12. FREEFORM MOUSEY’S CONTROL CIRCUIT Now that we have a light-hungry robot brain, we need to install it in our mouse body so that it can feed (cue Night of the Living Dead sound effects here). In general, we’ll want to use a lighter wire, such as stranded 22-gauge, to tuck into the case and put less stress on the solder joints.

Before soldering, test fit all the parts inside your case, starting with the battery, motors, and bump switch. Then position the other components around these. The resistor/LED sensitivity-booster circuit will fit against the top half. As you arrange, check that the case still closes, and leave some headroom for the wires. When you’re happy with your arrangement, empty the case and install the battery using two-way tape, Velcro tape, or poster putty. That way, you can replace it when Mousey gets that run-down feeling.

13. INSTALL THE RELAY 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 IC 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.

To timer resistor

To right motor + To left motor +

To Pin 6 on IC (power +)

To Pin 4 on IC (power -)

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.

14. CONNECT THE SWITCH COMPONENTS 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.

Bump switch

-+

To Pin 4 on IC (power -)

To Pin 1 on relay (power +)

14a. Solder a 4" black wire to the capacitor’s negative lead (which should be marked).

To timer transistor

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.