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    Lab 3 (2013)

    Digital Outputs,

    a

    Pulse-width modulation, and

    a

    High-Current Outputs

     

     

     

    Jump To
    1. Objectives
    2. Pre-Lab
    3. Additional Info
    4. Lab
    5. Milestone

     

     

     

    Objectives

    • To use the TINAH to operate DC motors and hobby R/C (radio-control) servo motors.
    • To generate digital and PWM output signals, controlled by the TINAH Board, capable of driving high current resistive and inductive devices such as heaters, coils, and motors. The circuits developed here will be required to operate your drive system.

     

     

    Pre-Lab

    1. Read about the TINAH Board’s motor driver circuitry from the class notes.  Plot the expected waveform from the TINAH motor output pins for an 80% duty cycle signal and for a -80% duty cycle (80% at reversed polarity)
    2. Familiarize yourself with the IRF5305 and HUF75321, the two MOSFET devices used in the course.   Downloads section ».
    3. Review the datasheets for the 3904 and 3906 BJTs.   Downloads section ».

     

     

    Additional Info

    1. You can learn about RC servo motors, and the type of signals which are used to power them.  Servo Motor Intro (Seattle Robotics)  »

     

    Lab


    1.)  Directly drive a DC motor with the TINAH.

    Write a program to drive one of your team’s motors directly using the TINAH  Board motor outputs.

      1. Make your program read in the value of the knob and use that value as the speed value (eg.  Set knob=512 as speed  = 0; knob = 0 is speed= -1023, knob=1023 is speed=1023…).
      2. Note the amount of torque which you get when your motor is going at full-speed in either direction.  The current is limited by the 9V regulators on-board the TINAH which are used to power the on-board h-bridge chips (for the detailed schematic of the board, check the schematics online .  TINAH schematics >> ).

     

    2.)  Drive an RC servo motor with the TINAH.

    Attempt to get one of the RC Servo Motor outputs to operate with the TINAH Board.  Code and pinout information can be found here:

     

    3.) View the  high-impedance ouptuts of the TINAH motor outputs.

    Remove the motor and connect the two connections from the TINAH motor output to ground with a 10K resistor.  Observe the voltage waveforms at each motor output with respect to ground.  Remove the 10K resistor and observe the change in the voltage waveforms.  Sketch out the change in the resulting waveform; this is a result of the high-impedance state of the outputs when the motors have no current being driven through them.

    Pinout information for the DC motors and the indicators can be found here:    Hardware description of DC Motor Outputs >>

     

    4.) Make an external H-bridge circuit.

    The TINAH Board motor outputs are not capable of driving the high-torque motors provided in your kit at full current.  In order to generate an appropriate signal, the signals derived from the TINAH Board motor outputs can be manipulated and used for motor control.  Today, you will use 15V from the benchtop power supplies, but in the future, you should be able to use the 12V batteries with the same circuit.

      • In addition to the circuit shown below, you will also need to add the comparator circuit as discussed in the lecture.  The comparator circuit is required to interface the TINAH motor output signals (analyzed in the previous step)  to the H-bridge circuit in the diagram.
      • Watch the MOSFET temperature as you apply power to the circuit.  If it gets hot, shut power off, remove the MOSFETs, and check the voltages where the gates of the MOSFETS would be located – you should see them transition from 0 to 15V as required.
      • Make sure you use the TINAH Board 5V supply as the source of the comparator threshold voltage.

     

     

    Milestone

    Demonstrate motor control with your H-Bridge driven by the TINAH Board

    Complete and submit the  Class Survey given out at the start of the lab.

     

     

     

     

     

     

    HB-1 nd HB-2 refer to connection points to signals coming from the TINAH Board. As you will find, the TINAH Board motor outputs are not appropriate for plugging directly into this circuit. You will need to design a comparator circuit to drive the inputs HB-1 and 2 at the correct voltages.

    HB-1 HB-2
    STOP (BRAKE) lo lo
    FORWARD hi lo
    REVERSE lo hi
    NOT ALLOWED hi hi

     

    Max Current Max Voltage Rds(on)
    N-channel Enhancement
    MTP 3055 (old MOSFETS for course) 12 A 60 V 0.15 ohm
    IRFZ14 (old MOSFETS for course) 10 A 60 V 0.20 ohm
    HUF 75321 35 A 55 V 0.028 ohm
    P-Channel Enhancement
    MTP 2955 (old MOSFETS for course) -12 A -60 V 0.23 ohm
    IRF 9Z14 (old MOSFETS for course) -6.7 A -60 V 0.50 ohm
    IRF 5305 -31 A -55 V 0.06 ohm