Monday, January 21, 2013

Resistors: MacGyver Style

MacGyver Style?

I know there are quite a few international viewers to this blog and I don't know what kind of international penetration MacGyver had but if you don't know him you can read more here. In every episode he would "solve complex problems with everyday materials he finds at hand, along with his ever-present duct tape and Swiss Army knife." Basically, he was an extreme hacker.

DIY Resistors

With that in mind the thought occurred to me today; "What would MacGyver do if he needed a resistor?" Well, he'd make one of course. I did just that and so can you with just a few simple materials. You might have seen the demonstration before where you can create a variable resistor with a pencil and a piece of paper. Basically you color a thick pencil line on your paper and then use your multimeter to measure the resistance between two points along the thick-colored pencil line. The closer you put the probes the lower the resistance. If we're just looking to throw together a fixed resistor in a pinch we can do that too. All we need is:

  • A graphite pencil
  • Some hookup wire
  • Duct tape of course
Now that you have your supplies let's build this thing.
  1. First you'll need to remove some insulation off the ends of your wire. Use your wire strippers if you want but if you want the full MacGyver experience use your teeth.
  2. Rip a piece of duct tape so you're left with a piece about 1cm wide by 4cm long.
  3. Using your pencil, color on the sticky side of the piece of duct tape to create a thick line that will serve as the resistor material. Another way to do this is to color on a surface like paper or wood and then press the tape onto the surface and pull off the graphite. Be careful not to touch the graphite once you've penciled it on because you need every bit of it.
  4. Lay the wires on to the sticky side of the tape with the leads near each other but not touching and centered on the thick penciled line. Remember, the closer the leads are together the smaller the resistance.


  5. Fold the duct tape in half and firmly press it together.


  6. Measure the resistance and marvel at your MacGyver skills.

My Resistor Isn't Working

The most common problem is that you didn't get enough graphite to transfer onto the tape. You need to really lay down as thick a coat as you can. It's tough on the tape surface but doable. Another issue you might encounter is not putting the wire leads close enough together. I put mine about 2 millimeters apart and got a 20K resistor as seen above.

Resistor Quality

Now of course this DIY resistor is not going to have very tight tolerances and it's pretty difficult to get down to lower resistances unless you really step up your manufacturing process. Transferring graphite onto paper and measuring resistance directly on the paper I was able to see a pretty linear measurement of about 1K/mm. That trend held through about 3K and then it got less linear and the resistance started to increase less with distance. A 2cm distance between the leads on paper gave me about 11K. I tried paper, cardboard, and duct tape as substrates and found paper to provide the lowest resistances.

Conclusion

So that's one way to make a resistor. Give it a try and let me know how it turns out. If you make any breakthroughs that make it easier or give you better results I'd love to hear about it.


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