■ Now we’re ready to connect the motors and power and see if it all works. Take the right motor and connect its negative terminal to Pin 5 of the LM386 chip and its positive terminal to Pin 13 on the relay. Take the left motor and connect its negative to Pin 5 of the chip, and positive to Pin 4 on the relay. On many motors, the positive terminal is marked with a dimple or a (+) symbol.

Finally, connect the 9V battery to the board via a bat¬tery snap or clips, recalling that the battery’s “outie» snap is its negative pole. Your breadboard should look like the image at right, and the motors should run. If so. congratulations! Get yourself a flashlight and start having fun moving the beam around Mousey’s light sensors, noticing the speed changes. Then touch the switch wires together, hear the relay click, and see the motors reverse their direction.

If all did not go well, check that everything’s where it should be. with the capacitor, resistors, and transis¬tor in the proper holes and power running in the right direction. Some breadboards split their power

Our breadboard with control chip, tinier, and relay circuits installed.

bump switch when you touch them together. We’re being lazy and assuming that the switch works, but you can hook the wires up to it to make sure.

lOg. Run two wires to connect Pin 1 and Pin 8 on the relay with the top/positive power bus. Connect Pin 9 to the negative bus. Finally, connect the transistor’s left pin (emitter) to the bottom/negative bus. This connects the relay and transistor to power.

That’s it — look over your cool robot brain!

I Left motor + I

— Right motor + 4 -j

Finished breadboard circuit with motors and power attached.

busses into multiple segments: in this case, you need to connect the battery to each occupied seg¬ment of the power bus. or else wire them together. Use a fresh battery, and probe around with the multimeter to make sure that the right amount of power is getting where it should. If the eyes don’t work, check the eyestalk solder joins, and if neces¬sary. swap the eyeballs out for another set from another old mouse. Some definitely work better than others.


■ To prepare the relay for installation, put it in “dead bug mode» (on its back), and solder short lengths of solid-core wire to the bottom four pins (the switch pins) in an X configuration, as shown.

13a. Solder the transistor’s collector (the right pin when you’re looking at the flat side with the pins pointing down) to the top-left coil pin on the relay. Pin 16 on the breadboard. Solder a 4″ piece of black wire (denoting negative) to the transistor’s emitter. This will connect to Pin 4 of the 1C and negative power.

13b. Solder a short red wire connecting the top and bottom pins on the relay’s right side. Pins 1 and 8. Solder a 2″ black (negative) wire onto the bot- tom-left pin. Pin 9. and then a 3″ red wire onto the bottom-right. Pin 8.

13c. Glue the relay into the case, in dead bug mode, and allow it to dry before soldering anything else to it. We glued ours between the motors.

13d. Using red wire, solder the left motor’s positive terminal to the second pin down on the right side (Pin 4 on the breadboard), and solder the right motor’s positive to the opposite pin on the relay.

Pin 13.



With the relay close to the front, we can chain together the timer resistor, capacitor, and bump switch without needing additional wires. As with the relay, we’ll attach components “out of body» first, for easier soldering.

14a. Solder a 4″ black wire to the capacitor’s nega¬tive lead (which should be marked).

14b. Using a multimeter on your 3-pin bump switch, determine which side pin connects with the middle pin when you click, and clip off the other side pin.

14c. Solder the cap’s positive lead to the remaining side pin of the bump switch, and solder one end of the timer resistor to the same pole.

14d. Solder a 2″ red lead to the middle bump switch pin. and then glue the switch into the body, through the hole you cut earlier.

14e. Solder a lead between the transistor’s middle pin and the free end of the timer resistor.



15a. Solder two 2″ black wires to the motors’ negative terminals, then solder the stripped ends of these two wires together side-by-side.

15b. Solder a third. 3″ black wire to these joined ends, then solder it to the control chip’s output pin (Pin 5).



16a. Bend Pins 1 and 8 of the op-amp chip down and solder them together.

16b. Find the black wires from the transistor, the relay, and the capaci¬tor. strip the ends, and solder them all together side-by-side.

16c. Solder the battery snap’s nega¬tive wire to this same junction.

16d. Solder a 1″ black wire to Pin 4 of the op-amp. and the other end to the negative wire junction.

16e. Solder the red wire from the relay to Pin 6 of the chip. Then glue the chip into the mouse case in dead bug mode.

That’s it for Mousey’s bottom half!


17a. 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. and then drill small holes in Mousey’s lid to thread the eyestalks through.

17b. Thread about 1W of stalk through each hole. On the inside, trim the two red wires so that they just overlap against the underside of the lid. then solder them together. Run the black wires back along the inside and bend them down where the op- amp is located (but don’t solder them yet).

17c. Make the sensitivity booster circuit by cutting a 1″ piece of red wire, and soldering one end to the lk- ohm resistor and the other end to the LED’s anode.

17d. Connect the booster by soldering the free end of the resistor to the middle pole of the toggle switch and the LED cathode to the junction of the two red eyestalk wires.

17e. Mark where the LED sits, gently bend it aside.

Sensitivity subcircuit

To Pins 2 and 3 of 1C

Finished insides of mouse top with eyestalk place¬ment. sensitivity booster, and power switch.

and drill a hole in the case for the LED 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 electrical tape.


IIOB 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 in¬side a semi-closed mouse. But you’re such a circuit- hackin’fool by now that you don’t need us anymore.

18a. Solder the black eyestalk wires to Pins 2 and 3 on the LM386.

18b. Solder the red battery wire to either of the side poles of the toggle switch.

18c. Solder a red wire from the toggle’s center pole to Pin 6 of the 1C. or to either Pin 1 or Pin 8 of the re¬lay. Solder another red lead from the unconnected bump switch pin to one of these same locations.

18d. 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.

18e. 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.

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