CHAPTER 22 ■ SOLDERING AND CONNECTINGGot it? You have two red wires, one long and one short, connecting to the same terminal.- Slide both pieces of red heat-shrink tubing over the pair of red wires.
- Loop, twist, and solder the other end of the 6 cm red wire to the terminal on the
diagonal across the switch.
If one neglects to slide the heat-shrink tubing onto the red wires in step 10, the tubing can’t be added
after step 11 because both ends of the short wire will be soldered to the switch.
Figure 22-23 shows the state of the switch as of completing step 11. The yellow and green wires are
soldered to the center terminals. Two red wires are soldered to the lower right terminal of the switch and are
covered by a piece of heat-shrink tubing. The other end of the shorter red wire is soldered to the terminal
diagonally opposite it, and covered in heat-shrink tubing.
Reasoning Behind the Diagonal Cross Over
Let’s say the 15 cm red wire is connected to the left motor. It’s very important that the red wire leading to the
left motor is connected to opposite terminals on each pole (the diagonal crossover).
Here’s why: Electricity flows into the green wire from the left transistor. When the switch is toggled in
one direction, the green and red wires are electrically connected and power from the left transistor flows
into the left motor. When the switch is toggled in the other direction, the yellow and red wires are electrically
connected, and power from the right transistor flows into the left motor.
If the two red wires were connected to each terminal on the same pole, then the left motor would always
be connected to the left transistor no matter whether the switch were toggled left or right.
If the two red wires were connected to each terminal on the same side of the switch, then the left motor
would be connected or disconnected to both left and right transistors at the same time.
The crossover forces each motor to be connected to only one transistor at a time and the opposite
transistor when the switch is flipped. If none of this makes sense, just trust me and follow the directions.
Finishing Soldering the Line-Following Switch
Follow the same steps with the white wire and the two remaining terminals. That is:
- Loop one end of the 6 cm white wire and one end of the 15 cm white wire
together to the same terminal. You can pick any of the remaining terminals.
I arbitrarily chose the upper right terminal as it appears in Figure 22-23. Twist
together and solder. - Slide both pieces of white heat-shrink tubing over the pair of white wires now
soldered to the switch. - Loop, twist, and solder the other end of the 6 cm white wire to the terminal on
the diagonal across the switch.
All six terminals on the switch should now be wired (see Figure 22-24).