Build Your Own Continuity Tester

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The Prologue… (Mysterious, eh?)

God… how to start, how to start… I guess the best place is at the end. “And there it is! Completely finished and working!” No? That’s not right you say? OK, once again, from the top.

What You’ll Need:

  • One Mouse (I used an old serial port mouse)
  • One LED
  • Two AA batteries (or other convenient 3 volt power source)
  • One Two-AA Battery Box
  • About 4′ of wire
  • One Large Paper clip
  • Dremel Tool with drill bit
  • Hot Glue Gun
  • Soldering iron
  • Pliers
  • Phillips and Flathead Screwdrivers

Step One – The Case


Remove all screws from the bottom of your mouse and pull apart the top from the bottom. You won’t need anything other then the outer shell of the mouse, so remove any screws holding the circuit boards to the bottom and set them aside. If you decide to paint your circuit tester, it would be a good idea to remove the button pad beforehand. Most just snap into place, you should be able to pop it out.

Once you have removed all the inside components, flip the top half of the mouse case upside down and mark out the position where you want your LED indicator to be. Drill out a hole slightly smaller than the LED indicator with your dremel tool (or drill whichever you prefer). Your prep-work for the case is done, unless you decide to mod it further.

Step Two – The Wiring


If you couldn’t find wire, one alterative would be to strip the wire you need from the mouse cord you removed earlier.

Trim two pieces of wire, each 1′ 6″ long. These will be your connecting leads for testing a circuit. Solder your positive connecting lead to the positive connection of your battery box. At the other end of your positive connecting lead, solder a small piece of metal from the large paper clip. This is the positive end probe.

Repeat the same process for the negative connecting lead, but do not connect it to the battery box; instead, connect the negative connecting lead to the positive end of your LED indicator. From the negative end of your indicator, solder a piece of wire to the negative connection of your battery box.

Your wiring should now be complete. To test, put in your AA batteries and touch the two ends of your probes together. The indicator should light up.

Step Three – Fitting It All In


Find the best position for your battery box to be in the bottom of your mouse case. I found that the center left worked well for me. Once you’ve decided on a position, push your LED indicator through the hole you drilled, and run your connecting probe wiring through the front of the mouse and shut the case.

If everything fits snugly, open the case again and hot glue your battery box and LED indicator into place. Shut your case again and put in the bottom screws. “And there it is! Completely finished and working!”


This guide was written from the inspiration of not having a continuity tester while helping Elif with wiring in his Project Phoenix case. We ended up using a 9-volt battery and a 12-volt fan he had on hand, but it was a pain to check for connections and breaks. Hope this helps others, and until the next time I do something random, keep on modding.

Johnathan McKnight aka Akoi Meexx


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