Designing a differential ILDA Output for Arduino

[Wondergy]

For science education, I designed a "laser oscilloscope." It looks like this: http://wondergy.com/sound/

It is built on an Arduino which "sweeps" the laser across, and triggers on sound levels. The first version only uses the non-inverting side of the ILDA connector. I run 0-5+ (up to 10) volts for x and y, and it works well with one particular projector, which also only uses the + side of the connections (built by Technological Artisans some years ago.)

I really want to make this portable among ILDA projectors, so it will scan the full XY range. I assume this means it needs to go +5 to -5, and have corresponding inverted outputs. This is where I get stuck.

It looks like this is best achieved through inverting op-amps, but all of the schematics I've found simply assume there's a +12v, 0, and -12v line available in the circuit. Where is everyone getting these -12v's from?? I've got a 12V power supply running the Arduino and I would like it to run the shield I'm building too. I see lots of USB DACs now, which would only have 5v to start. I can't find schematics that get me all the way from the 12v supply to a full ILDA output. I'm trying to keep it simple, component-wise.

Not sure if this is a novice or advanced questions. I feel like the more I learn the less I know. Please help?

Here is one of the schematics I found, which made sense, but left me clueless how to supply power to it.

[mixedgas]

See:

http://www.photonlexicon.com/forums/...ILDA-STANDARDS

The recommended ILDA driver schematics are there. Click on the middle PDF and scroll towards the back.

What your looking for is a Dual Output DC-DC converter, preferably a low noise one.

For USB power You'll need 5V converted to +/- 12V at 20-30 mA per rail.

Make sure you put a 100 uF filter cap on each rail to ground. Then place a 0.1 uF ceramic bypass cap on each rail to ground.

Marginal current but it should work:

http://www.digikey.com/product-searc...=0&pageSize=25

Past experience indicates that you should consider stocking spares of tiny DC-DC converters when on the road. The USB environment is rather unforgiving.

1 amp, +/-12V DC output, 110VAC powered power supplies are about 24$ and would be a better deal.

Steve

[Wondergy]

Thanks! The ILDA docs seem to also assume I have the +- voltage available. I don't need it to be USB - I'm quite happy to use a 12V power supply, if there were a way to convert it to -12V. It plugs right into the Arduino Uno, for easy split off to everything else. I'm trying to build this today/tomorrow, as version 1 just went kaput on the road, and I need to send something out to him that works shortly, and need to test it with truly ILDA compliant projectors here. I'm sitting right next to a radio shack, and don't see anything in stock that will work. Is there a simple way to make this work?

[mixedgas]

I'm sitting right next to a radio shack, and don't see anything in stock that will work. Is there a simple way to make this work?[/QUOTE]

Unless radio shack started stocking regulated 12VDC wall warts again, of which you need TWO, there is only one way...

Attached is schematic for poor grade, regulated, weak +/- 12V power supply from radio shack parts. Since they stopped stocking LM7912 negative regulators, this has to use two isolated 12VAC transformers.

The attached diagram is a "Absolute Emergency" device. I'd never recommend this scheme these days, but it should work quite well til you can do better in a week or so.

The 12VDC outputs need one amp fuses between them and the opamps (not shown)

It goes without saying that this must be built using appropriate techniques for 110VAC powered devices.

Steve

[mixedgas]

RadShack Compatible Offset Board.

For emergency use...


Steve

[Wondergy]

Wow, thanks for the advice! Did you just make these drawings? Thanks indeed!
You mentioned using two 12v supplies - honestly that sounds like the most attractive concept, as I have a few 12V supplies like these laying around. I didn't think I could simply use two. Is that possible?

[mixedgas]

Yes, in theory you can stack two of those really cheap Chinese supplies.

Steve

[dave]

You should have a look here: http://www.fab-favreau.com/index.php/Main/OLSDRev4