DIY laser projector project

[Mattronium]

So I've though about building a laser projector for some time now, but I never got around to it. Plus it was slightly daunting to me with the various choices of DAC, Software and hardware.
Well, for my college course I need to build a project, so I decided to get a two for one and get a laser projector and fulfill my project requirements.

So this project is still mostly in the theoretical phase. so of course any suggestions will be helpful. Since I'll be DIY making everything except the scanners my plans are bound for a few revisions along the way to the finished project. So my current plans will not necessarily stay consistent.


Hardware:
I'll have all the optics on the projector mounted on a 7"x15"x1/2" aluminum plate. I'm going to try to put it in an aluminum carrying case. Mirror mounts and dicro mounts use 2" by 1.5" Al angle. This puts the beam height at about an inch.
Diodes are Mits 500, PLT5 450B, and PL 520.

Aluminum plate before cutting.


Optics:
I'll be using the FS mirrors, dicros and lenses from DTR. The 638nm mit's will be corrected using salvaged single axis positive lenses and DTR's lenses.


Electronics:
My current plan is to use (THIS) design for my diode drivers. The 5V is for the input, 9V is power and 8V is simply a consistent voltage for reference. Circuit design is not something I am very good at so I'm figuring it out as I go.

For the DAC I plan to use an arduino possibly with a few external components.


Software: Whatever free software I can find to play with.
So, HE laserscan and LFI.


The projector will be powered by a 16V 4A laptop charger for wall power or 8*18650 Li-ions in series. For the scanners I plan to get some cheap Chinese ones from ebay. While not the best quality. they will work fine for what I want it for. So far my build costs looks like it will be between $300 and $400, so I'm hoping to keep it under $400.

 

[lasersbee]

Re: My DIY laser projector project

You may find a lot of useful and helpful information
on Laser Projectors at PL... (Photonlexicon)

Jerry

 

[paul1598419]

Re: My DIY laser projector project

I wish you luck, Matt. I'm hoping to learn from your mistakes before I tackle this kind of projector for myself. +rep.

 

[ElectricPlasma]

Re: My DIY laser projector project

Very nice! Subbing to see more

 

[Cyparagon]

Re: My DIY laser projector project

Diodes are Mits 500, PLT5 450B, and PL 520.

You'd want to match power and divergence better than that. Also, a 462nm looks much better than 445 in a projector.

For the DAC I plan to use an arduino possibly with a few external components.

Software: Whatever free software I can find to play with.
So, HE laserscan and LFI.

How are you going to get this software to interface with a microcontroller?
Arduino as a laser DAC is going to be one gargantuan headache. I'm not necessarily trying to dissuade you, just making you aware for the shitstorm you're in for.

The projector will be powered by a 16V 4A laptop charger for wall power or 8*18650 Li-ions in series.

...Why?

My current plan is to use THIS

There's a lot of excess complexity here. You'll need an oscilloscope and function generator to test and refine this, or you'll be killing lots of laser diodes.



You've got your hand in seventeen cookie jars here. You really need to focus on ONE of these.

 

[Mattronium]

Re: My DIY laser projector project

You may find a lot of useful and helpful information
on Laser Projectors at PL... (Photonlexicon)

Jerry

I know, I'm going to post this on PL soon. But you can't edit a post after a day or so there. So I figured I'd post it here and get my formatting and pictures set up. Plus if I get it sort of together before SELEM then I might get some more advice there too.

I wish you luck, Matt. I'm hoping to learn from your mistakes before I tackle this kind of projector for myself. +rep.

Thank you.

You'd want to match power and divergence better than that. Also, a 462nm looks much better than 445 in a projector.

Yes, I am aware of the discrepancies. I wanted to include at least one multi-mode diode so that I could have some beam correction (all single mode would be too "easy"). I might upgrade to a 120mW 520nm PL520B later.

How are you going to get this software to interface with a microcontroller?
Arduino as a laser DAC is going to be one gargantuan headache. I'm not necessarily trying to dissuade you, just making you aware for the shitstorm you're in for.

I was hoping that I could work of off this (https://www.photonlexicon.com/forums/showthread.php/16567-Open-Laser-Show-DAC-(USB)). I want to keep it DIY and low cost. I'm no expert at this, so I appreciate any suggestions. I guess I could use an sound card DAC, but I was hoping for something more "mod-able".

There's a lot of excess complexity here. You'll need an oscilloscope and function generator to test and refine this, or you'll be killing lots of laser diodes.

Well I do have access to an oscilloscope. Could you be more specific by what exactly is excessive? I was trying to get a analog controllable CC driver with bias current and no "idling" current. If there is a better way of doing this I'm all ears. I did test a super simple mock up with just the three main op-amps for a quick test. When fed a square wave there was a significant spike on the rising edge, but I did not have any filters across the laser diode (or LED).

I'm simply using a laptop charger for the PSU is because I have lots of them. And the reason that I want to be able to run the projector of off a battery bank is "because I can", and I think it would be need to not have to plug the projector in for quick demos. Although, with space concerns, the battery idea will likely be the first to go .

What can I say, I do things not because they are easy, but because they are hard.

 

[Cyparagon]

Re: My DIY laser projector project

Could you be more specific by what exactly is excessive?

You can do it with one input voltage and one op amp.

I was trying to get a analog controllable CC driver with bias current and no "idling" current.

bias current and "idle" current are the same thing. Can you reword that?

When fed a square wave there was a significant spike on the rising edge, but I did not have any filters across the laser diode (or LED).

STARTING with a poor waveform and trying to filter it out at the last stage will decrease your bandwidth substantially. A proper driver should need nearly no filtering on the output.

I'm simply using a laptop charger for the PSU is because I have lots of them.

Okay, but nothing can run directly off of 16V in the projector you've described.

I want to be able to run the projector of off a battery bank is "because I can"

Right. But more specifically my question is why 30V on the battery? That's incompatible with the scanner power, the laser driver power, and the 16V input charger.

 

[Mattronium]

Re: My DIY laser projector project

You can do it with one input voltage and one op amp.

That is a great point. The two op-amps basically act as an overly complicated voltage divider. I'll have to fix that. :thanks:

bias current and "idle" current are the same thing. Can you reword that?

I was trying to get the laser diode current to be zero with an signal input of zero, while still having the bias current on for all other values.

I believe I need to bias to make the input and output linear in relation. EDIT: If I have a circuit with simple, straightforward biasing, then when the laser diode is set to "zero" the bias current will still be on. And so there will still a little bit of light. Is that explanation better?

Okay, but nothing can run directly off of 16V in the projector you've described.

Right. But more specifically my question is why 30V on the battery? That's incompatible with the scanner power, the laser driver power, and the 16V input charger.

I was planning to have a LDO regulator for the +15V for the scanner, a buck for the diode drivers. and an inverting driver for the -15V for the scanner. The reason I decided on 8*li-Ions for batteries is because when I used only 4 in series the voltage drop to 15V at 1-2 amps draw. Even using two 16V battery packs in parallel I think the voltage would drop too much for the +15V to the scanners.
When the battery is connected I'll have a switch for a buck driver to give the +15V. I guess using 5 Li-Ions in series should give enough voltage, I'll have to check to see how that'll work.

 

[Cyparagon]

Re: My DIY laser projector project

laser diode current to be zero with an signal input of zero

But then when the laser diode is set to "zero" the bias current will still be on. And so there will still a little bit of light.

Is that explanation better?

No. You've just contradicted yourself.

The reason I decided on 8*li-Ions for batteries is because when I used only 4 in series the voltage drop to 15V at 1-2 amps draw

So your reasoning is "Quantity X did not work, so clearly we DOUBLE the quantity." I hope you don't live the rest of your life like this. That's deadly.

 

[paul1598419]

Re: My DIY laser projector project

I'm guessing what he is trying to say is the bias current is minimal while his "input signal", or triangle, square, PWM wave current is not on. I'm not sure, but that is my best guess.

 

[Mattronium]

Re: My DIY laser projector project

I'm guessing what he is trying to say is the bias current is minimal while his "input signal", or triangle, square, PWM wave current is not on. I'm not sure, but that is my best guess.

Right.

When the input signal is zero, the output current is zero.
When the input signal is greater than zero the bias current will be on.

Like this (Circuit Simulation Link)

 

[Grix]

Re: My DIY laser projector project

Software: Whatever free software I can find to play with.
So, HE laserscan and LFI.

http://pages.bitlasers.com/lasershowgen/

It supports both the DAC solutions you mentioned you were considering (OLSD and sound cards)

 

[diachi]

Re: My DIY laser projector project

Right.

When the input signal is zero, the output current is zero.
When the input signal is greater than zero the bias current will be on.

Like this (Circuit Simulation Link)

Your terminology is off.

Bias current set is the output current when there is 0V signal applied. You set this to just above the diodes threshold, so you get just a slight bit of lasing going on, tiny amount of power. The LD is forward biased at that point.

You also set the modulation current, which is the current supplied when you apply a 100% modulation signal (5V for ILDA). You want to set this to the maximum current for your diode so that you get full output at 100% signal.

If you set the current at 0V modulation to 0A then your modulated output won't be as nice.

 

[paul1598419]

Re: My DIY laser projector project

Your terminology is off.

Bias current set is the output current when there is 0V signal applied. You set this to just above the diodes threshold, so you get just a slight bit of lasing going on, tiny amount of power.

You also set the modulation current, which is the current supplied when you apply a 100% modulation signal (5V for ILDA).

Yeah, This.^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

[Mattronium]

Re: My DIY laser projector project

Your terminology is off.

Bias current set is the output current when there is 0V signal applied. You set this to just above the diodes threshold, so you get just a slight bit of lasing going on, tiny amount of power. The LD is forward biased at that point.

You also set the modulation current, which is the current supplied when you apply a 100% modulation signal (5V for ILDA). You want to set this to the maximum current for your diode so that you get full output at 100% signal.

If you set the current at 0V modulation to 0A then your modulated output won't be as nice.

Oohh, I see, thanks for pointing that out.

What would be the right terminology?:thinking:


Anyways, so slight update: I got some 1" thick Al pieces for the diode mounts. I have quite a few parts and pieces on the way that I'm waiting for. Also, I'm going to use music wire 0.28 mm to make springs to replace the o-rings that I was using for my prototype mirror mount.

 

[Mattronium]

Re: My DIY laser projector project

Update: Machined first test diode mount block. 1.5" x 1" x 0.75"

Working on winding some extension springs for the mirror and dicro mounts. Using 0.279mm music wire. One guitar-length string gives me about 7 springs. I'll need ten springs minimum.