The completed touch block is made by mounting the momentary switch in the center of a one-inch piece of c-channel. LED can be secured to case with a spot of glue if needed.
Drill hole in case bottom to allow a press fit for LED. Strip and tin the remainder of the red wire and solder it to the negative (see flat spot) side of the LED and feed the end back through the hole in the case along side of the black wire. Then, strip and tin the wire lead to attach to the current resistor on the positive side of the LED. Solder the resistor to the to the positive side of the LED. Continue pulling the red wire until it is completely free of the case.Ĭut the red wire about 1” from the contact plate. Then grasp the contact with the RED wire using small pliers and gently slide it upward and out of the holder. Push the wires back into the holder to give them some slack.
Open the battery holder and locate the contact plates with the red & black wires attached. Only one hole needs to be drilled to fit the size LED used. Power is provided by 2 AA batteries housed in the holder. On the completed tester, touching the red & black clips together makes the LED light up. Provide spring loaded plunger for the plate.ġ-ea 2” length of stranded hook-up wire (14-18 ga. I used a scrap of brass shim stock that I had on hand.ġ-ea Mini SPST momentary switch (N.O.) Radio Shack #275-1556. Have something suitable on hand, just buy an extra one of these to cannibalize.ġ small piece 1/16” thick conductive stock that you can solder a wire to, such as copper, brass, etc. Spring removed from the holder (left over from a previous project) that I used. I used a scrap of a 96” piece sold at Homeĭepot # 030699-568703 selling for under $11.00.ġ-ea 2-AA Battery Holder (enclosed 3.1v) Radio Shack # 270-408. If you have a 'junk box' cost may be zero.ġ piece of 1/16” aluminum C-Channel 3/4” x 1.5”. Note: you can determine the value of the resistor needed by going to: andĮntering the supply voltage (3.1), forward voltage of the LED (2.5), and desired LED currentī) Touch Block parts Estimated cost: less than $10.00. Estimated cost: $10.00 or less before tax and shipping, if any.ġ-ea 2-AA Battery Holder (enclosed 3.1v) Radio Shack # 270-408ġ-ea 5mm Red LED Radio Shack #2760041 or equivalentġ-ea Current Limiting resistor to match your LED (24ma or less) typically 27 – 56 ohm.
Skip this if you already have a continuity tester that is suitable for use with the touch block. The project is actually two easy projects in one: 1) the touch block, 2) the continuity tester which powers the touch block and provides a LED indicator to show when the tool makes contact with the plate.Ī) Continuity Tester parts.
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