mouse chip on a float. The chip returns changes in Y as it floats up the scale. This is a robust solution, which could have amazing accuracy. Plus, dirt cheap. 

They have a resolution from 300 dpi up to at least 800 dpi. So about 3 thou up to just over 1 thou.......... that shud be plenty.

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## Feign

An alternate and simpler auto calibrator would be a pair of wires with gaps that both go into the microphone like so:

Tone generator (speaker)_____ ____Mic in
Drip Sensor__________________ _|

Such that the spacing between the lower and upper gap is exactly a centimeter (or whatever unit the Peachy uses for calibration).  Then run just saline through the dripper without any resin.  The software won't start counting drips until the level reaches the first wire and have the software automatically stop the count when it hears the tone coming through the second wire.  Suddenly, you know exactly how many drips are between the first and second gap!

It would probably be good to run multiple calibration measurements with it at different heights on the tank wall to be sure, so that you get a good average fill rate per drip.

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## Aztecphoenix

> Having a think about  this............. how about a finely graduated scale on the side of the  tank (printed and laminated) and an optical mouse chip on a float. The chip returns changes in Y as it floats up the scale. This is a robust solution, which could have amazing accuracy. Plus, dirt cheap. 
> 
> They have a resolution from 300 dpi up to at least 800 dpi. So about 3 thou up to just over 1 thou.......... that shud be plenty.


love that idea, though a fine enough scale might be the only problem, definitely something to look into.

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## mike_biddell

@Atztecphoenix - there shouldn't be a problem with the scale. Even an old Laserjet 4000 can print at 600 DPI. The mouse chip can resolve movement at 800 dpi on any surface (apart from very reflective) using very clever digital signal processing, so the scale is almost immaterial. You could just chose a surface with a fine texture and use that. All that for a £1 or so (English money). But just gutting an optical mouse, and putting it in an IP65 box would work. http://pickandplace.wordpress.com/20...optical-mouse/

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## nka

or what about Ultrasonic Proximity Sensors?

Is the precision good for that?

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## Chayat

> or what about Ultrasonic Proximity Sensors?


I was thinking this too, maybe having 1 in each corner and then taking an average? I dont think the precision will be good enough though.

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## Aztecphoenix

> @Atztecphoenix - there shouldn't be a problem with the scale. Even an old Laserjet 4000 can print at 600 DPI. The mouse chip can resolve movement at 800 dpi on any surface (apart from very reflective) using very clever digital signal processing, so the scale is almost immaterial. You could just chose a surface with a fine texture and use that. All that for a £1 or so (English money). But just gutting an optical mouse, and putting it in an IP65 box would work. http://pickandplace.wordpress.com/20...optical-mouse/


so now the only question is how to interface it with the Peachy Printer, (or for that matter, how to interface anything with the Peachy Printer, I still can't figure out how we could do that unless it all has to be done through the connected computer)

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## mike_biddell

It can interface with the standard peachy using a picaxe chip, which reads the y output and pulses the mic input of the Peachy as if it was a drip. But an absolutely accurate drip.

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## nka

as mike said... you only need to generate a drip pulse. Not too hard to do (in fact, just touching the 2 cables).

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## Feign

> It can interface with the standard peachy using a picaxe chip, which reads the y output and pulses the mic input of the Peachy as if it was a drip. But an absolutely accurate drip.


I would not have thought of that, very simple way of doing it.  How do you figure mounting the sensor so that it doesn't drift away from or stick against the side of the container/scale?

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## mike_biddell

Mount the peachy printer on a float and the mouse chip. A reasonably tight fit in the tank.

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## Aztecphoenix

> It can interface with the standard peachy using a picaxe chip, which reads the y output and pulses the mic input of the Peachy as if it was a drip. But an absolutely accurate drip.


since I'm a complete noob when it comes to microproccesers, can you elaborate more?

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## mike_biddell

yeah...... u can create your own chips using visual basic and picaxe chips. I am a big fan. You then programme them using a laptop and a serial link cable. They can do anything you tell them to. Very very easy to use. You would soon get into it. The dev/programming software is also free:- 
http://www.picaxe.com/Software/PICAX...amming-Editor/

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## mike_biddell

We can go completely closed loop Z control, by having the same picaxe chip turn a pump like the one Pete suggested ON and OFF. So the Picaxe could turn the pump ON and quickly allow 2 thou of fluid into the tank, send the drip pulse to the mic input, then turn OFF and harden that layer, then ON again and so forth. All using the basic Peachy.

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## nka

I'm working on something like that. Except, I wont be using a pump but a solenoid valve. Just waiting to see if the noise is acceptable (on/off each drip). Else, would take a variable valve, but they are not cheap.

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## Aztecphoenix

> I'm working on something like that. Except, I wont be using a pump but a solenoid valve. Just waiting to see if the noise is acceptable (on/off each drip). Else, would take a variable valve, but they are not cheap.


you might find it more acurate to use both, since water drop vary in sizeplacing a solonoid valve right at the end of your input tube to stop all water flowthe instand the desired level is reached would giv you far more accuracy, but in all I like where this train of thought is going, I'm looking into getting a PICAXE setup when I can get enough money together (currently laid off)

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## Pete

I'm working on a solution for a pump with a standard peachy (I'm gonna upgrade my'n to USB so I'll have whatever control and feedback I want!). For the moment it will consist of circuitry so that you can feedback into audio and use the stock software. This does mean that the drips become mega size so the 'drips' will probably need be quite slow but because they're larger it shouldn't compromise the printing speed. For extra control, USB is the way forward (I'm convinced of it) once I get up and running with the standard, USB and the pump will be my first major hacks so I'll be sure to post the results.
When I get a moment I'll splash down a circuit diagram and a partslist so you could get started building if you like. I'm hoping that everything will be achievable with moderate soldering skill, all through hole components and some stripboard.

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## nka

Pete, in other word, you're builing the "Pro" Peachy" :P

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## Aztecphoenix

this got me thinking, if we can get real time feedback for the Z axis, what if we used a laser rangefinder type system to identify how far the print head is from the base of your build area and then by adding small photosensors, one at each corner and one in the middle of your build area, in theory wouldn't we be able to make the Peachy "self calibrating"?

so, the laser would shine and the range finder would count how long the light takes to reach it, then the laser would scan to find the center photosensor establishing that as zero, it would then move to each corner measuring it's travel distance on the X and Y, after locating the corner it would return to center and repeat for the other three corners, it could then take those measurements to determine the X and Y build area and by having the real time Z axis feedback calculating the entire build volume would no longer be required and the machine would be able to calibrate itself prior to each build.

the main reason I am looking into this is I plan to use different sized build resivoirs for different prints ( no need to use a three cubic foot resivoir for a print that only takes up five cubic inches)

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## harpo99999

unfortunatley the speed of light vs speed of electricity in wires is light is several times faster, partly due to the resistance of the wire, so using the laser to calibrate the distance would not be effective or reliable

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## Aztecphoenix

> unfortunatley the speed of light vs speed of electricity in wires is light is several times faster, partly due to the resistance of the wire, so using the laser to calibrate the distance would not be effective or reliable


some kind of range finder be it laser or sonic, I'm more curious about the feasibility of the overall concept

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## Anuvin

Well sure it's possible to use a laser rangefinder. The code's in python, open and easy to learn and change. Problem is that I don't think you can get either method of detection and still get a printer out for under $100.

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## Aztecphoenix

> Well sure it's possible to use a laser rangefinder. The code's in python, open and easy to learn and change. Problem is that I don't think you can get either method of detection and still get a printer out for under $100.


I'm just talking about after market mods, if they want they can add it to the pro version for a slightly higher pricetag (you pay more for the pro as it is)

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## mike_biddell

Refining the optical mouse idea, it is much simpler to use a strip of textured plastic about 1/2 inches wide,  1/10 inch thick and an appropriate length. Attach this to a small polystyrene float. Mount the mouse circuitry in a static position at the top of the tank, so that the float strip moves paste the mouse window (feed the strip thru a slot by the mouse read window), as the depth in the tank increases. This would definitely work and give excellent Z resolution at a very cheap price.

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## Aztecphoenix

> Refining the optical mouse idea, it is much simpler to use a strip of textured plastic about 1/2 inches wide,  1/10 inch thick and an appropriate length. Attach this to a small polystyrene float. Mount the mouse circuitry in a static position at the top of the tank, so that the float strip moves paste the mouse window (feed the strip thru a slot by the mouse read window), as the depth in the tank increases. This would definitely work and give excellent Z resolution at a very cheap price.


the only downside is you have to have as much clear space above your build reservoir as the actual depth of the reservoir so the gauge can have full travel.

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## mike_biddell

not necessarily..... u cud have the upper tank offset by 1 inch or so and have a scale slot on the side of that too !!!!

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## Aztecphoenix

on further reflection,  a separate tank off to the side of the whole machine attached with an umbilical to the build tank, that way the water would displace both at an equal rate, it just might work. 

this setup could also be used as an overflow cut off switch, the gauge has a contact on top and an adjustable slide with the second contact, this way as the gauge floats up when the top reaches the slide it can activate a solenoid valve to stop the drip flow.

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## Anuvin

This thread is super awesome. I hope someone tries this and reports back!

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## BumpingSpheda

I apologize if these questions are redundant, but how many "dots per inch" is required for proper z-axis resolution of a general purpose 3-D printer? And assuming our z-axis measuring equipment was capable of measuring in increments that were infinitely small, at what point does the argument become moot because the laser's field of view in our Peachys (or perhaps the behavior of the MakerJuice in relation to the laser that we're using) can't keep up with the performance level? In other words, I guess, what's the lowest resolution that everyone would be okay with?

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## Feign

The resolution of the Peachy is a tricky thing, because it's analog rather than digital.  It has a measurable precision, but that can change drastically based on the software (which is still changing quite a bit) and the clarity of the sound card used.  Possibly even the quality and shielding of the cable, being able to actually _see_ sound quality as a physical object can really turn someone into an audiophile.  :Stick Out Tongue: 

Also, the laser currently has to be calibrated by eye, meaning the overall scale would be hard to get better than +-.5mm, but details smaller than that would still show up if you have the sound quality for it.

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## mike_biddell

As an example, the Form1 3D printer can resolve Z to .001 inches. There is no reason why Peachy can not match that as the two use very similar technology. I think the Peachy hardware seems excellent. The only question mark for me relates to the Z axis calibration in terms of drip control and the software corrections for each Z layer. The beta prints so far all appear to have Z dimension problems, hence this thread to identify a way of doing closed loop Z with a basic Peachy.

I meant to add that the chip used in digital vernier calipers looks very interesting. http://www.ebay.co.uk/itm/6-Digital-...item2ec3149f37

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## Aztecphoenix

> I apologize if these questions are redundant, but how many "dots per inch" is required for proper z-axis resolution of a general purpose 3-D printer? And assuming our z-axis measuring equipment was capable of measuring in increments that were infinitely small, at what point does the argument become moot because the laser's field of view in our Peachys (or perhaps the behavior of the MakerJuice in relation to the laser that we're using) can't keep up with the performance level? In other words, I guess, what's the lowest resolution that everyone would be okay with?


in a sense, the argumant is moot,
as  get better with our calibrations and others develop ways of fine tuning the laser and mirrors we would be able to get finer and finer resolutions possibly even the the point of nano. the whole purpose of this thread is to try and make the Peachy the most reliable 3D printer on the market even if everything we are talking about is to be done after market. to be able for the printer to accurately know what its current Z height is simply means you get that much more precise of a final product with less fussing around.

3D printing technology is constantly advancing, and there is no law that states that it has to advance in a certain order, if we can measure more accurately than our printer can print it just gives us an excuse to make the printer more accurate to match.

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## mike_biddell

An interesting article on reading data from digital calipers http://www.instructables.com/id/Read...n-Arduino-USB/

Could we get a float to turn the caliper mechanicals?

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## mike_biddell

Just had a fiddle about with my digital calipers and I am really warming to the idea. I can open them fully and zero them (do this at the start of the print). As you close them, the reading increases as expected but with a negative sign (so just get picaxe/arduino to ignore the sign). The caliper is a bit stiff and would need loosening up, but not sure whether this would affect the capacitance. The Z value is easy to read with a PIC chip and you can simply look at the display to get current Z height (ignoring the sign). The resolution required could be set using dip switches (say 8), which would give 256 combinations of vertical res. The PIC just reads the dip switch pattern to get the required Z res. The PIC simply then turns on a solenoid or pump until required Z reached then pulses the mic and turns pump/solenoid OFF. Then delay to allow hardening then pump on again.

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## mike_biddell

I've just splashed out on these calipers..... will report back to see if I can loosen them enough to be float operated. These can resolve to 10 thou. They operate off capacitance ............. will report back when I've had a go. http://www.ebay.co.uk/itm/4006804750...84.m1439.l2649

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## nka

love the idea... wonder if they are good, I would buy some for personnal use! :P

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## mike_biddell

sebastian.... they are very useful for general  purpose use...... will let you know how my experiments progress.

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## jstrack2

I don't know if this has already been discussed, but what about using a Kalman filter (which is just something to be implemented in software) to make use of the information from the drip and whatever is used to accurately measure the present liquid level (such as the caliper)? This way the caliper (or whatever equivalent used) would give it good accuracy, and the individual drips would give it amazing resolution.

For example say each drip adds 0.001 mm. Then even if the caliper had poor resolution the Kalman filter would just "trust" the drip in the short run giving .001 mm resolution, and then use the caliper data to prevent it from drifting after several drops. So with this system you would still have to do a test calibration of the drip system to understand roughly how many drips it takes to go up a given height, but then after that it would have great accuracy and awesome resolution. The accuracy would be as good as the caliper and the resolution as good as the drips.

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## Anuvin

Isn't that pretty much how it works now? The software lets you put in how many drips it takes to fill the container, and then the software counts the drips, and estimates the Z. What would the caliper do, in your suggestion? Are you suggesting that the software compare the Z based on caliper data to the estimated z based on drip count?

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## jstrack2

Yes the software would compare the two values, and with each drip comes up with a new estimate on the position. Without the caliper (or something comparable, although I really like the caliper idea!), just counting drips obviously leads to significant inaccuracies. Only using a caliper can limit the resolution. By using the Kalman filtering method you get the caliper accuracy and drip resolution. And this level of detail of position will be known with each drop. The Kalman filter is pretty great. It produces the statistically optimal estimate of the system state. For example it is used to determine the state of charge of a battery, and it is used with accelerators and gyroscopes in a phone to give accurate orientation readings. It would be sooo awesome for the Peachy Printer to be super accurate and have extraordinary resolution in the z-axis! Plus I think this would be pretty robust too.

http://en.wikipedia.org/wiki/Kalman_filter

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## mike_biddell

I like the Kalman filter Idea. I once use such a filter for a navigational invention.....very effective. We could start with a basic drip calibration (an expectation about what a drip is worth in Z terms) and every 0.1 mm, redatum that calibration. So in other words, the picaxe would receive the drip pulse (not the Peachy) and the Picaxe would put out the rationalised pulses on the basis of the accurate drip value.

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## jstrack2

Yeah I think this will work well. One detail (although this matters relatively little since it is a small fraction of 0.1 mm) is that I think that the calculation should be redone each drip. If it is calculated every 0.1 mm and otherwise each drip just adds a fixed amount then there will be a correcting jump every 0.1 mm, rather than a more smooth fix every drop. Again though this doesn't really matter much. With decent initial drip calibration I doubt this effect will be noticeable. Getting this right will make the printer slightly more robust.

Anyway I am real interested in hearing updates about how the caliper idea works for you. I was pretty surprised how cheap they are.

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## Anuvin

Ah, I understand now, thanks for explaining. That does make sense. Calipers are generally inexpensive, so this could really wind up awesome and cheap. 

Call me an optimist, but I think that the baseline Peachy setup will end up being adequate for most users. I have been getting to get very consistent numbers with a cheap burette tip. http://labsuppliesusa.com/burette-tip-3e3620-each/ I only mention this for anyone reading the thread who is concerned that the provided kit won't be adequate. 

I can't wait to see what comes out of this thread. Mike, be sure to keep us updated.

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## jstrack2

Yeah that's a good idea. If the drop size is consistent and the caliper & drip Kalman filter system is implemented then even if the drip rate varies the z position will still be known with extreme resolution and accuracy.

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## jstrack2

Of course as long as the drip size doesn't vary too crazily the Kalman filter will also clean that up nicely.

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## BumpingSpheda

> in a sense, the argumant is moot,
> as  get better with our calibrations and others develop ways of fine tuning the laser and mirrors we would be able to get finer and finer resolutions possibly even the the point of nano. the whole purpose of this thread is to try and make the Peachy the most reliable 3D printer on the market even if everything we are talking about is to be done after market. to be able for the printer to accurately know what its current Z height is simply means you get that much more precise of a final product with less fussing around.
> 
> 3D printing technology is constantly advancing, and there is no law that states that it has to advance in a certain order, if we can measure more accurately than our printer can print it just gives us an excuse to make the printer more accurate to match.


Badass.

What about something like a potentiometric transducer linked up to a tone generator? You have your float device, it's in between and closes the gap between two vertical traces, one of which is Copper (or some material with very low resistance), the other a different material/form factor with a known/calibrated resistance per unit of distance. The measured voltage determines the height of the float which is converted to a frequency that the tone generator can push to the mic-in.

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## jstrack2

I think that a potentiometric transducer would work as well. It might be easier than the caliper I think. I would prefer the caliper though all things being equal since I think it would be more precise and more importantly much more accurate. A weakness of the caliper's approach is it takes a relatively long time to make measurements. But this is irrelevant for the Peachy Printer, since the liquid level shouldn't rise to the top in a second or two! haha

As for sending the signal to the computer I think maybe the voltage could be just directly sent to the computer via the headphone jack just like the drip does. If using the caliper a microcontroller would probably be needed, such as a PIC. Some microcontrollers can be bought for only a dollar or two though so I don't think this rules calipers out. It's nice that there are multiple options!

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## jstrack2

Also adding a microcontroller should be pretty easy since the Peachy already has a circuit.

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## Aztecphoenix

> I think that a potentiometric transducer would work as well. It might be easier than the caliper I think. I would prefer the caliper though all things being equal since I think it would be more precise and more importantly much more accurate. A weakness of the caliper's approach is it takes a relatively long time to make measurements. But this is irrelevant for the Peachy Printer, since the liquid level shouldn't rise to the top in a second or two! haha
> 
> As for sending the signal to the computer I think maybe the voltage could be just directly sent to the computer via the headphone jack just like the drip does. If using the caliper a microcontroller would probably be needed, such as a PIC. Some microcontrollers can be bought for only a dollar or two though so I don't think this rules calipers out. It's nice that there are multiple options!



this is essentialy what my original suggestion was before it evolved into the discussion we are currently at.

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## mike_biddell

How much does the potentiometric transducer cost. Where can you buy it from and mechanically how do you set it up? We could try it !!!!! What would be the potential Z axis resolution?

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## EthanSpitz

Is the liquid we are dripping in to the container conductive? I.E. is it saltwater? If it is, we could make long resistive strips and line the container with them and measure the resistance across it. As the water level rises, current will go through less of the resistive material and will cut across the liquid to the other side reducing the resistance in real time as the liquid level rises. It could be configured as a voltage divider and output pure analog values that could be scaled to z height.

You could use that instead of the float idea for measuring the height. I personally don't like the idea of a float as there is a mechanical element to the sensor that will rely on friction among the edge of the container or whatever your float is sliding against.

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## Aztecphoenix

> Is the liquid we are dripping in to the container conductive? I.E. is it saltwater? If it is, we could make long resistive strips and line the container with them and measure the resistance across it. As the water level rises, current will go through less of the resistive material and will cut across the liquid to the other side reducing the resistance in real time as the liquid level rises. It could be configured as a voltage divider and output pure analog values that could be scaled to z height.
> 
> You could use that instead of the float idea for measuring the height. I personally don't like the idea of a float as there is a mechanical element to the sensor that will rely on friction among the edge of the container or whatever your float is sliding against.


The only problem with that is you would have to recalibrate the sensor every print unless you can keep the salt level the same for every print which would end up costing more per print because you would have to throw out the water and remix it for every print.

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## EthanSpitz

> The only problem with that is you would have to recalibrate the sensor every print unless you can keep the salt level the same for every print which would end up costing more per print because you would have to throw out the water and remix it for every print.


Can you explain what you mean? When you talk about level, are you talking concentration? You could probably assume a concentration based on the initial value when starting the print.

EDIT:
Also, if you use a relatively high resistance material, the variability or the resistance of the salt water could probably be rendered negligible

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## Feign

A more volatile variable could be the high resistance of the uncured resin floating on top of the saline.  Uncured resin adheres to the side walls of the tank for a little while as it rises, making the blurring effect you see at the bottom of the resin layer in the demonstration videos, it would also adhere to the resistor strips, unpredictably increasing the resistance between the two strips until it is sufficiently washed off by the saline (a distance which also can't cleanly be predicted).

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## EthanSpitz

> A more volatile variable could be the high resistance of the uncured resin floating on top of the saline.  Uncured resin adheres to the side walls of the tank for a little while as it rises, making the blurring effect you see at the bottom of the resin layer in the demonstration videos, it would also adhere to the resistor strips, unpredictably increasing the resistance between the two strips until it is sufficiently washed off by the saline (a distance which also can't cleanly be predicted).


right, but what do we need to know when we make the print, the height of the saline or the height of the resin floating on top. It appears to me we can completely ignore the height of the resin and just take the measurement at the height of the saline.

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## jstrack2

Also in general it is hard to get good accuracy using resistors. So I think that capacitance based circuits (such as the caliper) are preferable.

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## jstrack2

> I personally don't like the idea of a float as there is a mechanical element to the sensor that will rely on friction among the edge of the container or whatever your float is sliding against.


I don't understand what the problem is here. It will take some work to make a simple, cheap and reliable design, but what is so inherently bad about something floating up the side?

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## Nahoj

Would it be possible to use a jewlery scale to find the weight of the upper container, to calculate the volume in stead of meassuring the level in the lower container? You get pretty cheap ones with 0.1g accuracy.....

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## EthanSpitz

> Would it be possible to use a jewlery scale to find the weight of the upper container, to calculate the volume in stead of meassuring the level in the lower container? You get pretty cheap ones with 0.1g accuracy.....


I actually really like this idea....

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## jstrack2

I think the main problem with a jewelry scale is that they generally can't hold much mass (at least the cheaper ones). For example if you had a 1 kg max scale the build volume would be significantly less than 10x10x10 cm. Also the container would need to have totally vertical walls. If it doesn't then things could get way more complicated.

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## EthanSpitz

> I don't understand what the problem is here. It will take some work to make a simple, cheap and reliable design, but what is so inherently bad about something floating up the side?


I think the problem is going to be the reliability/accuracy

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## EthanSpitz

> I think the main problem with a jewelry scale is that they generally can't hold much mass (at least the cheaper ones). For example if you had a 1 kg max scale the build volume would be significantly less than 10x10x10 cm. Also the container would need to have totally vertical walls. If it doesn't then things could get way more complicated.


how does it work with drips right now and height? Doesn't it need to know the shape of the container anyway?

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## jstrack2

Why would it not be accurate? Calipers have extremely good accuracy. I saw on ebay one for only 9 dollars that had 0.02mm accuracy. The one posted was cheaper and had 0.1mm accuracy. Resistors will not achieve that. Plus calipers are much more reliable than using resistance.

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## Feign

> Would it be possible to use a jewlery scale to find the weight of the upper container, to calculate the volume in stead of meassuring the level in the lower container? You get pretty cheap ones with 0.1g accuracy.....


Now that's actually a pretty great idea.  In fact, if you use equal-sized containers for both the top and bottom, then you can use almost all of the ideas in this thread to find the height without any chance of the mechanism coming in contact with the resin.  It would also help with the problem of the optical mouse and digital caliper ideas accidentally registering ripples as layer movement.

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## jstrack2

> how does it work with drips right now and height? Doesn't it need to know the shape of the container anyway?


Yeah you are right. Scratch that point. Still the mass issue exists, but if that can be overcome real cheaply then I think that it could definitely work.

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## Nahoj

There are a lot of different jewlery scales at aliexpress.com.

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## jstrack2

Maybe a scale with less accuracy (like one gram) could hold more. This would still be real accurate and would be simple.

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## jstrack2

For example if the container was just 10 x 10 cm wide then 1 g (~1 cm^3 of the salt water) would add just .1 mm of height. If the container is wider then the accuracy will be even greater. That's like the caliper. The scale has to fit the size of the container which is a drawback since the scale will have to connect to the microcontroller. Work will have to be done to get each different scale size to communicate with the microcontroller properly. 

Of course with the caliper it is limited in height (maybe 150 mm), but the other two dimensions could be unlimited in size.

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## EthanSpitz

> For example if the container was just 10 x 10 cm wide then 1 g (~1 cm^3 of the salt water) would add just .1 mm of height. If the container is wider then the accuracy will be even greater. That's like the caliper. The scale has to fit the size of the container which is a drawback since the scale will have to connect to the microcontroller. Work will have to be done to get each different scale size to communicate with the microcontroller properly. 
> 
> Of course with the caliper it is limited in height (maybe 150 mm), but the other two dimensions could be unlimited in size.


How about instead of just buying a scale, one could buy load sensors that are accurate to the gram, then you can stick any container on top of it.




> Why would it not be accurate? Calipers have extremely good accuracy. I saw on ebay one for only 9 dollars that had 0.02mm accuracy. The one posted was cheaper and had 0.1mm accuracy. Resistors will not achieve that. Plus calipers are much more reliable than using resistance.


How do you plan on attaching a caliper to the water level?

Also, resistance would be plenty reliable. You wouldn't be measuring the resistance of the water, but the resistance in the strip, which will change lengths based on the height of the water.

----------


## Aztecphoenix

Are there actually mechanical components used in the calipers or does it merely measure a difference in capacitance over the length of the slide?

----------


## mike_biddell

the mechanical components keep the etched capacitors in close proximity and allow the scales to be moved relative to each other using a small roller wheel

----------


## EthanSpitz

> the mechanical components keep the etched capacitors in close proximity and allow the scales to be moved relative to each other using a small roller wheel


The challenge would be to build that into a float cheap, but I don't know how you're going to keep them really close without having too much friction on the side of the container

----------


## jstrack2

It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.

I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.

Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).

----------


## EthanSpitz

> It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.
> 
> I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.
> 
> Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).


I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.

----------


## Aztecphoenix

> It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.
> 
> I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.
> 
> Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).


Why use the float to move the slider? use the float to move the scale

----------


## Aztecphoenix

> I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.


depends on what you use as a float, some materials float better than others with less displacement.

----------


## jstrack2

> I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.


The container will have to be pre-filled some, but this shouldn't be too much of an issue.




> Why use the float to move the slider? use the float to move the scale


I was thinking the slider would weigh less, but I think either is okay. Also though the scale will have a wire coming out of it, so moving it may be a bit messy.

----------


## jstrack2

I'm not sure exactly how this would be done, but perhaps using adjustable leverage on the scale could be made where the accuracy and max weight can be varied. So if the filled container is heavy then adjust it so accuracy is say 10 times less but it can hold 10 times more weight. This may be very tricky though.

----------


## jstrack2

Or actually just using a scale and swapping out the load cell when an especially large or small print is desired, but leaving every else might be easier. The rest of the circuitry shouldn't need to be replaced.

I really want to see a high accuracy measurement system used because I think that the prints could be super awesome.

----------


## Feign

To a point, the higher resolution the better, but I mentioned a possible problem earlier that I'll elaborate on.

Because of the top-surface nature of the printing, there will always be ripples in the fluid under your measurement device.  Not just from the dripping action of the top tank into the lower one, but also from natural ground and air vibrations.  A small amount of the time, when you get to within a single drop of a change in the sensor's measuring, the ripples can cause the sensor to 'flicker' between one position and another.  Because there's not a more complex input than a single on/off signal, this flickering might drive the software to think that the print has gone up several layers in one drop.

While it's possible to filter this flickering out, it would require a much more complex circuit than what most are suggesting in this thread.

----------


## jstrack2

I don't know that this is true for some of the methods suggested. For a method using a float small ripples are unlikely to lead to very much movement at all in the float. Ripples can certainly screw up the print, but I don't think that they will cause very much movement of the float. The weighing method should be totally unaffected. Obviously the drop counting method is also unaffected.

Also the direct z-axis measurement methods do not need anywhere near single drop precision. If the drop counting and Kalman filter is used in conjunction with some relatively accurate measurement method then the Peachy will already have single drop resolution. I suppose if single drop _accuracy_ is required then this would be an issue, but I don't think that kind of accuracy it needed for measurements. The whole printer would need to work a lot better to do that. A 25 cm x 20 cm wide container would add just 1 micron per drop. How many people would complain if the print ended up a couple microns or so too short/tall?

----------


## Anuvin

For a $100 printer? A few microns is no big deal.

----------


## Feign

> For a $100 printer? A few microns is no big deal.


True, and I suppose this is something that a lot of us in this thread have lost sight of.

Still, it's fun to daydream about taking a $100 printer and making it into a top-tier machine through addons and mods.

----------


## jstrack2

My point is though that if a pretty good accuracy method is used (like a good scale or caliper) at least from the z-axis measurement side of things you will have top-tier machine print abilities. It will have a micron or so resolution (as far as measurements are concerned, not saying in practice for the final print), and roughly 0.1 mm accuracy (or better!). This means that the final print might be off 0.05 mm or so in total height, but the details would be single micron (again if the rest of the printer were up to this). For reference bacteria are generally 1.1 to 1.5 microns wide and 2 to 5 microns long. So this is _really_ small!

I don't know of many applications were using the cured resin is okay, but being 0.05 mm off is not.

----------


## Aztecphoenix

> True, and I suppose this is something that a lot of us in this thread have lost sight of.
> 
> Still, it's fun to daydream about taking a $100 printer and making it into a top-tier machine through addons and mods.


We haven't lost sight of it but I think it's safe to assume that the majority of us are makersnd as such we live for the challenge of taking something and putting our own spin on it to make it better.

the only people who are hurt buy this are those who want to make money by forcing us to buy upgrades every year. LONG LIVE OPEN SOURCE!!!!!

----------


## Anuvin

I don't mean to discourage this work, because I think that while it may be overkill, it is still awesome. But a few microns is not a big deal, really.

----------


## jstrack2

> I don't mean to discourage this work, because I think that while it may be overkill, it is still awesome. But a few microns is not a big deal, really.


Haha yeah that's what I meant. The ~1 micron resolution made possible by the drips will exceed what the human eye could ever see without a microscope or something. An accuracy of 0.1 mm or (or better!) is plenty. If more is desired then a couple dollar more caliper or maybe also a scale could do 0.02 mm haha! But yeah 0.02 mm accuracy measurements are definitely not needed (even 0.1 mm is pushing it a bit).

----------


## jstrack2

I purchased this digital caliper for $9.19 (now it is $11.59): http://www.ebay.com/itm/271477770522...84.m1439.l2649

I took it apart, removed an internal metal strip that added friction and put it back together. Now the caliper slides effortlessly, perfect for the float idea. I am real busy this week so I doubt I will get to it in the next few days, but I will relatively soon try to build a float just to prove the idea works. I am not a beta tester, so there will be no printer involved. I will just have water dripping, a container and the caliper with the float attached. After seeing it slide so easily I am convinced that I can make the physical caliper float system work. That just leaves the electronics side, but in my experience that is by far the easy part.

----------


## Aztecphoenix

> I purchased this digital caliper for $9.19 (now it is $11.59): http://www.ebay.com/itm/271477770522...84.m1439.l2649
> 
> I took it apart, removed an internal metal strip that added friction and put it back together. Now the caliper slides effortlessly, perfect for the float idea. I am real busy this week so I doubt I will get to it in the next few days, but I will relatively soon try to build a float just to prove the idea works. I am not a beta tester, so there will be no printer involved. I will just have water dripping, a container and the caliper with the float attached. After seeing it slide so easily I am convinced that I can make the physical caliper float system work. That just leaves the electronics side, but in my experience that is by far the easy part.



just remember to keep track of how much water displacement there is on the float, if it fluxuates it will throw off your measurements.

----------


## rylangrayston

Wow just read this hole thread 

ALOT of great ideas here.... 

ill be bringing them up at a meeting soon 

I loved the tone detection for the start and end of the print, so simple and uses just wire. 

We have been making a fairly inexpensive capacities feed back thing for the peachy pro, ( closed loop galvos ) 
and im really curios to know it the capacitance's of the body's of water in the 2 reservoirs  can inform us of there levels. 
perhaps capacitance between the water and a laminated strip of tin foil on the side wall of the upper reservoirs.



I like the idea of closing the feed back loop with capacitance or pressure sensor chips, but still using drips as the very fine grain measure.
I wonder if we can leverage some leaver action to cause these chips to be 10 times more or 10 times less sensitive that they are naturally, if so that could make for a hack that works for both really big and really small printers, using the same chip. 

@jstrack2  Im really looking forward to seeing some detailed results and pics of the 9 dollar caliper & float system, we have a pair of supper cheap calipers here at the hacker space  :Smile:  if what your suggesting works 
ill probably build one two  :Smile: 

Peachy will alwase aim to make a supper affordable 3d printer but we also want to take a shot at making pro printers too ... so even solutions that cost a bit more can make it into a slightly different printer.
and of course modding the 100 dollar printer is what its all about!! 

Great thinking everyone!!!

----------


## Feign

It occurs to me too that the Peachy already has a "signal out" on the board that goes to the drip sensor...  If the software gets a constant tone on the drip sensor, would that effectively stop the count, or would it keep rising from fluctuations in the tone?

If the former, then the two-wire calibration might be something that the beta testers can try with the Peachys they already have...  Just as long as they can disconnect the "tone out" line when they actually want to print.

----------


## nka

If you stick the two cables, the count upgrade by one only. Until you unstick them and stick them again.

You can try this, even without the Peachy. Just need the software.

----------


## Feign

Well, that's good news!

So yeah, pretty simple way to do an auto z-level calibration:


```
From Drip Sensor Out                                                                     To Microphone in
    |___________________________________________________________                                  |
         |                                                      |"tone line"                      |
         |___Drip count assembly___                             |                                 |
                                   |  -(top of the tank)-       |                                 |
                                   |                            |                                 |
                                   |       (1mm vertical spacing between tone line and gap)       |
                                   |_____________________ [Gap] __________________________________|
```


Not actually code of course, I just needed a way to keep the spaces in the formatting, to make this little wiring diagram make sense.  Place it in the tank, make sure it's level, start dripping saline, after the level is above the sensor, look at the drip count and subtract 1 to get the number of drips per millimeter.  Dry off the "sensor" and repeat in a different part of the tank as desired to get a good average.

If there were a piece of acrylic with exactly a millimeter spacing between three wire-sized gaps, that would make it even easier.   :Big Grin:

----------


## jstrack2

Thanks Rylan! Yeah I am excited to make it. Having such good accuracy and resolution will be great. I really like  Mike Biddell and Nahoj's caliper and scale ideas.

What do you think about shining the laser up to hit the resin below the top of the liquid (the topic I started about using three layers). I think it is a pretty simple way to fully remove the ripples. I'm not sure how much of an issue they are, but it seems they must hurt the potential print quality some.

----------


## jstrack2

Good point Aztecphoenix. I was thinking about the same thing. The float will have to avoid having significant friction against the wall. This effect will likely be small, but more than the 0.02 mm resolution the caliper is capable of! (Which amazes me that is possible for nine dollars)

----------


## rylangrayston

> Thanks Rylan! Yeah I am excited to make it. Having such good accuracy and resolution will be great. I really like  Mike Biddell and Nahoj's caliper and scale ideas.
> 
> What do you think about shining the laser up to hit the resin below the top of the liquid (the topic I started about using three layers). I think it is a pretty simple way to fully remove the ripples. I'm not sure how much of an issue they are, but it seems they must hurt the potential print quality some.


Ill go have a look at it now... 
mostly it hurts the speed at which we can print good looking things because we have to wait for the resin to flow over top.

----------


## rylangrayston

> Well, that's good news!
> 
> So yeah, pretty simple way to do an auto z-level calibration:
> 
> 
> ```
> From Drip Sensor Out                                                                     To Microphone in
>     |___________________________________________________________                                  |
>          |                                                      |"tone line"                      |
> ...


multiple "tone Lines"  at different heights ?
the code is avalible here:
https://github.com/PeachyPrinter/peachyprintertools
feel free to pull request once you have added this handy feature  :Big Grin: 

In fact i could use this now! it would alow me to go to bed an hour earlier! as im currently waiting for a drip test to finish lol

----------


## Feign

Ah, sadly, I'm no coder.  Though what I was getting at is that this mod might not even need a coding change, it's just a change in the physical wiring of the drip sensor.

----------


## rylangrayston

hmm 
i can see a way for that to work too. 
simply take both wires from the dripper and
wire them to a desired height of the container ... when the water touches the to wires it will short out the dripper 
and drips will no longer be counted. 

You could also simply put the correct amount of water in the top container and let it all run threw 



```

|
|-------------------------------------------
D                                          |
R                                          |
I                                          |
P                                          |
P                                          |
E                                          |
R                                          |
|------------------------------------      |
|                                    |     |           |
                                 H   |     |  H
                                 H            H
                                 H            H
                                 H            H
                                 H____________H
```

----------


## User_Defined

Hey Guys, I've been following this forum for a few weeks now and have a few things to add:

Firstly I think it is a great idea to have a secondary validation of Z height. I've heard the Kalman filter come up a lot in positional robotics, and it sounds very interesting.

As for sensing the Z height, I think that the suggestion of using a strip of foil on the side of the top reservoir is absolutely brilliant. I would likely use copper foil as it is easy to solder wires to, and comes in standardized thin tape rolls.

This would only work with relatively thin dielectric walled containers, and would likely need a calibration step. You would also need to have another wire inside the reservoir to complete the circuit. Once calibrated, the capacitance should be linear with salt water height.

I don't know what the Peachy uses for electronics, but the way I would implement this is to use a 555 timer as a capacitance meter, and then send the square wave signal to the computer.  Audio works best since you can just pulse modulate your drip received signal so every droplet interrupts the current state of the Z height. Imagine two people, one constantly expressing their detailed undying love towards the current height of the reservoir, and another impulsive and insensitive colleague occasionally interrupting them to announce when a droplet has been received.

Schematic: http://www.eleccircuit.com/simple-ca...-using-ic-555/
(One of many out there)

I would go for the newer 2MHz capable 555's since the capacitance may be in the pF range.



Regarding drips and droplets:

I worked for four years in a chem lab before engineering, and we used Pasteur Pipettes to dispense droplets for assays. They are thin glass tapered tubes that produce consistent droplets (apparently (I hope since I used them a lot!)) and would have a tiny bulb at the end. They would be sold very cheap sans-bulb and could be a better option than what is currently being used. (By simply connecting them to the rubber tubing)

The other detail about the drip I am fuzzy on is that long thin tube which transmits the droplets to the reservoir below... wouldn't it be more consistent to have a big tube with the droplets falling straight down into the salt water?


That's all I got!

I really really really hope this peachy printer thing works out... good luck guys and gals!


-UD

----------


## Synchron

Hi,
i had the idea of messuring the height outside the water. thies would be possible when the water level would be raised by communicating vessels. I tried to draw a little pic of what i mean, hope you understand it  :Big Grin: 

peachy_communicatingVessels.jpg

The Z height could so be messured by the distance of the right vessel to the ground. Or by a potentiometer at the turning point of the mechanism. As second plus the distance from the printer to the waterlevel would be constant.
Synchron

----------


## Synchron

Oh, i've forgotten to explain, how i thought it could do the "drops".
I thought of something like a "clock escapement" with a big wheight under the right tank. it could be run continuusly (like a clock) or be triggert by the laser.
to make the next print, you can raise the left tank by hand, and separate the water from the resin with a simple valve at the tube.

----------


## rylangrayston

> As for sensing the Z height, I think that the suggestion of using a strip of foil on the side of the top reservoir is absolutely brilliant. I would likely use copper foil as it is easy to solder wires to, and comes in standardized thin tape rolls.
> 
> This would only work with relatively thin dielectric walled containers, and would likely need a calibration step. You would also need to have another wire inside the reservoir to complete the circuit. Once calibrated, the capacitance should be linear with salt water height.
> 
> I don't know what the Peachy uses for electronics, but the way I would implement this is to use a 555 timer as a capacitance meter, and then send the square wave signal to the computer.  Audio works best since you can just pulse modulate your drip received signal so every droplet interrupts the current state of the Z height. Imagine two people, one constantly expressing their detailed undying love towards the current height of the reservoir, and another impulsive and insensitive colleague occasionally interrupting them to announce when a droplet has been received.
> 
> Schematic: http://www.eleccircuit.com/simple-ca...-using-ic-555/
> (One of many out there)
> 
> ...


Im really liking the foil in water idea to ... im going to give it a home.... there done:
http://3dprintboard.com/showthread.p...6836#post16836

Good idea by the way soldering aluminum :S

"Pasteur Pipettes".. thanks for that also goggling now. 
Ahh yes your right, ive used those before in the dripper of the peachy printer ... they did make better drips because they have thin tips and the water really beads on that plasitc/ glass. 

Thanks User_Defined

----------


## jstrack2

Here is a video of me pouring a cup full of water and the caliper measuring the water level rise. 



Sorry the video is kind of bad, it is hard to pour and record. I can do another if someone wants. Anyway here is a picture of the setup. caliper1.jpg

It is pretty sloppy, but I just wanted to demonstrate here that a caliper can be used. The float doesn't need to be anywhere near this large btw haha. Also to save weight and get more consistent sliding this part pictured can be removed and replaced with a small piece of plastic.
caliperpartremoved.jpg 

If the peachy printer had nicely cut plastic parts I think this would be very simple and consistent. One thing to pay attention to though is that the float should be counterbalanced since the caliper adds some torque. To do this a plastic "tail" could be added to the float.

Also I attached the caliper to the computer via an Arduino.

arduinocaliper.jpgcaliperdata.jpg

I didn't really have to do any work here, a tutorial is online: https://sites.google.com/site/martha...igital-caliper

There are microcontrollers that are a dollar or two that would work here too, I just used an Arduino since I had it laying around. Let me know if anyone has any questions or concerns!

----------


## jstrack2

Here is a much improved video:




As you can see it is pretty stable despite being a very rough setup:
floatwithbalance.jpg

I used the empty cup here to counterbalance the torque from the caliper and caliper to float attachment. If well designed, laser cut plastic was used then the float could be far smaller and even much more stable.

----------


## jstrack2

Also if ordered in high volume it seems like the caliper could be really cheap. The battery, lcd screen and some metal parts would not be necessary. It is already only nine dollars for a single unit (including shipping!) with that stuff. Also if more than 15 cm is desired in the z direction then it may be possible to attach multiple of the ruler part of the caliper together. Or maybe longer ones could be manufactured in the first place. This might be an easier, more consistent way than the method of having a capacitor made out of foil. I am real interested to see how well that works too though! I can't wait to see prints that use the drip and some accurate z measurement in conjunction with a Kalman filter. Such extreme control of the z axis is really interesting!

----------


## Aztecphoenix

Check out what I found on Kickstarter that may be the answer to our prayers

https://www.kickstarter.com/projects...?ref=discovery

----------


## Feign

While it's cool that this is everything we're looking for together in a package...  It's also $79 for something that might take at most $30 to make as a DIY project.

----------


## Aztecphoenix

> While it's cool that this is everything we're looking for together in a package...  It's also $79 for something that might take at most $30 to make as a DIY project.


Well I'm just waiting for someone to do it as a DIY I'm too much of a noob to figure it out

----------


## mike_biddell

In theory, if you have three channels in a plastic tube (a centre channel sandwiched between 2 outer channels) and you put two narrow flat plates in the outer channels. Then you let water rise up the centre channel as the water in the tank rises. You have a very sensitive variable capacitor in which the capacitance varies with the fluid level. A capacitance bridge could measure the variation very accurately. This method would work for any depth of tank. The water acts as a dielectric between the plates. Oh, the outer tubes are sealed.

----------


## jstrack2

Aztecphoenix, what I did is a DIY way! haha If you want I can help you build it. I think that if the Peachy team makes laser cut parts then that will be best. It will cost almost nothing and work perfectly, with virtually 0 set up time. What I did was super sloppy (I used random metal, plastic and styrofoam glue gunned together and a random cup as a counterbalance), yet surprisingly still worked well!

Again though the Kalman filter will need to be implemented too. This will lead to the extreme z-axis control. Like Mike Biddell I was amazed at how well it works when I first implemented it for something else. And the beauty is that it is just software. Once written it is free!

----------


## jstrack2

Mike Biddell, I agree that your idea would work in theory (water has a huge dielectric constant!), but in practice I don't know if it is worth doing. Very accurate measurement methods that take very little work can be purchased for just a few dollars. This method strikes me as something that will take a lot of work to get right. Besides getting it manufactured which is non-trivial, I think that there are other things to watch out for. A temperature sensor would be needed since the the dielectric constant of water varies pretty strongly with temperature. Also it varies a little with different levels of salinity.

That said I might be wrong! If you could make it work that would be great since it is pretty hard to beat the simplicity of dropping a tube into the water!

----------


## mike_biddell

Jstrack..... agreed..... there could be a lot of graft involved........ the cheap calipers are the best option.

----------


## jstrack2

Yeah there could be a lot of money exchanging hands working on something like that! Haha jk

----------


## rylangrayston

Some how ive been missing all the convo in this thread until now.... Yet Ive been working on much of the same stuff. 

1. jstrack2.. wow great job!! That last video really shows that the caliper method can work! amazing how smooth it is! and the read out already hacked into the arduino! 

2.  We got capacitive feed back working quite well here at peachy a few weeks ago, its showing real promise. 
I had never heard of the Aqua Plumb before, it definitely looks like capacitive feed back too but I dont know how they did it with such small wires! 
We have to use large plates to get the resolution we need. Sorry Im too pressed for time to post about it right now but the time will come.

3. Thanks for posting about the Kalman filter, ive sent an email about that to James Townly so he knows about it.

----------


## Aztecphoenix

Ok, for all the techies out there, to compensate for the salinity variables and having to calibrate prior to each print, what about having a sensor in the salt water tank which would automatically read the saline level to calibrate the capacitive sensor in the build tank?

----------


## rylangrayston

> Ok, for all the techies out there, to compensate for the salinity variables and having to calibrate prior to each print, what about having a sensor in the salt water tank which would automatically read the saline level to calibrate the capacitive sensor in the build tank?


hmm .... google ing .... yep! 
http://web.cecs.pdx.edu/~eas199/B/ho...or_wiring.html

----------


## BrockMcKean

If the saline solution is mixed well enough, yes. If it's not because you didn't physically disturb it enough or you used cooler water, the salinity in one area is going to be different than another area. You would have to assume the person followed instructions to ensure it was properly mixed to a homogeneous state. In my opinion it would be simpler just to come up with an way of using an absolute amount of water and absolute amount of salt at an absolute temperature. That is to say, ensure the error in mixing is very small due to the simplicity and rigidity of the mixing process. I'm sure there's something like this out there, but I'm a computer engineer, not a chemist.  :Smile:

----------


## 3dspider

has anyone tried using an AD7745 Capacitance to digital converter with a flat speaker wire in place of the capacitor? If the ends of the wire were waterproofed, an AD7745 should be able to detect the minute changes in capacitance in the wire as the water level was raised/lowered. Datasheet available here

----------


## Jukurpa

Sorry if it has already be proposed before, but for a Z-axis calibration, couldn't we just print a predetermined shape, for example, a tube (which is the easiest with two sinus signals) for a know quantity of drops and then, measure the final print with a caliper (yes, maybe not everybody have a caliper, but at least, the poeple in the beta team).
So, for X drops, we've a tube of Y mm and then, we know the thickness of the layer added by a drop. These could be parameters for the slicer, or even be included in the Peachy Printer software.

And not knowing the Z-axis speed, I suppose there is no problem to print the tube at "full speed" for the X and Y axis, several passes on the same layer shouldn't cause any problem... I suppose.

----------


## Chayat

I think that's the very basic method, you'll be assuming a perfectly walled build tank and perfect drip uniformity. I think the things that are being discussed assume that calibration has already been done.

----------


## Jukurpa

Yes, I understand it's the very basic method, but the one with the less impact on the final cost of the printer.
And even if the tank is perfectly build, the use of two sinus signals leads more to a "cone" than a tube in fact.
That aws only my two cents, even if it must be obvious for most of the beta testers  :Stick Out Tongue:

----------


## Aztecphoenix

I have been experimenting with a home built variable capacitor the past few days and have made a discovery, my initial worries about the varience of salt in the water has turned out to be the least of our worries for a reliable means of determining Z height, the difference in water temperature as well as disolved solids in the water have a huge effect on the capacitors feed back I have however begun work on a work arround, an additional sensor array that is to be used to factor in all the veriables and constantly automatically calibrate the capacitor.

I am trying to design this whole system on a budget as well as trying to design the parts in such a way that it is possible to laser cut many of the pieces however, the final system is going to require a microprocessor and possibly some software for calibration, therein lays the problem, building the prototype isn't that much of a problem yet (I still have a little bit of research to do) but my programming skills are nearly non-existant, so I am comming to the forum to see if there is anyone interested in assisting on the software side of things, so far it looks like the build my be around $50 to build (but like I said, there is still a little more work to be done) I may also require some help with the electronics side for the final circuit.

anyone willing to lend a hand please let me know and we will see what we can do

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## rylangrayston

> I have been experimenting with a home built  variable capacitor the past few days and have made a discovery, my  initial worries about the varience of salt in the water has turned out  to be the least of our worries for a reliable means of determining Z  height, the difference in water temperature as well as disolved solids  in the water have a huge effect on the capacitors feed back I have  however begun work on a work arround, an additional sensor array that is  to be used to factor in all the veriables and constantly automatically  calibrate the capacitor.
> 
> I am trying to design this whole system on a budget as well as trying to  design the parts in such a way that it is possible to laser cut many of  the pieces however, the final system is going to require a  microprocessor and possibly some software for calibration, therein lays  the problem, building the prototype isn't that much of a problem yet (I  still have a little bit of research to do) but my programming skills are  nearly non-existant, so I am comming to the forum to see if there is  anyone interested in assisting on the software side of things, so far it  looks like the build my be around $50 to build (but like I said, there  is still a little more work to be done) I may also require some help  with the electronics side for the final circuit.
> 
> anyone willing to lend a hand please let me know and we will see what we can do



Hey Aztecphoenix 
It may be a little while before we get to  it, but we will likely write software right in to the peachy driver/  printing interface that is meant to detect capacitive feed back. 
The  testing we have done here at peachy confirms most of what you said  about capacitive feed back.  We havent Graphed temperatures affect and  im really curious to know more about that. 
Since your actualy doing  this, it might be good to start a new thread to document your work in.  If you can be very descriptive (vids and pics of what you have set up )  Ill be more able to get involved. 
There is also this Thread on the topic of Capacitive feed back, and there you can see that colehard has made some progress on this as well. 
http://3dprintboard.com/showthread.p...gt-freq-gt-mic

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