CHAPTER 23 ■ THE MOTHERBOARD
- Repeat steps 18 and 19 for the other end of the wire.
- Slowly, but surely, make your way through each circuit module and solder every
component. Take breaks as needed.
Soldering the Cadmium-Sulfide Photoresistors
Before soldering the photoresistors, it’s beneficial to paint their backs with black paint. The thick, dark paint
prevents direct light from the headlights from leaking from behind and affecting the sensor readings.
Testors Flat Black Enamel #1149 works well (see left side of Figure 23-15). Alternatively, instead of using
black paint with a paintbrush, try a black paint marker. They're easier to guide, which reduces the chances
of accidental brush strokes on the face of the sensor. You can find paint markers at local hardware stores or
McMaster-Carr (part #16625T27, 4 mm black paint marker, $4.00).
Figure 23-15. Black paint (left and bottom) and photocells raised 12 mm from circuit board surface (top right)
When installed in the robot’s body, the circuit board is about 20 mm above the floor, so the
photoresistor and headlight LED leads need to be trimmed short. After soldering, their tips should be about
12 mm from the circuit board surface (see top-right side of Figure 23-15). At the very least, try to keep all of
the photoresistors at the same level.
Trimming Leads with Wire Snips
After everything is soldered, use a pair of wire cutters to trim the excess leads from the board. Long leads are
likely to catch or tangle, and can accidentally touch other long leads, which causes circuit failure. Be sure to
wear safety goggles during lead trimming!