# Two potentiometers in series help



## thebestg2002 (Jul 28, 2012)

Hello all. I'm new to the forum and I look forward to hearing from you on a controls issue I need help resolving.

I have a customer who has an electrically controlled cylinder that is used to simply push caulk out of gun. The controller for the stepper motor has a 5V analog input that is used to control the speed with which it is dispensed. The original design included two 10K potentiometers. The wiper of each pot went through a relay contact (one n/o and one n/c contact of the same relay). The relay was controlled by a switch on the front of the main control panel. The intent of this control was to allow speed adjustment from a foot pedal or from a second pot located on the control panel depending on the switch position.

The customer now wants the control to work a little bit differently. He wants the pot on the control panel to set the max speed for each operator so that the foot pedal can be fully depressed. 

Can I simply wire the wiper from the pot on the main control panel to the positive side of the second pot on the foot pedal? Then take the wiper from the foot pedal pot to the analog input.

For example: If the c/p pot was set for an output of 3V for operator #1, then the foot pedal pot would have a total range of 0-3V for that operator. If operator #2 likes it a little slower, then he/she could turn it down to 2V limiting the range of the foot pedal from 0-2V.

What am I missing here? Is there something I need to be concerned about? My circuit theory is a bit rusty. 

Thanks for your help.


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## MDShunk (Jan 7, 2007)

No problem, but the value of the pot on the control panel will need to change. Actually, both pots may need to change.


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## thebestg2002 (Jul 28, 2012)

Hello MDShunk

Could you please elaborate? Like I said my circuit theory is more than a bit rusty.

Thanks


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## MDShunk (Jan 7, 2007)

thebestg2002 said:


> Hello MDShunk
> 
> Could you please elaborate? Like I said my circuit theory is more than a bit rusty.
> 
> Thanks


Sure. I have to step out for about an hour, so unless someone beats me to it, I'll do some calculatus eliminatus and scribble something out.


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## MDShunk (Jan 7, 2007)

I'm thinking of using your existing pots in a novel way as an adjustable voltage divider. Typically, you'd use one pot for that, but you want one to control the limit also, so I draw them both. Indeed, one terminal on each is unused.


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## thebestg2002 (Jul 28, 2012)

This is what I had in mind.


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## Greg (Aug 1, 2007)

Just out of curiosity, since the customer only wants speed control at one location, why not make the foot pedal a basic on/off switch and use one pot on the control panel for speed. I am not understanding the need for two pots or am I missing something in what the customer wants/needs.


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## Splash (Apr 11, 2008)

Greg said:


> Just out of curiosity, since the customer only wants speed control at one location, why not make the foot pedal a basic on/off switch and use one pot on the control panel for speed. I am not understanding the need for two pots or am I missing something in what the customer wants/needs.


Read it a couple times like I had to do. He still wants speed control with the foot pedal but wants to set the max speed the foot pedal can achieve.


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## thebestg2002 (Jul 28, 2012)

You are correct, Splash. I think what I have in mind will work, but I won't be able to test it until next week.


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## Greg (Aug 1, 2007)

Okay, I got it now. See that is what happens when you go to work for the Gov't., you become stupid.


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