[TriEmbed] Arduino Due dac0 issues

[Alex Davis]

Anyone familiar with using the Arduino Due? I am using one in the project published here http://www.nutsvolts.com/magazine/article/the-arduino-graphics-interface-part-1 <http://www.nutsvolts.com/magazine/article/the-arduino-graphics-interface-part-1>

It uses the Due's DMA-driven DAC outputs to produce signals to drive an XY graphic display. The circuit is very simple. Just buffers on the inputs and a sample/hold blanking arrangement to smooth out the DAC output.

I find that the circuit manages to destroy DAC0 output, though I can not discern why. Each DAC feeds a 10k/4.7k voltage divider before the buffer inputs; this should not be an excessive load. I bought the board from Nuts and Volts so I haven’t made a breadboard mistake. There is no measured low resistance on the DAC0 or DAC1 inputs on the board, nor is there any voltage offset there.

If v/div is cranked up high enough, the output can still be seen on DAC0, so I think the DAC is actually fine and the issue is perhaps an output transistor or even a multiplexer.

Using a very simple for loop instead of the Nuts and Volts code does not fix the problem once it happens.

void loop() {
 for (int i = 0; i <256; i++) analogWrite(DAC0,i); 
 for (int j = 0; j <256; j++) analogWrite(DAC1,j); 
}

Anyhow, there are some search hits online which suggest there is some sort of fragility with the output for DAC0. An ATSAM3X8E bought domestically costs almost as much as a complete Chinese knock-off Due, so I think I will not be attempting to replace them. I’ve ruined two already, so I think this project is going to go into the trash so that I may move on with my life, so to speak. Nuts and Volts forums are a ghost town and have no info on the project. Sometimes it may be best to just take a hammer to things so that you may prevent yourself from throwing away more time on it.

If someone has a Due they can stand to sacrifice, I would be interesting in seeing if the problem can be solved by feeding the board DAC inputs with 10K resistors instead of jumper wires from the DAC output pins. It really should not be that fragile, but maybe it is.

Alex
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