CHAPTER 18 ■ ADDING GEARHEAD MOTORS
Connecting the Diode in the Proper Orientation
You must connect the cathode end of a diode (the end with the band) to the collector (output) of the
transistor. Don’t mistakenly insert the diode in a different direction, or the motor and lights won’t work. If
the diode’s anode were connected to the transistor’s emitter, it would create a high-current path harmful to
the diode, transistor, battery, and even the breadboard.
You must connect the anode end of the diode (the end without the band) to the negative bus. A diode
connected this way won’t normally conduct current.
Connecting the Motor
Use a pair of IC hook jumpers to connect each end of the motor to each end of the diode. The motor is
marked underneath with a plus (+) sign to indicate the positive terminal. Using an alligator jumper or IC
hook jumper, connect the motor’s positive terminal to the cathode of the diode. Connect the other terminal
of the motor to the anode of the diode.
Although there’s no harm in connecting the motor backwards, the motor would run in reverse. In the
final robot, such a mix-up could cause the robot to run backwards or to spin.
Repeating the Setup for the Other Transistor
Connect the second diode and second motor to the other transistor. In this way, one motor and diode should
be attached to Q7 along with the yellow LEDs. And, one motor and diode should be attached to Q8 along
with the green LEDs.
Figure 18-7. Motor and diode added to the brightness comparator circuit on a solderless breadboard