Pot override by CV input

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: Kent, Joe., luketeaford, lisa

Post Reply
pfzzz
Common Wiggler
Posts: 80
Joined: Sun Jun 02, 2019 10:08 am
Location: Germany
Contact:

Pot override by CV input

Post by pfzzz » Fri Nov 29, 2019 3:24 am

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 ... es_v40.pdf

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

Thank you

ixtern
Common Wiggler
Posts: 245
Joined: Mon Jan 22, 2018 4:34 am

Re: Pot override by CV input

Post by ixtern » Fri Nov 29, 2019 4:11 am

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 ... es_v40.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.

User avatar
Mungo
Super Deluxe Wiggler
Posts: 1186
Joined: Fri Jan 04, 2013 8:12 pm

Re: Pot override by CV input

Post by Mungo » Fri Nov 29, 2019 5:16 am

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 ... es_v40.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!

User avatar
Kampfzwerg
Learning to Wiggle
Posts: 35
Joined: Fri Mar 29, 2019 5:23 am
Location: the bellybutton of Europe

Post by Kampfzwerg » Fri Nov 29, 2019 5:55 am

I'd learn about summing amplifiers first. Then the rest should fall into place.
WOMEN AND CATS WILL DO AS THEY PLEASE,
AND MEN AND DOGS SHOULD RELAX AND GET USED TO THE IDEA.

pfzzz
Common Wiggler
Posts: 80
Joined: Sun Jun 02, 2019 10:08 am
Location: Germany
Contact:

Post by pfzzz » Fri Nov 29, 2019 11:29 am

Thanks :cloud:

User avatar
SOFTWIRE
Wiggling with Experience
Posts: 500
Joined: Mon Jul 06, 2009 8:31 pm
Location: Salt Lake City
Contact:

Post by SOFTWIRE » Fri Nov 29, 2019 12:08 pm

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
Common Wiggler
Posts: 80
Joined: Sun Jun 02, 2019 10:08 am
Location: Germany
Contact:

Post by pfzzz » Mon Dec 02, 2019 10:08 am

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
Common Wiggler
Posts: 80
Joined: Sun Jun 02, 2019 10:08 am
Location: Germany
Contact:

Post by pfzzz » Mon Dec 02, 2019 10:18 am

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
Veteran Wiggler
Posts: 743
Joined: Wed Jan 16, 2013 6:49 am
Location: Melbourne, Australia

Post by nigel » Mon Dec 02, 2019 4:36 pm

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
Common Wiggler
Posts: 80
Joined: Sun Jun 02, 2019 10:08 am
Location: Germany
Contact:

Post by pfzzz » Tue Dec 03, 2019 5:58 am

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
Veteran Wiggler
Posts: 743
Joined: Wed Jan 16, 2013 6:49 am
Location: Melbourne, Australia

Post by nigel » Tue Dec 03, 2019 8:32 am

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.

Post Reply

Return to “Music Tech DIY”