Resistor Color Wheel Tool

I made this paper reference tool to help us find the right resistor without having to look it up online. It's portable, colorful, and easy to make.

Tools required:

(printer and glue stick) or (protractor and compass)

pencil with eraser

ball point pen

stapler

hole punch

scissors

ruler

crayons: black, white, grey, purple, blue, green, yellow, orange, red, brown

Materials required:

white cardstock paper or standard printer paper and thin cardboard from the recycling bin

brad fastener or a paperclip with a small bead

If using a printer: Print one page of the Resistor_Color_Wheel.pdf on cardstock. If you don't have cardstock, print on plain paper and glue the printout to thin cardboard from the recycling bin. We used a cereal box. :)

If using a protractor and compass:

Draw circles and mark the centers. The exact sizes can vary. Here are the dimensions of a set I made.

• large circle (14.5 cm diam)
• middle circle (10 cm diam)
• small circle (5 cm diam)

In all 3 circles, use a compass to draw ten equal segments, 36 degrees each.

In the middle and large circles, draw two more circles around 1.5 cm and 3 cm from the edge. Color the outermost ring segments clockwise by color order: black, white, grey, purple, blue, green, yellow, orange, red, brown.

In the small circle, draw one circle around 1.5 cm from the edge. Color the center segments clockwise by the same color order.

In the large circle, write the multiplier in the second ring and fill the outermost ring segments with the corresponding color. Do this in clockwise order.

x 1 ........... black

N/A ........... white

x 100M ...... grey

x 10M ........ purple

x 1M .......... blue

x 100K ........green

x 10K ..........yellow

x 1K ............orange

x 100 ...........red

x 10 .............brown

In the middle circle, write the number in the second ring and fill the outermost ring segments with the corresponding color. Do this in clockwise order.

0 ........... black
9 ............ white

8 ............ grey

7 ............ purple

6 ............ blue

5 ............ green

4 ............ yellow

3 ............ orange

2 ............ red

1 .............brown

In the small circle, color the center segments clockwise and write the number in the outer ring. Use the same numbers and corresponding colors as the middle circle.

Cut out all three disks and poke a hole in the center with a ball point pen. Wiggle around the hole until it is wide enough for a brad fastener to turn. Stack the disks on the bard fastener with the smaller disks on top. The color bands and blank number areas should be visible on each disk. Dismantle the assembly and use a hole punch to create semi circle holes along the circumferences in between colors. Later you will use these divets to spin disks with your fingers.

Cut from cardstock or thin cardboard a square (15 cm x 15 cm) and a rectangle (15 cm x 6 cm). Find the center of the rectangle and square by drawing two straight pencil lines from the corners. At the intersection of the straight lines, poke holes and re-stack all the parts on the brad fastener with the square on the bottom and the rectangle on top. Erase the diagonal lines.

On the rectangle, cut a window on the right to show the color bands and numbers and cut a small area on the center bottom so you can turn the smallest circle. If everything lines up and moves ok, staple the rectangle to the edges of the square and bend the ends of the brad fastener flat.

Write these variable names in pencil above the window and indicate with arrows: "First Color Band","First #", "Second Color Band", "Second #", "Multiplier", "Third Color Band". Once happy with the spacing, trace over with pen and erase pencil marks.

Label your new paper tool with your name and "Resistor Color Wheel". Decorate it how you like and write down useful information, such as:

K = x 1,000

M = x 1,000,000

Fourth band gold = 5% tolerance

Fourth band silver = 10% tolerance

No fourth band = 20% tolerance

V = I x R

I = V / R

R = V / I

Solving for the resistor value

Oh no! You've found a random resistor, and you don't know it's value. The same thing happens to me all the time. Here's how to figure out the resistance value.

• Turn the disks on your your Resistor Color Wheel so the same colors of the random resistor show in your viewing window.
• Write down the corresponding numbers and multiplier. Then do the math.

Let's test with my random resistor, which has these color bands: brown, green, orange, and gold. When I turn the disks, I get 1 for the first number, 5 for the second number, and x1K for the multiplier. My random resistor is 15K ohms. The gold band means the exact resistance could be + or - 5% of 15,000 ohms. Since 5% of 15,000 is 750, my resistor will fall between 14,250 and 15,750 ohms.

When Jack and I test the resistor with a multimeter, we got 14.94 K ohms, which is well within the 5% tolerance.

Solving for the color bands

A more likely scenario is that a circuit calls for a specific resistor value, such as 1K ohm, and you don't know the corresponding color bands. Turn the disks on your Resistor Color Wheel to match the numbers. In the case of a 1K resistor, the first number is 1 and the second number is 0. Now the multiplier is whatever number you need to multiply 10 by to get 1K or 1,000.

10 x (multiplier ) = 1,000

multiplier = 1,000 / 10

multiplier = 100

Turn the large disk until you see x 100. The three color bands showing in the viewing window are brown, black and red.