Open Source/Freeware Budget USB DAC

[drlava]

Ok, glad we've settled on some good raw hardware. Here is something to consider for the output amps:

The official ILDA spec, at least what I read from the excellent laserFX site, specifies that the X and Y signals are delivered with a pair of differential outputs each limited to a +/-5V swing with respect to the ground pin for a total peak differential voltage of +/- 10V. Similarly, the color and intensity signals are to be differential 0 to 2.5V and 0 to -2.5V outputs with respect to the ground pin for a 0 to 5V differential swing. However. Almost every analog laser uses single ended 5V (with respect to ground) input, but the spec only allows for max 2.5V with respect to ground.

I propose that for the X and Y outputs, we stick to the standard and just have plain-jane output amps with +/- 5V max (with respect to the gnd pin) signals on the outputs, however with the color and intensity lines, we make use of an active balanced transmitter setup. The active balanced transmitter setup will produce a 5V swing using +/- 2.5V differential lines when connected to a projector that accepts differential inputs, however when connected to a projector that grounds the -R,G,B, or I signals, the active balanced transmitter will develop the 5V differential on the +R,G,B,or I lines. The result will maintain noise cancellation for projectors that make use of it, while at the same time work well with projectors that don't make use of it.

An example of an active balanced transmitter for audio is on this page:
http://sound.westhost.com/project87.htm
and here
http://sound.westhost.com/balance.htm

[heroic]

[balanced output drivers]

I dig it, let's do that.

What's good for schematic capture these days? Bonus points if I can run it on a Mac. I'd use Orcad but I'm guessing most people don't have a license for that...

[cfavreau]

Eagle is big in the DIY world. See Linux-Laser project for a nice differential output setup I think. I think it uses TL084's which are inexpensive and work well.

[FourDee]

Jup, you forgot a few things in you list mixedgas ...

• DC-DC converter
• Dacs that can output positive / negative (I don't know which one you settled one but you may want to check that)
• Alternatively, you could use an extra opamp with an offset + gain of 2
• And then you'd just need two more opamps to form the differential output (inverting + non-inverting amps with gain of (-)1)

[shrad]

may I point out this controller?

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3609

this is a LQFP package, but its performances are TOP!

has ethernet with everything needed to do UDP streaming, everything for math processing, 32bit, 80Mhz and the list goes...

the most interesting is that it is available as free samples from maxim

but most of the deal is that it is fully JAVA programmable, with a java virtual machine in it when you receive it, you just have to plug it on your network to start programming

again, there's a serial port which could easily take care of several Mbps for FTDI use

[riyalasers]

to Steve about components:

If you will use DAC without internal reference voltage - you should use separate chip for it (REF195 for example)

Next...
Your device will work by USB. So it can't be OEM. It means that you should spent additional money for:
- enclosure;
- mechanics work for enclosure (cutting windows for connectors and LED );
- printing.

And..
It will powered from USB?
If no - add power supply cost...

Ihor

[heroic]

may I point out this controller?

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3609

this is a LQFP package, but its performances are TOP!

And you can't get it for love nor money. Maxim's lead times are legendary; plus, Atmel have been good to me in the past. It's either Atmel or ARM for me, thanks. I've played the my-product-is-now-suddenly-dead architecture game one time too many.

to Steve about components:

If you will use DAC without internal reference voltage - you should use separate chip for it (REF195 for example)

A three-pin regulator (which we need anyway) has worked very well for me in this application.

Your device will work by USB. So it can't be OEM.

That makes no sense whatsoever.

[shrad]

the problem with 3-pins regulators (at least 78 and 79 series) are not so accurate, temperature dependant, tend to oscillate, and many more issues

zener voltage references are far better, stable and so, but still temperature dependant

there are voltage references based on zener but with thermal compensation for some cents, I think, which would avoid to have to adjust each DAC voltages by hand to compensate for differences

[heroic]

the problem with 3-pins regulators (at least 78 and 79 series) are not so accurate, temperature dependant, tend to oscillate, and many more issues

Modern three-pin LDO regulators contain precision bandgap references which are very accurate and stable.

[mixedgas]

[QUOTE=heroic;96746]And you can't get it for love nor money. Maxim's lead times are legendary; plus, Atmel have been good to me in the past.

Yeah, I'm trying to source 4-6 pieces of a Max part that had a lifetime of four years and cost 1.50$ when new. I just got quoted 35.00$ each from a chip broker, minimum order 10. He bought the entire remaining lot at the "end of life" announcement, and would have 40 left in stock if I ordered the 10.
Most chip makers idea of a EOl quanity is 40,000.

Maxim is FABLESS on a lot of their parts, and when a fab changes technology Maxim does not redesign. But they make some of the most groovie unobtainium in the world.

Yet AD and National still source stuff that is pushing 40 years of production.

Of course National's big mistake was discontinuing the LM3909 and they learned from the backlash over that.

Steve