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Hi all,

I am currently working on a project that I need an adjustable voltage (3V, 3.5V, 4V, 4.5V) to feed in to the reference voltage input of the comparator. See the circuit diagram below.



I was surfing the forum and the playground from the Arduino website, there are few ways I can
achieve the DAC from the Arduino.http://arduino.cc/playground/Main/InterfacingWithHardware#adcdac

Using OpAmp
http://www.avdweb.nl/arduino/simple-10-bit-dac.html
R/2R Ladder
http://blog.makezine.com/archive/2008/05/makeit-protodac-shield-fo.html?CMP=OTC-0D6B48984890

Here are my problems.
1) Which method do you recommend for my application? R/2R Ladder or the one using the op amp?
2) Can the ADC output an DC voltage (0 to 5V) ?
3) Am I using the PWM output pin to achieve the process of DAC?

Best Regards,
tayip
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Since you only have 4 values a few resistors would suffice.  You'd have to work out suitable values - connect one to Vcc and three others to three pins, each acts as a voltage divider if that pin is low, and is out of the circuit if than pinMode is INPUT.  the divider ratios need to be 3.5/5, 4/5 and 4.5/5...

No the ADC doesn't output anything, its reads voltages only.

With PWM you would have to low pass filter the waveform appropriately, but you do get 256 output levels.
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