This question requires a bit of background.

I am building a resistor colour-band machine out of an egg carton. The idea is - you are making a project. You are unsure of a precise resistance value you need, so you use a pot. Once you have the setting right, you take the pot, plug it into this machine and it gives you the 5-band colour code for the resistor you need.

The trouble is how to display the colours in the egg-carton cups. I can come up with a few ideas - all flawed:

  • RGB LEDs - but how do you display black and brown?
  • LCD - but where do you get a 2X2cm LCD?
  • Color wheel driven by servo/stepper - but how do you make it fit?

Can you think of any ideas that will work?

  • \$\begingroup\$ You should see how small they can make motors these days... \$\endgroup\$ Commented Dec 14, 2013 at 3:43
  • \$\begingroup\$ @ignacio-vazquez-abrams If you have an example of a small enough motor, why don't you post it? \$\endgroup\$
    – felixphew
    Commented Dec 14, 2013 at 3:47
  • 1
    \$\begingroup\$ precisionmicrodrives.com/dc-geared-motors/dc-gear-motor-ranges/… \$\endgroup\$ Commented Dec 14, 2013 at 4:14
  • \$\begingroup\$ A DC motor seems a bit imprecise - I doubt it could rotate in 36˚ increments. Still, good to know. \$\endgroup\$
    – felixphew
    Commented Dec 14, 2013 at 4:20
  • \$\begingroup\$ Strap an encoder wheel to it. \$\endgroup\$ Commented Dec 14, 2013 at 4:20

1 Answer 1


Why don't you draw the colors on a piece of cardboard or similar material and use the LEDs to indicate which color is needed. You only need to show the first 3 bands since they are for the resistor value, the others are for tolerance and reliability. Thus you would probably need a total of 30 leds, 10 for each of the first 3 bands. But the LEDs could be cheap red ones since they are only being used as indicators. If you want them to occupy a small area, place them in a circular pattern.

  • \$\begingroup\$ That's a good idea, but possibly not small enough. Nice concept though! \$\endgroup\$
    – felixphew
    Commented Dec 14, 2013 at 3:55
  • \$\begingroup\$ EDIT: I tried it, and it fits (just). Still seems a bit squashy, but a clever solution, so I ^1 'd it \$\endgroup\$
    – felixphew
    Commented Dec 14, 2013 at 4:18
  • \$\begingroup\$ I like your solution, but I would like some other ideas. Could you possibly ask anyone else to take a look at the question? \$\endgroup\$
    – felixphew
    Commented Dec 29, 2013 at 4:54

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