Arduino CV inputs / offsets

Hi, I was looking at how to input CV into an Arduino. I found two schematics, both from Mutable Instruments which are a bit different for the same application. I found the one in Braids and one in Grids.


Screenshot from 2020-11-19 13-49-40

In Grids, the output goes directly into an Arduino, while for the Braids it goes to an ADC (MCP3204).
I simulated the two in Falstad and it looks pretty much the same (after I adjusted R16 to 50k in the Grids to also have a max output of 2.5V)…
Could someone explain to me the difference and what would be preferable? :slight_smile:


In Grids there’s a single inverting stage. The positive CV (0 to 5 V) is summed with a negative reference to make a negative input so the output will be positive, as needed by the microcontroller. The software will have to deal with the fact +5 V corresponds to 0 V input, and vice versa. The Braids has two inverting stages, with -10 V summed at the second stage to make a positive or negative CV into a positive signal for the microcontroller — If I’m thinking correctly this early it divides ±10 V down to ±2.5 V and then applies a 2.5 V offset. So one avoids a second gain stage by turning 0–5 V into 5–0 V and one uses two gain stages to turn ±10 V (I think) into a positive voltage.


Thanks! In my simulation, however (you can see them in the link in first post) I see only the difference of “inverting”, like making -5V +5V to 5V 0V for the grids solution, while the braids one makes -5V 5V to 0V 5V, which is only a software problem then. For -10V 10V it is the same, in both cases I need to double the first resistor (R19 or R47) to get into the 0V 5V range (or 5V 0V). Am I missing something?