CHAPTER 22 ■ SOLDERING AND CONNECTINGPreparing and Attaching the Switch Wires
Like the motors, the switch terminals need to have stranded wires soldered to them and then be covered
with heat-shrink tubing (see Figure 22-21). Unlike the two-pin Molex connector attached to each motor, the
switch ends in a four-pin Molex connector. The four pins are wired as follows: right motor, right transistor,
left transistor, and left motor.
Figure 22-21. DPDT center-off switch (left), heat-shrink tubing (center), and various lengths of wire (right)
To make the wires more identifiable, use different colors. I chose yellow and green for the transistor
outputs, which matches the LED colors. I chose white and red for the motors, since they’re both receiving
positive voltage.
To make the wires fit into the small eyelets in the switch terminals, use thinner wire than was used with
the motors. Instead of #22 AWG, I chose #26 AWG (bigger numbers indicate smaller wire) for the switch.
- Cut four wires total (one each of white, yellow, green, and red) to a length of 15 cm.
- Strip 0.75 cm of plastic insulation from one end of each wire.
- Strip 0.35 cm of plastic insulation from the other end of each wire.
- Cut two more wires (red and white) to a length of about 6 cm.
- Strip 0.75 cm of plastic insulation from both ends of both 6 cm wires.
- Cut one piece of yellow, one piece of green, two pieces of red, and two pieces of
white heat shrink tubing (six pieces total) to a length of 1.5 cm.
Soldering the Line-Following Switch
A DPDT switch has six terminals: Three terminals for the first pole and three terminals for the second
pole. Depending on the position of the switch, the center terminals can be switched to connect to the first
terminals, no terminals, or the third terminals.
- Loop the green wire through the eyelet in a center terminal, twist the wire
together, and solder (see Figure 22-22). This is the same technique used to
connect wires to the motors.