Circuit Bending Tip #1

If you need to change a potentiometer’s value to work with your project, you can use some simple math to alter an existing potentiometer’s maximum and minimum range. This is something I recently learned after I realized that a 5k potentiometer’s travel was too wide, and I wanted to reduce my potentiometer’s value to between 3k-5k Ohms.

This page has some good information about altering a potentiometer’s value, but I am going to simplify it a little bit.
http://www.allaboutcircuits.com/vol_6/chpt_3/9.html

Basically when you wire up a potentiometer as a rheostat (a variable resistor: a.k.a. the wiper/ center lug and only one other lug) you can change the value by adding a resistor either in series or parallel.

Example 1: If you have a 5k pot, which in theory has a range of 0-5k which you want to have a range of 2-7k, you simply put a 2k resistor in series with the circuit. It can be either attached to the wiper or the other lug. Adding resistors in series adds resistance to the circuit.

Example 2: If you have a 5k pot which you want to change the range to 0-2.5k, put a 5k resistor from lug 1 to lug 3 (the two outside lugs. Adding resistors in parallel subtracts resistance to the circuit.

Example 3: A little from both examples above. If you have a 5k pot and want the span to be between 2k-3k, put a 2k resistor in series (to limit the minimum range to 2k) and place a 7.5k resistor in parallel (between lug 1 and 3, in order to reduce the maximum value to 3k).

There are some nice calculators online for checking the value of resistors in parallel and even in series (although this is as simple as adding the values together).

The potentiometer will always be limited in its maximum span of resistance (in this case 5k), but you can see that next time you order some pots, you can order some more moderate values, and just alter them as need be.

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