DAC as digital attenuator

[Jan Lichtenbelt]

DAC will mostly be used to convert a byte or integer into an analogue signal. The analogue signal can mostly be any value between the power supply voltages 0 and 5 Volt. However, instead of the 5V also an external Vref can be chosen. So far it sounds familiar.

But you know, Vref can be a signal between 0-5Volt, not only dc but any signal. Most DACs are just a number of resistances in series, see scheme. By changing the byte of the DAC Vref will be connected to one (or more) of the resistances with result that the Vref will just be attenuated at the output.

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I started with a sinus signal top-top between 0-5 Volt. In the two scope pictures you see both input (larger sinus) and output of the DAC (smaller sinus). Youtube movie shows the output as with variating of the byte value of the DAC (5 bits for 16F1847).
https://www.youtube.com/watch?v=1XD8VF9WPvQ

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P1070092_t.jpg (42.81 KiB) Viewed 5197 times

Jan Lichtenbelt

[Jan Lichtenbelt]

Please find the flowcode 7 attached.

DAC_as_Digital_attenuator_V1.fcfx

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Jan Lichtenbelt

[petesmart]

Very clever Jan.... Thanks for sharing

Best

Pete

[Benj]

I hadn't thought about using a varying signal into VRef+, great idea.

I guess you could use a similar approach for something like volume control. The DAC outputs the signal and you can use a pot to control the voltage to VRef which scales the output.

Very cool, thanks for sharing.