CHAPTER 18 ■ ADDING GEARHEAD MOTORSDetermining the Actual Current (Average Case)
The average current of the motor is going to be somewhere between 31 mA (best case) and 380 mA (worst
case). By connecting the multimeter to the robot and following it around, the load current turned out to
fluctuate between 40 mA and 120 mA. Counting the chips and lights, and assuming only one motor turns at
a time, the robot should last a little under an hour.
Adding Motors to the Brightness Comparator Circuit
The schematic illustrated in Figure 18-5 is a portion of the previously presented brightness comparator
circuit with transistors, with the addition of a diode (D1) and a motor (M1). To reduce visual complexity,
only one branch from the comparator’s two outputs is shown. Imagine that the branch with transistor Q8
(not shown) also has a diode and motor attached.
Figure 18-5. Schematic of motor and Schottky diode added to brightness comparator circuit
Motor M1 has its positive terminal connected to the output of transistor Q7. The motor’s negative
terminal is connected to the negative terminal of the battery. Because the transistor provides power to the
motor, the motor turns on when the transistor turns on.
Introducing the Diode
A diode is very similar to an LED (Light-Emitting Diode) except an ordinary diode isn’t designed to emit
light. However, like an LED, the diode only works in one direction. Also like an LED, the arrow in the diode’s
schematic symbol (see D1 in Figure 18-4) points the direction current is allowed to flow.