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Pot override by CV input
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Pot override by CV input
pfzzz
I'm trying to get CV attenuated by a pot and if not connected then just take the pot value to be used in a microcontroller arduino basically!

I'm reading this schematic from mutable which has the same thing but I'm having difficulty understanding the schematic part especially with -5 ref and why it's -5, it accepts -+5v

https://mutable-instruments.net/modules/branches/downloads/branches_v4 0.pdf

If someone could explain what's happening would be great for me to understand,

Thank you
ixtern
pfzzz wrote:
I'm trying to get CV attenuated by a pot and if not connected then just take the pot value to be used in a microcontroller arduino basically!

I'm reading this schematic from mutable which has the same thing but I'm having difficulty understanding the schematic part especially with -5 ref and why it's -5, it accepts -+5v

https://mutable-instruments.net/modules/branches/downloads/branches_v4 0.pdf

If someone could explain what's happening would be great for me to understand,

Thank you

Because input Op Amp inverts voltage from -5V to +5V.
Mungo
pfzzz wrote:
I'm trying to get CV attenuated by a pot and if not connected then just take the pot value to be used in a microcontroller arduino basically!

I'm reading this schematic from mutable which has the same thing but I'm having difficulty understanding the schematic part especially with -5 ref and why it's -5, it accepts -+5v

https://mutable-instruments.net/modules/branches/downloads/branches_v4 0.pdf

If someone could explain what's happening would be great for me to understand,

Thank you
That schematic has pots and CV inputs that add to each other, there is no attenuation control of the signal. That would add some confusion as to how it works!
Kampfzwerg
I'd learn about summing amplifiers first. Then the rest should fall into place.
pfzzz
Thanks This is fun!
SOFTWIRE
To do this you put your voltage source for the potentiometer on the switching node of the input jack. When no cable is inserted the voltage source(+5v or whatever) is supplied to the pot. And when a cable is present the 5v source will be disconnected from the pot. I would place a small resistor between the voltage source and the switching jack though.
pfzzz
assuming that the pot value is -4v and CV in is 4v, that would be 0 input assuming that there is a sum, this is kinda confusing. Is my understanding correct ?

I guess I'm trying to reach a different outcome, which is using a pot as attenuator when CV in is active, and pot as a source when not connected.

having the switching jack from +5v, and CV in to the pot input would work correct ?
pfzzz
SOFTWIRE wrote:
To do this you put your voltage source for the potentiometer on the switching node of the input jack. When no cable is inserted the voltage source(+5v or whatever) is supplied to the pot. And when a cable is present the 5v source will be disconnected from the pot. I would place a small resistor between the voltage source and the switching jack though.


Got it, thanks
nigel
pfzzz wrote:
I guess I'm trying to reach a different outcome, which is using a pot as attenuator when CV in is active, and pot as a source when not connected.

It's probably worth pointing out that although this seems like a good way to save some panel space, it's often a bad design. If an input can take either a fixed offset, or a variable amount of CV, then it usually needs both. This may not apply in your case, but think about it carefully.
pfzzz
nigel wrote:
pfzzz wrote:
I guess I'm trying to reach a different outcome, which is using a pot as attenuator when CV in is active, and pot as a source when not connected.

It's probably worth pointing out that although this seems like a good way to save some panel space, it's often a bad design. If an input can take either a fixed offset, or a variable amount of CV, then it usually needs both. This may not apply in your case, but think about it carefully.


Why bad design, or What do you mean by a fixed offset ?

What I am actually trying to do is to have an output value between 0-5v, controlled by either VCC->pot->in, or CV->buffer->pot->in. Did I understand correctly?
nigel
Sorry, I was talking about the design of the controls, not the design of the circuit.
If you switch a pot between a fixed voltage and an input CV, then when you use the CV input, as it is turned down the setting gets closer to zero. This is not always useful.
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