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Potentiometer Questions?

Discussion in 'General Electronics Discussion' started by ikrananka, Oct 25, 2018.

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  1. ikrananka


    Jul 10, 2009
    First off - I'm a complete newbie so apologies if my question appears to be rather stupid.

    I'm trying to put together a small PCB to improve the composite video from an old video game console, the Odyssey 2. I'm basing my PCB on a schematic from here and shown below.


    The issue I have is around the potentiometer connections and I've highlighted the area of my question in the attached schematics. The original schematic shows a connection from one of the ends of the potentiometer looping back to pin 2. What is the purpose of this? I've seen someone else do a PCB based on this design and they did NOT include this connection - see second schematic.


    Why would the loopback be necessary and I guess my ultimate question is which is correct?

    I also have a related question and that is does it matter for the PCB which way round I have the potentiometer, i.e. does it matter if the video output comes from pin 1 or pin 3 of the potentiometer?

    Many thanks for any help.
    Last edited by a moderator: Oct 25, 2018
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The potentiometer is simply used as a variable resistor (also known as rheostat). It will work just the same with or without the connection. The advantage of using the connection between wiper and endpoint is that if the wiper has a bad contact, there will be at least some resistance which may come in handy for some circuits. It is imho not required here.

    Not if the potentiometer is of the linear type.
    Another type of potentiometer has a logarithmic characteristic and is typically used in audio applications, In that case it will matter which way you connect the potentiometer.
    I presume here you will use a linear potentiometer so the orientation is irrelevant. Connect it in a way that operating the potentiometer is intuitive to you.
  3. ikrananka


    Jul 10, 2009
    Many thanks Harald - just the info I needed. Really appreciate your quick response.

    BTW - I will be using a linear potentiometer so I'll orientate the pot whichever way suits me best.
    davenn likes this.
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