# Arduino CV inputs / offsets

**URL:** <https://lookmumnocomputer.discourse.group/t/arduino-cv-inputs-offsets/2326>\
**Category:** DIY STUFF\
**Created:** [November 19, 2020, 12:54pm UTC](https://lookmumnocomputer.discourse.group/t/arduino-cv-inputs-offsets/2326 "2020-11-19T12:54:34Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![sebastian](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/sebastian/32/39_2.png) [@sebastian](https://lookmumnocomputer.discourse.group/u/sebastian)\
**Post date:** [November 19, 2020, 12:54pm UTC](https://lookmumnocomputer.discourse.group/t/arduino-cv-inputs-offsets/2326/1 "2020-11-19T12:54:34Z")

</div>

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](https://mutable-instruments.net/modules/braids/downloads/braids_v50.pdf) and one in [Grids](https://mutable-instruments.net/modules/grids/downloads/grids_v02.pdf).

Braids:

 ![Screenshot from 2020-11-19 13-48-39](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/b/bbe05eb4644344c90ddbe4122b595ed8bf33be1f.png)

Grids:  
 ![Screenshot from 2020-11-19 13-49-40](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/1/1aec05b48a429b523f334c708ecf1530a5e7c16d.png)

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](https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAXKQUgCgA3EYwkFBF58MFKcEAFkgVeQmAloBzJizYcWuflFoAnaVx5hiG7rzDw4K8FvD9F2bCzCnebeLQDuIc5evOjPOo80br38BhZPNVl3VnYlL2M0PFCQugBDUL83PxiwJABadOR9UVh4PRRiQRQ8U34EcxLdXNpE0xjoiij8EDTM7L1ckAyYfQqEPEJKSrYLPAwiGv1aAHkQYZlWwjxG1tEHZp4mxdZ1w2wEDWN+MEtjIVsDRwbWFEU-OM3T855bvzpVd9Kt8B+hGh2G78NI-d4XTYIYzcGJQ7b7L7YHhucZOCw2WpgSZOI5o+SQMzooTkLKiHp6ETQJAANQA9gAbAAu8QkAFNNodkejUW4gvwkXiBGdQkFOaEUhDItpjj5FAknATeLchO1yUguvoen1+qd0hgEPwMPhDrhyEINQZVFZFBlCIp7kJbXKcnYrdYsjJBOTAi7LSYzNsvQLzbUpApwPjFCClPMQWSEDoyXQsdKenaFjb08TeEgk1SQHSmSz2QAlNQejPekQCR25yniVRIx3pl5p52A64CPBk5URIUsJ0CaMbRxNtsKm3C0WKisO8fTyeex1Tjkz4Vz4ObMA6QfW+db93CmFVoKcCvHitBPcCzjbjy0Wm8LM14iwqCwNg2XjYB-IStCQRX2EGAIFA38in-F83xA1hwFoIA) 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? 🙂

---

<div class="post-metadata">

**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\
**Post date:** [November 19, 2020, 2:04pm UTC](https://lookmumnocomputer.discourse.group/t/arduino-cv-inputs-offsets/2326/2 "2020-11-19T14:04:38Z")

</div>

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.

---

<div class="post-metadata">

**Author:** ![sebastian](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/sebastian/32/39_2.png) [@sebastian](https://lookmumnocomputer.discourse.group/u/sebastian)\
**Post date:** [November 20, 2020, 11:27am UTC](https://lookmumnocomputer.discourse.group/t/arduino-cv-inputs-offsets/2326/3 "2020-11-20T11:27:36Z")

</div>

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?