Arduino Forum

General Category => General Discussion => Topic started by: TobiasRipper on Apr 09, 2014, 06:02 am

Title: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: TobiasRipper on Apr 09, 2014, 06:02 am
Simple idea.

Potentiometer from Arduino is hooked up to 5+v and Ground which passes 5 volt and 40ma/h which means top resistance of this connection would be a125 ohm... Then I use an analog input pin to read output voltage of the potentiometer  from 0v - 5v and depending on voltage ranges, make arduino do different things.

my question is: If I use a basic linear 10% tolerance potentiometer but one that is 125k ohm 2 watt, will it damage my circuit? I mean its kinda like using a tank to pry open a jar of pickles...

PS: like this: http://www.ebay.ca/itm/5-x-10K-B10K-OHM-Linear-Taper-Rotary-Potentiometers-/250611909638?pt=LH_DefaultDomain_0&hash=item3a59a24406&_uhb=1
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: CrossRoads on Apr 09, 2014, 06:11 am
125K pot is fine. 10K would be more typical.
http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/linear.html
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: TobiasRipper on Apr 09, 2014, 06:14 am
Oh ok so the the circuitry on the arduino pro mini won't fry if the potentiometer is all the way up right?
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: CrossRoads on Apr 09, 2014, 06:26 am
One outer leg to +5, one outer leg to Gnd, middle wiper leg to Analog pin. That's pretty standard and won't damage anything.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: TobiasRipper on Apr 09, 2014, 06:29 am
Ah thank you very much, and sorry for a primitive question.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: CrossRoads on Apr 09, 2014, 06:30 am
No problem.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: TobiasRipper on Apr 09, 2014, 06:33 am
Oh the only thing I am still wondering... some website have a clear indication for the % of the tolerance of their potentiometers. I am looking for quite high precision since the voltage is going to be converted to a variable and then used. I was looking at 10% tolerance which is pretty suitable however this one:
http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/linear/500-ohm-linear-taper-potentiometer.html

doesn't have (at least one that I can see) a clear indication of its tolerance %.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: CrossRoads on Apr 09, 2014, 06:36 am
If you needed an absolute resistance value, the tolerance would be important.
Using it to dial in a voltage, you just have the ratio of two resistors creating a voltage from 0 to 5V, so tolerance is not important.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: TobiasRipper on Apr 09, 2014, 06:39 am
I would be converting the voltage read from the potentiometer into a variable and then inserting that into an equation which will perform tasks. Like for example generate a pulse width, the rate of which depends on the potentiometer position now that pulse width must be quite precise so I need a potentiometer which can capture slight adjustments.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: CrossRoads on Apr 09, 2014, 06:51 am
Maybe a rotary encoder would be better - capture pulses one at a time, change  your pulse width based on that.
Otherwise, get a higher resolution ADC,  one that can return more than 0 to 1023, with readings that will very a little with no pot change. Another user is seeing his readings wobble 101, 102, 101, 101, 102, with no pot change. Just a function of the ADC you cannot control but must take steps in software to mitigate.
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: Paul__B on Apr 10, 2014, 12:44 pm
Other than minimising cost, there are virtually no justifications for using a potentiometer to feed an analog input on the Arduino.

OK, so a rotary encoder requires two inputs, but most of them (designed as panel controls) incorporate a third switch function as a push-button which enables it to be used as a multi-level menu system to control not just one, but an effectively unlimited number of adjustments.

The rotary encoder allows you much more precise control, has a vastly greater range since it is (unlimited) multi-turn and can be used to implement variable speed selection - turn it faster and it changes the variable much faster, or "press to zoom" in or out as suits the application.  In other words, if you press and release, it selects a menu item, but if you press and turn, it steps more (or if you wish, less) quickly.

Just why would you use a potentiometer and an analog input?
Title: Re: Buff potentiometer on a Arduino Pro Mini? (125k ohm 2w)
Post by: Zapro on Apr 10, 2014, 02:08 pm

40ma/h


current flow is measured in mA (Amps is with big A).

mAh is current over time - when using a pot, you do not use the mAh-rating - it's meant for energy storage - like batteries.

// Per.