# How to add CV control to a knob on existing module **URL:** \ **Category:** DIY STUFF\ **Created:** [June 8, 2021, 10:09am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634 "2021-06-08T10:09:32Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![amba](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amba](https://lookmumnocomputer.discourse.group/u/amba)\ **Post date:** [June 8, 2021, 10:09am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/1 "2021-06-08T10:09:32Z")
Hi, Recently exploring the amazing world of clocks/dividers and everything in between. I found something perfect for my needs and budget to generate polyrythms. the CLK from REBEL tech. which has three knobs that control 1.Master tempo 2. /8\* out 3. /24\* out. As this is on github : [GitHub - pingdynasty/CLK: CLK is a triple clock generator Eurorack module from Rebel Technology](https://github.com/pingdynasty/CLK) I was wondering if anyone would know how to add CV control either simply to the master tempo and for more complexity CV control to each knob with an input for each. And also wondering if there is a rule used for adding CV control functions to any form of existing control. Thanks in advance! Kind regards, Amba ---
**Author:** ![jaradical](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jaradical/32/12069_2.png) [@jaradical](https://lookmumnocomputer.discourse.group/u/jaradical)\ **Post date:** [June 8, 2021, 10:25am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/2 "2021-06-08T10:25:24Z")
From the schematic, it looks like the pots are driving pins of an ADC directly. So, if you wanted CV control as well as the knobs working, you would need to condition your CV input to be in the range of 0-5V, then probably sum it the output of the pot, ensure that _that_ signal doesn’t go outside the 0-5V range and then plug it back into the ADC input. Cheers ---
**Author:** ![BlackDeath](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/blackdeath/32/7644_2.png) [@BlackDeath](https://lookmumnocomputer.discourse.group/u/BlackDeath)\ **Post date:** [June 8, 2021, 10:26am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/3 "2021-06-08T10:26:38Z")
Generally, you can use a H11F1M or roll your own vactrol with an LED and an LDR. You won’t get v/oct, but you’ll get something, and then you can attenuate/range to get the precision you need. ---
**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\ **Post date:** [June 8, 2021, 10:49am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/4 "2021-06-08T10:49:40Z")
> [@jaradical](#): > > From the schematic, it looks like the pots are driving pins of an ADC directly. > > So, if you wanted CV control as well as the knobs working, you would need to condition your CV input to be in the range of 0-5V, then probably sum it the output of the pot, ensure that _that_ signal doesn’t go outside the 0-5V range and then plug it back into the ADC input. This seems to be the way to go in this specific case. Take the CV in, pass it through an attenuator, then sum it with the offset pot. Clamp this between 0-5V (very important!!) using zeners, schottkys or by using rail-2-rail opamps (eg MCP600x), and connect to the PIC. ---
**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\ **Post date:** [June 8, 2021, 10:54am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/5 "2021-06-08T10:54:22Z")
Also see: > [@Adding CV to existing circuits](https://lookmumnocomputer.discourse.group/t/adding-cv-to-existing-circuits/1305): > > hey friends, I am working on a project (BD++) and am wanting to add CV to a parameter usually controlled by a potentiometer. here is the existing circuit: [vactolQ1] I understand since this pot is acting as a variable resistor it can be replaced with a cv source via vactrol. Is it possible to just sum them together, pot and CV? something like: [vactrolQ] is there an easier way to do this without using vactrol? opamps? (…while I’m deciding if I should merge these threads or not 🙂 ) ---
**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\ **Post date:** [June 8, 2021, 11:00am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/6 "2021-06-08T11:00:32Z")
Yeah, same question, quite different cases. In the thread you linked the pot is wired as a variable resistor, while here it’s just a voltage divider providing a CV. The current case is quite a lot simpler, as effectively, there is already CV control. ---
**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:** [June 8, 2021, 11:29am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/7 "2021-06-08T11:29:12Z")
But “same question”, or at least essentially the same topic title. Someone in a similar situation looking for answers would have to read both topics to know which one was relevant to their problem. You could either merge the topics for a single place to find any information about adding CV, or change the titles to clarify which specific problem each is about — though that would be hard to do in a short title. I think merging makes sense. ---
**Author:** ![amba](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amba](https://lookmumnocomputer.discourse.group/u/amba)\ **Post date:** [June 19, 2021, 12:54pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/8 "2021-06-19T12:54:58Z")
Thanks so much for all the answers. I am really a beginner so all of this sounds a little difficult to wrap my head around. I will go have a look in the other topic, see if I can already practice putting cv control over a VCA or something. Or would you have a stripboard image by any chance? ---
**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\ **Post date:** [June 19, 2021, 1:12pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/9 "2021-06-19T13:12:35Z")
Here’s a small sketch. The first opamp sums the pot value with the CV, but its output is inverted. The second opamp re-inverts the signal. You might want to add an attenuator to the CV input. Google any words you don’t know, and soon you’ll learn. ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/f/f96c4650224046a53ccce6bd2670b8cd5fd326f4.jpeg) ---
**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:** [June 19, 2021, 1:45pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/10 "2021-06-19T13:45:27Z")
While @TimMJN was posting that I was drawing up something similar: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/7/70f0423b4fe5f7250b357c79a6d11aaf621b877d.png) I put in an LM358 but the MCP6002 might be better. I put a Schottky diode and series resistor on the line to the microcontroller to protect against overvoltage because the LM358 isn’t rail to rail so uses a +12 V supply. With the MCP6002 powered from 5 V you wouldn’t need them. I used 10k resistors in the second op amp stage to reduce noise, and showed bypass caps on the op amp supply pins. ---
**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\ **Post date:** [June 19, 2021, 1:51pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/11 "2021-06-19T13:51:01Z")
Great minds think alike! …Yet fools seldom differ… PS wouldn’t this configuration have trouble going down to 0V? ---
**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:** [June 19, 2021, 1:53pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/12 "2021-06-19T13:53:10Z")
The LM358 goes 0 to V+ - 1.5 V. I don’t see why it wouldn’t go to 0. ---
**Author:** ![TimMJN](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmjn/32/15227_2.png) [@TimMJN](https://lookmumnocomputer.discourse.group/u/TimMJN)\ **Post date:** [June 19, 2021, 1:54pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/13 "2021-06-19T13:54:46Z")
okay, good! I wasn’t sure if it would reach 0V when its negative rail is GND. Cheers! ---
**Author:** ![amba](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amba](https://lookmumnocomputer.discourse.group/u/amba)\ **Post date:** [June 19, 2021, 1:55pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/14 "2021-06-19T13:55:29Z")
Great ! Thanks to all for this input! I will try and strip board this with a perf board version of the CLK module with the github schematics before trying the new module that should arrive next week. ---
**Author:** ![amba](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amba](https://lookmumnocomputer.discourse.group/u/amba)\ **Post date:** [June 25, 2021, 7:40am UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/15 "2021-06-25T07:40:16Z")
As the weekend is coming I have all. my builds and pieces ready to experiment. I don’t know if this is the right section. I wanted to know if I could add a jack(CV) input with or instead of a button/potentiomètre? To give an example, Sam’s Big button Sequencer, could the button be replaced simple with either the jack being wired like the button or like the circuit above. I also saw this circuit the puts the jack to ground and for the CV inputs(replacing the buttons) a 1n4148 + resistor? I wanted to avoid vactrols as I dont have everything necessary for this weekend. Thanks on advance for all the help! ---
**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:** [June 25, 2021, 5:40pm UTC](https://lookmumnocomputer.discourse.group/t/how-to-add-cv-control-to-a-knob-on-existing-module/3634/16 "2021-06-25T17:40:41Z")
Not sure what you’re asking but the Big Button already has a trigger input jack that allows an external trigger to do the same thing as the button.