I think to use 2 output pins on Arduino, call them D1 and D2. DAC will have 12+ and 12- supply voltage. This is only for the ignition pulse. The pulse width should change with rpm, I think I remember it does that now, and the time between the 2 pulses should change in relation to barWidth.
when all input pins of DAC get a 1 (+5v) the DAC output +12v (if powered by +12)
when all input pins of DAC get a 0 (gnd) the DAC output -12v (if powered by -12)
when pin5 of DAC get a 1 and others got a 0 the DAC output 0v
Then 2 pins of arduino are enough to get pos and neg square pulses and zero volt.
Say you connect D1 to pin 5 and D2 to pins 6,7,8,9,10,11,12 together
Thanks, Tom
