DIY ILDA Projector - Technical Difficulties

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11-12-2020, 01:47
tboultwood

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DIY ILDA Projector - Technical Difficulties
Morning,

I have posted a couple of times with great news! Since starting this project I do have a working laser projector whic has been by far the 'coolest' project, however I am now looking to solve possibly the finally hurdle.

Currently I am using an audio card which works flawlessly and I am really happy about it's results. For those of you who don't know using an audio card is perfect for the job and sending 6 channel audio with a correction amplifier for the galvos works fine.

Up until this point - the software I have created allows me to generate audio from ILDA files, my issue is the following.

The laser module accepts a TTL signal, either high or low. Currently I have written in the software to output High or Low(audio max or audio min) to turn the laser on/off at the correct time which works...

There are two main reasons why I want to incorporate a better solution.
- It's too bright - feedback from friends and family is that after watching the show their eyes begin to hurt, really bad for safety and currently no ability to turn the brightness down.
- I can only display 8 colours max. - I want each R G B laser to be 8 bit such to see the ILDA projections how they were supposed to be seen.
What have I done to try and rectify the problem? What am I asking for?

I started by trying to modify the open source Helios DAC show card. I had some good progress with this, This would solve all the problems and even update my projector to be fully USB. I could then use other pieces of software and not my home made software. I won't go in too much detail but I essentially wanted to output a PWM signal from this instead of an SPI which chucks the values down a DAC. Could I not just buy one? Yes - but I would actually be in the same situation. Does it work? Sadly no, not much user support on writing code at home on a specific SAM4 arm cpu...

I have today put an arduino in between the laser module and audio sound card. I could easy read the analog voltage and set a PWM to a mapped value form the signal. In my head this works great. However the arduino I am using is not up to the challenge. I think the program is running two slowly. I need to analog read 3 signals, do some quick math, and generate a PWM at a frequency of at least 40khz - (Nyquist theory, but probably more like 4x).

A couple of pictures of this attempt can be found attached.

I thought about a VCO - voltage controlled oscillator? But all the chips don't have the frequency I am after...... Those who have built one, what did you do?
Does anyone have a analog controlled laser module to their knowledge?

Thank you, I am happy to discuss with anyone who wants to build one....
TLDR - Analog voltage to control a TTL laser module.
11-12-2020, 05:07
james

Why don't you just get analog modulated laser diode drivers?
11-12-2020, 06:33
laserist

Or go really old school and put a blacken metal shutter part way into the beam. Called an intensity control device when attached to a gm20 galvo in Laserium speak.
11-12-2020, 12:55
mixedgas

Quote:

Originally Posted by laserist

Or go really old school and put a blacken metal shutter part way into the beam. Called an intensity control device when attached to a gm20 galvo in Laserium speak.

Ever hear of the TL494 or SG3524 PWM chips? Take your analog input and drive one. Use that instead of modifying the Helios. Not my preferred way of making PWM for controlling lasers, I prefer to use a digital comparator and a flash A/D converter with a counter, but it would get you pseudo-dimming with your TTL laser. Better then re-inventing the wheel, as you will soon prefer analog drivers. PWM really sucks for display lasers, because you really want to run at sampling times of 4-6 times the PPS rate. That gets you into really fast current sources which are just as difficult to stabilize as analog designs.

Now if you have an external AOM or EOM modulator on your laser, PWM can do awesome things. But that is not the case here.

Steve
11-12-2020, 12:57
mixedgas

Quote:

Originally Posted by laserist

Or go really old school and put a blacken metal shutter part way into the beam. Called an intensity control device when attached to a gm20 galvo in Laserium speak.

Ever hear of the TL494 or SG3524 PWM chips? Take your analog input and drive one. Use that instead of modifying the Helios. Not my preferred way of making PWM for controlling lasers, I prefer to use a digital comparator and a flash A/D converter with a counter, but it would get you pseudo-dimming with your TTL laser. Better then re-inventing the wheel, as you will soon prefer analog drivers. PWM really sucks for display lasers, because you really want to run at sampling times of 4-6 times the PPS rate. That gets you into really fast current source drivers s which are just as difficult to stabilize as analog designs. In other words PWM usually has to be faster then what the diode driver can respond to.

Now if you have an external AOM or EOM modulator on your laser, PWM can do awesome things. But that is not the case here.

Steve

Edited because I had one part number wrong, Tl494, and there is also TL594,, a rarely used successor chip.

Steve
11-13-2020, 05:10
tboultwood

1 Attachment(s)
Quote:

Originally Posted by mixedgas

Ever hear of the TL4594 or SG3524 PWM chips? Take your analog input and drive one. Use that instead of modifying the Helios. Not my preferred way of making PWM for controlling lasers, I prefer to use a digital comparator and a flash A/D converter with a counter, but it would get you pseudo-dimming with your TTL laser. Better then re-inventing the wheel, as you will soon prefer analog drivers. PWM really sucks for display lasers, because you really want to run at sampling times of 4-6 times the PPS rate. That gets you into really fast current source drivers s which are just as difficult to stabilize as analog designs. In other words PWM usually has to be faster then what the diode driver can respond to.

Now if you have an external AOM or EOM modulator on your laser, PWM can do awesome things. But that is not the case here.

Steve
Quote:
Originally Posted by tboultwood

Morning,

I have posted a couple of times with great news! Since starting this project I do have a working laser projector whic has been by far the 'coolest' project, however I am now looking to solve possibly the finally hurdle.

Currently I am using an audio card which works flawlessly and I am really happy about it's results. For those of you who don't know using an audio card is perfect for the job and sending 6 channel audio with a correction amplifier for the galvos works fine.

Up until this point - the software I have created allows me to generate audio from ILDA files, my issue is the following.

The laser module accepts a TTL signal, either high or low. Currently I have written in the software to output High or Low(audio max or audio min) to turn the laser on/off at the correct time which works...

There are two main reasons why I want to incorporate a better solution.

It's too bright - feedback from friends and family is that after watching the show their eyes begin to hurt, really bad for safety and currently no ability to turn the brightness down.
I can only display 8 colours max. - I want each R G B laser to be 8 bit such to see the ILDA projections how they were supposed to be seen.

What have I done to try and rectify the problem? What am I asking for?

I started by trying to modify the open source Helios DAC show card. I had some good progress with this, This would solve all the problems and even update my projector to be fully USB. I could then use other pieces of software and not my home made software. I won't go in too much detail but I essentially wanted to output a PWM signal from this instead of an SPI which chucks the values down a DAC. Could I not just buy one? Yes - but I would actually be in the same situation. Does it work? Sadly no, not much user support on writing code at home on a specific SAM4 arm cpu...

I have today put an arduino in between the laser module and audio sound card. I could easy read the analog voltage and set a PWM to a mapped value form the signal. In my head this works great. However the arduino I am using is not up to the challenge. I think the program is running two slowly. I need to analog read 3 signals, do some quick math, and generate a PWM at a frequency of at least 40khz - (Nyquist theory, but probably more like 4x).

A couple of pictures of this attempt can be found attached.

I thought about a VCO - voltage controlled oscillator? But all the chips don't have the frequency I am after...... Those who have built one, what did you do?
Does anyone have a analog controlled laser module to their knowledge?

Thank you, I am happy to discuss with anyone who wants to build one....
TLDR - Analog voltage to control a TTL laser module.
Quote:

Originally Posted by laserist

Or go really old school and put a blacken metal shutter part way into the beam. Called an intensity control device when attached to a gm20 galvo in Laserium speak.

Thank you all for your insights especially with the TL4594 information, that was what I was looking for.

I did some more tinkering this morning and thought I would see how results differed between that of an arduino nano and a ESP32. Whilst I knew the ESP32 run almost a magnitude faster it turns out the PWM can be configured in such a way to offer me the frequency I am after.

As Steve quite rightly mentioned 4 or 5 times faster than the scanning rate (mine being 20kpps) I set the esp32 PWM to 100k and after discovering one line was connected to the reset line of the ESP32 I have got something now that ticks the boxes. (find image attached). The final step is to develop my 3rd round of PCBs.

This was my last hurdle and I have spent all afternoon fixing all the bugs with my software and now works almost flawlessly, the only downside is with larger ILDA files it takes a little annoyingly longer to compute files.

I'm not sure how ill fill my time that this is now nearly completion, i guess lock down however will soon end again.

Thank you!