7-Bit DAC Demo

I've come up with this exercise specifically with analog electronic music synthesizers in mind. The modules comprising such an affair, as a rule, follow a one volt per octave control scheme. Thus, this circuit spits out an analog voltage which doubles for each increase in octave. Being a 7-bit DAC, then, that's enough to cover a 128 note scale, considerably more than a piano.

But of course, it would be useful for many other applications, especially since it is quite accurate. (It has to be accurate for musical instruments to avoid sour notes which the human ear is quite sensitive to). You'll note in the schematic the presence of a trimmer which allows you to precisely set the scale factor.

Here's what to expect. A pushbutton, S2, steps the output voltage along. Now if toggle switch S1 is closed, then each press of the pushbutton increases the output by 1/12th of a volt, there being twelve notes to an octave. On the other hand, if S1 is open, then each press of the pushbutton increases the output by one volt; in this case, you're jumping by one octave at a time. The range is 0V to 10V.

In the photograph, above, you'll note that I'm monitoring the results on a multimeter. When the picture was taken, I was currently in the middle of the scale, at 5V.

Even more useful would be to test it with a VCO (voltage controlled oscillator) from a music synthesizer, and let your ears weigh its merits.

I've been using the DAC0800 for over thirty-five years now and have always found it be a champ. Indeed, you can expect some more designs using it in this collection of exercises.

Click to get the source code.
Click to get the schematic PDF.

Next Project: 8-Bit DAC via PWM

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