Nuts and Volts - May 2010

bored or drilled the hole for the laser, it was still off from the sights. I discovered that this was due to the laser manufacturing alignment itself. I decided to add an adjustment.

Laser Electronics

■ FIGURE 6.

positive wire going to the last battery and to access the switch.

9. Drill three #43 holes at 120 degrees 1/8” from the end of the knurled end and tap with a 4-40 tap. Place three 1/8” 4-40 set screws into the tapped holes.

10. Using electrical tape, wrap the last 1/8” to 1/16” of the proximal end of the laser. This will act as a pivot. It can also act as a shim by cutting part of the tape off.

One of the problems I encountered was that if I either

TOOLS NEEDED

Lathe Mill or drill press Knurling tool Soldering pencil Magnifier Curved forceps

#43 Drill 15/64” Drill “L” Drill 1/16” End Mill 4-40 Tap 6-32 Tap 1/4-20 Tap

■ Gunsight Schematic.

The photon emitter uses an inexpensive laser diode (<$10) which is powered by five #10 hearing aid batteries. The detection circuit uses a sub-miniature microphone. When the trigger is pulled, the firing pin causes a click that the microphone picks up. Its output feeds into a PIC12F508 which then pulses the laser for 50 milliseconds. R3 limits the laser’s output. This prevents lock-up. The whole detection system is soldered to a 1” x .225” board (see Figure 4).

Solder the microcontroller to the board noting pin 1, the two 10K resistors, and the .01 capacitor. The microphone is soldered from the top of the board to the square pin with pin 1. Cut the speaker leads short and file or sand so than you can mount the switch to the back of the board. R3 is soldered to the back of the board along with the micro-switch. Using a piece of 1/4” solder braid, fill with solder and bend at a 90 degree angle. Solder this braid to the top and bottom square pads next to the microphone. This will act as the negative contact for the batteries. Carefully cut the wires from the laser to about 3/8” and strip. Solder the red wire from the laser to the square pad next to the chip. Solder the black wire to the round hole. Using a 1” piece of red wire wrap, solder it to the pad next to the solder braid. With the slot and the switch up, thread the wire, board, and the laser from the knurled end. The laser should be flush to the end of the tube. Tighten the Allen screws. The red wire runs along the slot. Trim the red wire to the end of the tube and solder the small brass washer to it (see Figure 5). The switch should be visible.

Use a spring from a ball point pen and cut to a length of 1/4”. Place five batteries into the tube with their negative ends toward the board. Put the washer on the last battery, add the spring, and screw the set screw into the tube. Turn on the switch and tap the tube on the table. The LED should pulse on and off.

The microcontroller goes to sleep and wakes up when it detects the click. However, the two 10K resistors will pull 250 uA. The batteries produce 75 mAh. However, when the laser fires it pulls about 25 mAh for 50 milliseconds.