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Thread: Max Potentiometers on 3.3v line

  1. #1
    Junior Member
    Join Date
    Aug 2016
    Posts
    7

    Max Potentiometers on 3.3v line

    Good afternoon,

    I am designing a circuit which includes 17 linear potentiometers - can I connect these to the 3.3v out pin (I am going to use a Teensy 3.5 for this project) or should I add in a seperate 3.3v supply for them? I know the Teensy has a 250mA supply limit but have no idea what each fader will use (I'm assuming very little as it's a voltage divider but not sure).

    Regards,

    Matthew

  2. #2
    Senior Member
    Join Date
    Feb 2015
    Location
    Finland
    Posts
    123
    Let's say you use 10 kOhm linear potentiometers. You connect one end to +3.3V, the wiper to your input, and the other end to GND, to use the potentiometer in the voltage divider configuration. Using U=RI, or rather I=U/R, we know that the current through each potentiometer is 3.3 V / 10000 Ohm = 0.00033 A = 0.33 mA. (This is wasted as heat, at a power of UI = 3.3V 0.00033A = 0.001089 W, or about 1 mW.)

    If you have 17 of those, the current through the potentiometers is 17 0.33 mA = 2.31 mA; and about 17 mW is wasted as heat.

    So, if you use 10k linear potentiometers, which are rather commonly used for this kind of thing, you can quite safely use the 3.3V pin on the Teensy.

    If you use 1k linear potentiometers, the current through each is 3.3 mA, so your 17 pots would consume 56.1 mA total (and generate 185 mW of heat). I'd say this is still okay, but I would not go any lower resistance.

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