Open Source/Freeware Budget USB DAC

[chad]

Hi, Looking great!!

Did you use eagle for the schematic by chance?

I only ask because I have eagle and I would like to build a board and follow along with you guys. I have all of the pic junk also.

" 5) DMX512 Input (If possible)" LOL Thanks!

I have had some dmx laser head accessory stuff on the drawing board for a while..

chad

[Paul_B]

Hi, Looking great!!

Did you use eagle for the schematic by chance?

I only ask because I have eagle and I would like to build a board and follow along with you guys. I have all of the pic junk also.

" 5) DMX512 Input (If possible)" LOL Thanks!

I have had some dmx laser head accessory stuff on the drawing board for a while..

chad

Hi Chad,

Thanks....I used Orcad to capture the schematic.

As for the DMX512 input, I am hoping there is going to be enough code space for DMX512 comms (In and Out).

Cheers
Paul

[mixedgas]

3 reccomendations:
in no particular order.


assuming you dont want to go broke with world class cambridges:

SCANCO30s
a pair is here from the distributer, Dave in OZ, hes a member here so you can work out things directly if ebay is not your thing
ebay #
260181991499
You might say I'm a little biased since I won a pair at FLEM.

DT40s by Jian in China also have a strong reputation and I have seen nice test patterns and graphics at FLEM.
Jian is also a member.


Eye Magics from New Method Lasers in Florida are great too, and are awesome for tight graphics. I have used two pairs of them for like 3 years now. Fred hangs out here too.

Steve Roberts

[carmangary]

For 30K scanners I recommend contacting Darry at laserpic ( www.laserpic.com ) to see what he can do for you.

[shobley]

Are there any schematics on the thread? I'm looking for an output stage to convert my 0-5v DAC output to the full -/+ 5v differential needed to run galvo amps.

Quick question - if my galvo has a floating ground, and my DAC has a ground at -10v to my galvo, how would I deal with this?

Get a better PSU??


Steve

EDIT:

Just found the schematics - will an SSM2142 do the conversion for me? As far as I can tell the output from the MCP4822 is 0-5v just like my DAC...

[Paul_B]

Are there any schematics on the thread? I'm looking for an output stage to convert my 0-5v DAC output to the full -/+ 5v differential needed to run galvo amps.

Quick question - if my galvo has a floating ground, and my DAC has a ground at -10v to my galvo, how would I deal with this?

Get a better PSU??


Steve

EDIT:

Just found the schematics - will an SSM2142 do the conversion for me? As far as I can tell the output from the MCP4822 is 0-5v just like my DAC...

Hi shobley,

I have just finished getting the first part of the embedded code working for this USBDAC working, I did some measurements and the SSM2142 provides a differential output, with the MCP4822 loaded with a value of 0xFFF (full output - 12bit) the SSM2142 has an output of approx. 9Vp-p, the outputs did vary slightly between the X,Y,R,G and B outputs (approx. 0.05 - 0.09V). The MCP4822 at full output is just over 4V not 5V. These reading were taken with the SSM2142 driving into my Fluke multimeter (high impedance) - no scanner input load.

I need to know from the guru's on here, what is the maximum a scanner amp/analog modulation input can handle? Is 9Vp-p to much?

I have a working embedded frame-work working - I will post it in a couple of days. I just need to clean up the code a bit and also include some comments.

At the moment the USBDAC is completely under PC control - no buffering. All I have to test with at the moment is a demo GUI I knocked together quickerly with some sliders on (one for each MCP4822 output), the updating of the DAC values is in a 1mS timer. The responce seems good. I will need some help with displaying a full frame to test this DAC properly.

I will provide all source files for embedded code, bootloader (PC and embedded) and my simple DAC channel tester as well as the API.

Cheers
Paul

[shobley]

Good to know - so just so I understand this correctly, when you load the DAC with 0 - do you get -9v differential, or just 0v?

...or is there another stage to convert the output from a DC to AC waveform?

[carmangary]

Differential scanner amps want +-10v which means +-5v & -+5v simultaneously on the differential outputs.

Single ended ones just want +-5v w/ respect to ground.

[shobley]

So.....

Is that what it does?

[Paul_B]

Good to know - so just so I understand this correctly, when you load the DAC with 0 - do you get -9v differential, or just 0v?

...or is there another stage to convert the output from a DC to AC waveform?

Hi,

When 0V is applied to the input SSM2142 it outputs 0V and as the input increases you get a positive voltage on pin7/8 (these need to be shorted together) and the same value but negative voltage on pin1/2 (these also need to be short together). These are readings are with respect to GND/0V.

eg: 1V input - pin1/2 -1V, pin7/8 +1V (2Vp-p) output.

Don't forget the 100nF capacitors as close to pin5 and pin6 these are critical. I did a test without these connected and the noise level was huge.

Cheers
Paul