The buttons on most computer mice are separate, semi-attached pieces of plastic. To give Mousey’s eyes a solid foundation, glue the buttons down, wait until dry, then drill small holes in Mousey’s lid to thread the eyestalks through.

Thread about 1¾" of stalk through each hole. On the inside, trim the two red wires so that they just overlap against the underside of the lid. Solder them together. Run the black wires along the inside, to the back, and bend them down where the op-amp is located (don’t solder them yet).

Make the sensitivity booster circuit by cutting a 1" piece of red wire, and soldering one end to the 1k-ohm resistor and the other to the LED’s anode.

Connect the booster by soldering the free end of the resistor to the middle pole of the toggle power switch and the LED cathode to the junction of the two red eyestalk wires.

Mark where the LED sits, gently bend it aside, and drill a hole in the case for it to poke out of (unless it can already come up through the scroll wheel slot). Push the LED through and hold it in place with tape.

We almost got bot! Now install the front whisker and make the final connections between power, the switch, and the control chip. There’s no photo of these final steps, because they happen inside a semi-closed mouse. But you’re such a circuit-hackin’ fool by now that you don’t need us anymore.

Solder the black eyestalk wires to Pins 2 and 3 on the LM386.

Solder the red battery wire to either of the side poles of the toggle switch.

Solder a red wire from the toggle’s center pole to Pin 6 of the IC, or to either Pin 1 or Pin 8 of the relay. Solder another red lead from the unconnected bump switch pin to one of these same locations

Cover all exposed leads and junctions with electrical tape to prevent shorts. Then glue or loosely tape your plastic “whisker” to the bumper switch, so that it clicks on impact.

Finally, snap in the battery, and screw or tape the two mouse halves back together. Then put Mousey on the floor, switch it on, and watch it go!

If all went well, Mousey the Junkbot's behavior will be apparent once you flip its tail. It should zoom away and eventually hone in on the brightest area in the room. It works best if you limit Mousey's surroundings to just one bright source of illumination − one light or sun-soaked window. Below are some other fun experiments to try.

Put Mousey in the hallway and close all doors except one. Make the open room as bright as possible, and see if Mousey eventually scuttles in there. Try orienting Mousey in different starting positions.

Tune Mousey's light sensitivity by bending the eyestalks. Move the stalks farther apart, closer together, and bend in different directions until you get the steering you’re looking for.

Use a flashlight to lure Mousey around. This drives pets insane! But be careful; agitated pets will attack Mousey and try to rip out its little robot heart.