TEACHER GOALS

IMPORTANT - Nothing in this lesson should ever get hot - not batteries, not the voltage regulator, not the H-bridge integrated circuit, and not the motors.

Up to this lesson heat hasn't been a problem as all power has been provided by the student computer. With this lesson, however, students build and use a 9 volt battery pack, capable of delivering power and possessing no fuse or other protection.

A good class practice is to have students leave one of their AA cells out of the battery pack except when powering a device or experiment.

In this lesson students are introduced to three new devices - the H-bridge integrated circuit, the analog voltage regulator, and the DC motor. You need your students to come away with the following:

  • Understand how to wire and use the H-bridge integrated circuit
    • The pin numbering and orientation
    • Providing 5 volts to enable the switching logic
    • Providing 6 volts from the voltage regulator to drive the motors
    • The relationship of the motor control pins and the action of the motor
  • Understand how to wire and use the six-volt voltage regulator
    • That voltage regulators come in many different voltages
    • The motors used in this lesson are designed for six volts
  • Understand that DC motors generate a lot of electrical noise and,
    • that noise can interfere with communicating with the robot
    • that steps can be taken to minimize electrical noise
  • Know how to wire a DC motor in such a way that the motor solder terminals are protected from vibration, and generated noise is minimized

COMMON STUDENT MISTAKES

  • Allowing the red wire to touch the black wire in the battery pack connector. This will result in the batteries getting hot. If not attended to, the batteries will eventually generate enough heat to melt the battery holder. Check the wiring of the power plug carefully before allowing students to insert AA cells.
  • Wiring, of course. The lesson contains a wiring diagram but students tend to forget a wire here and there.
  • Placing the voltage regulator along one of the colored stripes - either red or blue. The voltage regulator must be in the white area of the breadboard.
  • Shorting (connecting) the output of the voltage regulator to ground. This will cause the voltage regulator to become very hot, hot enough to raise a blister if touched.
  • Poor solder connections on the motor. Students will sometimes think of solder as something like glue and attempt to daub it on.

HOW TO WIRE A DC MOTOR