Free Project: Make a Cardboard Resistor Calculator

Resistors are identified by a color code that is printed on the body of the resistor.  You can tell what the resistance is by de-coding the colored bands.  I can never remember what each color stands for, so I like to use one of these goodies.

What you will need

  • Color printer
  • White card stock or heavy paper
  • Scissors
  • Hand-held hole punch
  • 3 brass brads (small)

Step 1 – Print out the template

(available here: BoysDad.com_resistor_calculator).  It is best to use some heavy card stock or to have the printout laminated.  If you do laminate it, I have found the best prices are available at teacher supply stores.  You will need to use a color printer, since the whole thing relies on colors.

Step 2 – Cut out Reference Chart (optional)

You don’t need the reference chart to use the calculator, but it is handy to have up above your electronics work bench.

Step 3 – Cut Out Calculator Parts

Be kind of careful,  If it is not nice and straight, the dials won’t line up.

Step 4 – Fold

Again, if you are not careful, the dials won’t line up properly.

Step 5 – Punch

If you put the hole punch on upside down, you will be able to see clearly how to line up the hole with the punch.  Punch all six holes.  It is fine to punch through both sides of the card.

Step 6 – Install the Dials

In this version, all three dials are identical, so there is no need to keep them separate.  Just be sure they are facing so they show through the holes.  I used a pen to poke the holes in the body and the wheels to help the brad go through the very center.  This is a good way to help everything to line up.


The wheels will overlap each other, but they should fit just fine.

Step 7 – Tape the Flaps

The flaps kind of help hold things together  (and make sure your shirt is on right-side-out).

Step 8 – Enjoy

The first two colors on the resistor tell the numerical value of the resistor.  The last color indicates the magnitude of the other two numbers.  For example, if the three colors on a resistor are Red, Black, Black, the value of the resistor would be 20 Ohms.  If it were Red, Black, Green the value would be 2,000,000 Ohms (add 5 zeros behind 20).

This is a simplified version of the one Osgeld posted on Instructables.  Osgeld got the idea from an old Radio Shack product that is no longer being made.   We tried to make our version a little easier to make and use, but it is pretty much the same idea.



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