Review of Arduino DAC solutions

Posted on Feb 5, 2014

An analog output for my Arduino. The most common way to build a DAC is to use a R-2R ladder circuit. However, this DAC has no output buffer, which would make this circuit a bit more reliable and working with all kinds of loads. For the best results, you should use an output buffer in the DAC. The buffer separates your R-2R ladder from the load you connect it to and makes the result non load dependent.

Review of Arduino DAC solutions
Click here to download the full size of the above Circuit.

Here`s maybe the best tutorial I`ve seen for a R-2R DAC with an output buffer. It uses a common LM358 operational amplifier that can be driven from single supply. Note that in order to get the full output range to work with this circuit, you need to have a higher than 5V supply for the LM358. Of course, another way to get around this problem is to use a 5V supply but put a simple voltage divider in front of the op amp. Then you`ll get lower than 5V output but don`t lose fidelity. A very clever solution utilizing the integrated pullup resistors on the Atmega chip. You need only 1 resistor and as many output pins as you want bits. The output is a bit crude but 500kHz could be reached. The internal pullups are specified to be minimum 20kohms and maximum 50kohms so the result might not be the most accurate. This design uses only two output pins, and the circuit is fairly simple, utilizing an op amp. The max settling time is 20ms, which is way too low for audio output. But the settling time could be enhanced with a circuit modification. Of course, you can also use the PWM outputs to get an analog output signal from the Arduino. Just put a low pass filter after the PWM output to get a nice & smooth output with a frequency range up to 16kHz, according to this Lab3 experiment. This is a good explanation on how to combine two PWM outputs in order to double the bit resolution. So combining two 8-bit arduino PWM outputs you can get a...

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