turn laser off

How are we turning the laser OFF ? Is it zero X and Zero Y? Or maximum X and maximum Y? With the former into a NAND gate, that should work .....but I suppose with a design that comes to a point, you might need zero x and zero y? It's at times like this, a bit of local intelligence in the Peachy box would be useful.

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Originally Posted by mike_biddell

How are we turning the laser OFF ? Is it zero X and Zero Y? Or maximum X and maximum Y? With the former into a NAND gate, that should work .....but I suppose with a design that comes to a point, you might need zero x and zero y? It's at times like this, a bit of local intelligence in the Peachy box would be useful.

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I think local intelligence is the answer. Include a picaxe chip on the peachy pcb. This could then recognise a bit bang code from the audio port to switch the laser on and off. The picaxe could also have a push button input, which when pressed, generates a square wave for creating Y displacement for scanner mode. The incremental cost would be about $4, but well worth it.

Excuse my ramblings.... the same picaxe could drive the stepper motor in the scanning turntable. I'd say a picaxe on the PCB is almost essential for very small incremental cost.

I'm not sure to what extent you can bitbang through an audio port - it's really not designed for that and there may be filtering provided by the audio chip that cannot be disabled.

As far as I know there are still no plans for a microcontroller on the Peachy. The aim appears to be to stick with simple analogue circuits (like the amplifier) where possible. I'd imagine that the laser could be turned off just by thresholding a derivative of the voltage inputs. This would tell you whether the laser is moving. If the laser is not moving, you turn it off. I can't think of any situation where you'd want the laser turned on but stationary.

I suspect that someone will do a microcontroller board for the Peachy at some point, or repurpose one of the ultra-cheap STM32 Discovery boards for that purpose. $10.90 (from Digikey) is hard to beat for a board that includes a bunch of RAM/ROM (48KB/256KB), hardware floating point and DSP functionality, 12-bit ADCs and DACs for moving the mirrors around and sending water droplets, and built-in op-amps for more analogue stuff. It's even got a full 9-DOF IMU on there, although I can't really think of anything to use this with on the Peachy.

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Originally Posted by Slatye

I'm not sure to what extent you can bitbang through an audio port - it's really not designed for that and there may be filtering provided by the audio chip that cannot be disabled.

As far as I know there are still no plans for a microcontroller on the Peachy. The aim appears to be to stick with simple analogue circuits (like the amplifier) where possible. I'd imagine that the laser could be turned off just by thresholding a derivative of the voltage inputs. This would tell you whether the laser is moving. If the laser is not moving, you turn it off. I can't think of any situation where you'd want the laser turned on but stationary.

I suspect that someone will do a microcontroller board for the Peachy at some point, or repurpose one of the ultra-cheap STM32 Discovery boards for that purpose. $10.90 (from Digikey) is hard to beat for a board that includes a bunch of RAM/ROM (48KB/256KB), hardware floating point and DSP functionality, 12-bit ADCs and DACs for moving the mirrors around and sending water droplets, and built-in op-amps for more analogue stuff. It's even got a full 9-DOF IMU on there, although I can't really think of anything to use this with on the Peachy.

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errrrr you can bit bang through an audio port ...... errrr the only time you would want to turn the laser off is if it is moving ???? to move to a new print site..... e.g. if you are printing a two legged figure and you are on the legs of a vertically orientated figure, so that the resin is not hardened in the transit path. There's no point in turning the laser off if its static in the print area.

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Originally Posted by mike_biddell

errrrr you can bit bang through an audio port ...... errrr the only time you would want to turn the laser off is if it is moving ???? to move to a new print site..... e.g. if you are printing a two legged figure and you are on the legs of a vertically orientated figure, so that the resin is not hardened in the transit path. There's no point in turning the laser off if its static in the print area.

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I know I'm rambling LOL, but I'm not sure why you would spend $10 when you can spend $2-3.
Picaxe chips have ADC, and PWM/DAC, plus E squared and ROM and RAM.
If you bit bang the audio signal, it remains true to the original concept of audio input only.
Four bits should be sufficient e.g. 1010 = laser ON and 0101 = laser OFF. logic 1 would be full mirror deflection and logic zero would be no mirror deflection.
These bits must be transmitted at a rate much greater than the mirror slew rate so that it doesn't have time to move before the laser is switched ON or OFF.
The audio would be zenered to 5V and input to the ADC input of the picaxe.

Without laser ON and OFF, some prints may prove impossible. For instance a 6 inch figure with two legs astride as I mentioned before. You could turn this figure horizontal, but you would have large x or y deflections from the normal and this could cause beam focus/spread problems.

Any evidence of bitbanging through an audio port? Not that I disbelieve you, just that I can't remember seeing it done. It seems like you might have to do some rather interesting coding to make the sound chip output what you want at the right time, and the coding might have to differ between sound chips.

Fair point about the laser, hadn't considered that aspect. I gather that they've already sorted out a way to turn it off, and exactly how it's done will be interesting to see. I suppose the alternative to what I posted above is to threshold the other way - so that if the beam is moving really fast (too fast to properly cure the resin) you turn it off, but if it's moving at normal printing speed then you turn it on. Presumably the transitions between two non-printing sections would be done at maximum speed while the printing itself might be a bit slower.


The $10 on the STM32 board is for a complete board. The PICAXE equivalent is $40 at Digikey. I was suggesting that because it appears that the project founders won't be using a microcontroller on their board, so anyone who wants one on the Peachy will have to get their own board. Apart from Arduino Nanos from eBay, I don't think there's anything cheaper than the STM boards. Certainly nothing with that level of performance.

If you were including just the bare chip, then a cheap ARM one will cost about $1.50 (and will still absolutely destroy any 8-bit microcontroller), or $6 if you want the floating point and DSP stuff. This is often attractive because, while it makes the board a bit more expensive, it makes the code a lot cheaper. No need to spend time optimising routines in fixed-point arithmetic when the chip will handle floating point just as fast. The USB support is also nice because it allows for firmware updates (good luck doing that over an audio port) and easy expansion later on.

Edit: in any case, it's not really an issue. The Peachy founders have found a way to turn the laser on/off over the audio link, and that's really all that matters for us. As long as it works, no need for a microcontroller on there.

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Originally Posted by Slatye

Any evidence of bitbanging through an audio port? Not that I disbelieve you, just that I can't remember seeing it done. It seems like you might have to do some rather interesting coding to make the sound chip output what you want at the right time, and the coding might have to differ between sound chips.

Fair point about the laser, hadn't considered that aspect. I gather that they've already sorted out a way to turn it off, and exactly how it's done will be interesting to see. I suppose the alternative to what I posted above is to threshold the other way - so that if the beam is moving really fast (too fast to properly cure the resin) you turn it off, but if it's moving at normal printing speed then you turn it on. Presumably the transitions between two non-printing sections would be done at maximum speed while the printing itself might be a bit slower.


The $10 on the STM32 board is for a complete board. The PICAXE equivalent is $40 at Digikey. I was suggesting that because it appears that the project founders won't be using a microcontroller on their board, so anyone who wants one on the Peachy will have to get their own board. Apart from Arduino Nanos from eBay, I don't think there's anything cheaper than the STM boards. Certainly nothing with that level of performance.

If you were including just the bare chip, then a cheap ARM one will cost about $1.50 (and will still absolutely destroy any 8-bit microcontroller), or $6 if you want the floating point and DSP stuff. This is often attractive because, while it makes the board a bit more expensive, it makes the code a lot cheaper. No need to spend time optimising routines in fixed-point arithmetic when the chip will handle floating point just as fast. The USB support is also nice because it allows for firmware updates (good luck doing that over an audio port) and easy expansion later on.

Edit: in any case, it's not really an issue. The Peachy founders have found a way to turn the laser on/off over the audio link, and that's really all that matters for us. As long as it works, no need for a microcontroller on there.

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The only way I can think of turning the laser ON and OFF with analogue, is a bandpass filter. That is, you send a tone burst at a very specific frequency. That would work, but it doesn't have the spin off benefits of scanner Y square wave drive and scanner stepper motor drive, for a bare $3 extra.

Its already done. See update 19
https://www.kickstarter.com/projects...r-and-sc/posts
under Here’s a list of our major accomplishments over the past couple weeks:
Got the circuit to turn the laser on and off

it detects a high frequency wave and turns off the laser (at least thats what they said in some earlier update).

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Originally Posted by masterada

Its already done. See update 19
https://www.kickstarter.com/projects...r-and-sc/posts
under Here’s a list of our major accomplishments over the past couple weeks:
Got the circuit to turn the laser on and off

it detects a high frequency wave and turns off the laser (at least thats what they said in some earlier update).

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That's exactly the method I describe above (band pass filter and tone burst, with high enough frequency not to move the mirror). Still think that's a lost opportunity !!!!! Thinking about integration with a scanning turntable.

The thing is, the audio interface is used because it's an easy way of getting what the Peachy needs (ie analogue signals) without any extra hardware. For that purpose it's ideal. For digital IO it's not great; we already have much better interfaces for that purpose (namely USB and RS232). Other limitations of the analogue output are already well known: it's not consistent (different soundcards behave differently), you need a separate power supply, some devices lack a suitable microphone input, and you can't use the audio hardware for anything else while printing is in progress. Still, it's the easiest way of getting analogue signals from a PC.

For a very small amount of digital IO (eg 1 bit to turn the laser on or off) plus a large amount of analogue IO it still makes sense to keep using the analogue interface and add whatever hardware is needed to extract that single bit from the analogue channel. As soon as you start putting more complex digital IO on there (motor control for multiple motors, feedback from motors, servo control for autofocus, camera input for the scanner, etc) the analogue interface doesn't make any sense. Now you do need a microcontroller (avoiding this seems to be one of the main reasons for sticking with analogue data from the PC), the microcontroller needs a bunch of code written to interpret the analogue data, and the PC needs code written to output the analogue data. The alternative is to just grab a USB device library, turn on the microcontroller's DACs (or use an even higher-quality external DAC) and write a couple of lines of code on the PC to talk to a USB UART. Then you have consistent analogue output (so no need for an amplifier that can handle all sorts of odd soundcard outputs) and more-or-less unlimited IO bandwidth.

Although we have no plans thus far to put a micro controller in the basic peachy printer, we will definitely be using a micro controller in the peachy pro, and you will be able to order the pro board as an add on to your basic peachy printer IF all goes as planed.

Of course there is so much more you can do with a micro, when we add a micro, it will likely be a fairly powerful one and we will explore some of the many possible features in the pro version of the peachy printer.

Currently we are sending the peachy printer an amplitude modulated signal, so the circuit docent care what carrier frequency we use so we change the carrier frequency to switch on the laser and we use high pass filter for this. The nice part about doing it this way is that we continually send the mirrors a position whether the laser is on or off, which means when the laser comes on its already pointing in the correct spot!

@mike_biddell
Great idea to use a micro to drive a rotating scanner platform, that's the kind of thing we will be doing with the pro, of course, this is a freedom respecting project so if you don't want to pay $1000 for our pro you can easily just make your own setup at what ever cost savings you can muster. The peachy is built to be hacked, we will do everything in our power to enable people to add great features to the peachy like the ones you suggest!

OT but @ Ryan: Awesome! Will be ordering upgrade kits, too!!