Introduction: Custom Resistor Values

Sometimes schematics call for an uncommon resistor value.  Instead of ordering a new resistor online, consider creating a custom resistor by combining multiple resistors together in series.

Resistance adds in series, this means that the total resistance of a series of resistors equals the sum of all the contributing resistors.  The images above show how to wire resistors in series.  When two resistors, R1 and R2, are wired in series, their combined resistance equals R1 + R2.  This principle applies to more than two resistors, three resistors in series, R1 R2 and R3, have a combined resistance of R1 + R2 + R3.

As an example I wired together a 3.3KOhm and a 120KOhm resistor in series on a breadboard in fig 4, the total resistance between the yellow wires is 3,300+120,000 = 123,300Ohms.  In figure 5 I added a 4.7KOhm resistor for a total resistance of 3,300+120,000,+4,700 = 128,000Ohms.


budman56 (author)2014-02-07

could you help me I have a chevy truck gauge cluster that has gauges that I have been told that operate at the value of 12 volt 0 to 90 ohms resistors, I tried to make a device to test the gage but couldn't figure it out here is what I did I used 10k ohm 1/4 watt resistors (see photo) with a dip switch thinking I could add resistors through the operation cycle of the gauge to test the gauge to see if they work, but all I managed to do it to move the needle little bit. so I did some thing wrong. could you tell me how to correct this to make it work?

2014-02-07 22.13.01-700.jpg2014-02-07 22.13.07-700.jpg2014-02-07 22.13.16-700.jpg
russ_hensel (author)2012-06-26

Good but you could ( should ) go a bit farther, using parallel circuits as well give many more options. Additionally you might discuss the impact on power rating of the resulting resistor.

About This Instructable




Bio: I'm a grad student at the Center for Bits and Atoms at MIT Media Lab. Before that I worked at Instructables, writing code for ... More »
More by amandaghassaei:OTCA Metapixel - Conway's Game of Life"9 Degrees of Freedom" IMUTwitter Controlled Pet Feeder
Add instructable to: