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

[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.

[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.

[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.

[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.

[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/

[nka]

or what about Ultrasonic Proximity Sensors?

Is the precision good for that?

[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.

[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)

[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.