MEAM.Design - MEAM 410/510 - A2: Motors and Memory

1 H-bridge Switch

What type of mechanical switch would you use to create a full H-bridge to drive a motor bidirectionally from a single-sided supply? Draw a wiring diagram showing how you would connect the switch to power, ground, and the motor.

2 Motor Primer

Given a ideal motor (i.e. - no friction) with a nominal voltage of 3 Volts, a stall torque of 5.35 mNm, and a terminal resistance of 2.22 Ω, at what speed will the shaft rotate if subjected to a constant 2.0 mNm load? How much current will the motor draw at this operating point? What will be the electrical power draw at this point? If rated for 2.0 Watts, will this motor be capable of sustained operation under this load?

3 Bi-directional Motor Control

You're designing a control box for a device that needs to drive two motors bi-directionally. You have a quad half-H driver (SN754410), a hex inverter (74HC04), and a bank of four SPST switches with which you can control both motors (use two for each motor, with one controlling whether the motor is ON or OFF, and the other controlling the direction of rotation). Draw a schematic and create a truth table comparing the state of the four switches to the resulting behavior of the motors.

4 Motor Drives

Design three candidate circuits to turn on a motor (12.0V, 5Ω, 800mH) when a low-current microcontroller output (10mA max source/sink current) is switched from low to high (0 to 5V) using each of the following (note - you only need to turn the motor in one direction):

a) discrete TIP31C transistor(s)

b) discrete IRF630 MOSFET(s)

c) an SN754410

Draw a schematic for each case, specify any additional components that you would need, and show any calculations that were necessary to ensure proper functionality.

5 Logical Memory

You have two normally-open (NO) momentary (MOM) SPST pushbuttons, an LTL-4224 red LED, a 74HC02 IC, a 5V supply, and a bunch of 1/4-Watt resistors. Design a circuit such that when the user pushes the first button, the LED turns on, and stays on after release. Then when the user pushes the second button, the LED turn off and remains off until they again press the first button. Include a schematic of your design and show all calculations.