10b. Cross a wire from Pin 8 to Pin 11 and another from Pin 6 to Pin 9. These two wires will reverse the motor connections when the relay is engaged.

10c. Plug the capacitor's positive lead into an unused row just left of the relay, and the cathode to the negative power bus. On electrolytic caps, the cathode is usually marked with a stripe or (-) symbol.

10d. Plug in one end of the higher-ohm resistor to connect with the capacitor anode, and jump the other end over the trench to a new node on the other side.

10e. Spread the transistor’s pins and plug it in with the flat side facing the trench, above the relay, such that the center pin (base) connects to the resistor lead, the left pin (emitter) is in an unused node, and the right pin (collector) connects to Pin 16 of the relay.

Our breadboard with control chip, timer, 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.

10f. Plug one hook-up wire into the bottom resistor and capacitor node, somewhere between the two, and a second wire up to the positive power bus. Bend the tips of the wires so they can touch, but keep them separated. These wires will act as the

10g. 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!

11. CONNECT THE MOTORS AND POWER 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.

Bump switch leads

Power + -

Motors -

Finally, connect the 9V battery to the board via a bat- ^{Left motor +}
tery snap or clips, recalling that the battery’s “outie” ^{Right motor +}
snap is its negative pole. Your breadboard should look Finished breadboard circuit with motors and power attached.
like the image at right, and the motors should run. If
so, congratulations! Get yourself a flashlight and start busses into multiple segments; in this case, you
having fun moving the beam around Mousey’s light need to connect the battery to each occupied seg-
sensors, noticing the speed changes. Then touch the ment of the power bus, or else wire them together.
switch wires together, hear the relay click, and see the Use a fresh battery, and probe around with the
motors reverse their direction. 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.

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