DIY Resistor Decade Box

This is a simple yet effective resistor decade box. The resistors are connected in parallel with the SPDT/SPST switches. The resistance is the sum of all switches opened(NOT CLOSED!).

When resistors are in series the resistances add up.


And when they are in parallel the total resistance decreases:


Rt is the total resistance in all equations can have an unlimited amount of resistors.

We are going to set them up in a 4-bit binary digit value form where each switch has a resistance of $$Rn=2^{n}$$

Let’s say when you close the switch, the resistance is 0.1 ohm. So let’s say we have a 4 switch box. There are 10,20,40 and 80 ohms used. Let’s close 40 and 80.


Rout=30.19962578 which should be 30 ohms we are close enough

Published by Justin Roeder

I am an electronics engineer and computer programmer that has autism. I learned by myself

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