Reverse R-2R DAC for Musical Keyboard Input

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harveyf2801

Joined Nov 12, 2021
5
Hi folks,
A while back I was struggling with this concept I had, of reversing the R-2R DAC structure so that it works as an ADC converter from my musical keyboard inputs into a binary word. My issue was the switches used are SPST so when they were off, the value was floating and giving false values.

However I recently found a solution to this by using inverters as seen in this diagram (to the right): https://tinyurl.com/yfmpl4e5
In theory this works on the simulation. The issue I now have is that the inverter always outputs a small voltage of 0.1V on LOW and when it’s meant to output a HIGH state it gives just under 5V. Unfortunate this causes an inaccuracy on the binary word… was wondering if anyone had any ideas of how to improve this?
 

Papabravo

Joined Feb 24, 2006
21,010
Use analog switches with very low Rds(on) to switch a buffered precision reference and ground to the appropriate points.
 
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