7. CREATE MOUSEY’S EYES For Mousey’s eyes, we can use the mouse’s own two IR emitters, a.k.a. phototransistors. During normal computer mousing, these shine infrared through the mouse’s perforated encoder wheels, which is then received by photodetectors on the other side.

IR emitters

Like many fundamental devices, these emitters can work as both transmitters and receivers. As receivers, they’re more robust and less specialized than the mouse’s dedicated internal photoreceivers, and this makes them a better choice for Mousey’s eyes to the outside world. On most mice, the emitters are clear plastic boxes with a tiny dome protruding from one face, while the detectors are solid black.

A pair of IR emitters will serve as your robot’s eyes. Note their likely location on the mouse’s PCB.

Find the clear emitters and desolder them from the PCB. You are now the proud owner of a pair of robot eyeballs.

8. GIVE MOUSEY EYESTALKS Our IR emitters only have two stubby little pins coming out. We need to give Mousey some optic nerves − eyestalks that jut from the front of its body. These not only look cool, but also allow you to adjust Mousey’s sensitivity to light by bending the stalks around.

First we need to determine which pin on each emitter is positive and which is negative. Set your digital multimeter to Diode Check mode, and touch the probes to each pin. If the read-out is “OL” (no connection), reverse the probes. When connected correctly, you should get a reading of about 1V, with the red probe indicating the anode (or positive) pin. If your DMM doesn’t have Diode Check, look for a positive voltage of about 0.6V when the red probe is on the anode.

Our finished eyestalks, ready to shed some light on our control circuit.

that hold their shape when you mold them.

Solder the red wire to the cathode (-) pins on the emitters and the black wires to the anode (+) pins. The colors are switched because we're reverse-biasing the diodes; with current flowing in the normal direction, additional electrons excited by light in the diode's junction get lost in the flow, but with current

To create the stalks, cut four 6½" pieces of 22- trickling the opposite way, the difference is more gauge, solid-core hook-up wire. If you have red and noticeable, making the circuit more sensitive. When black, cut two of each color. Solid core is better than the wires are soldered in place, twist them together stranded in this case, because it makes stiffer stalks and strip some of the jacket off of the other ends.