Use the BeagleBone Black PWM to Capture PWM Measurements

This example shows how to use the BeagleBone Black PWM to generate a square wave of given frequency and duty cycle.

The BeagleBone Black board has eight pulse-width modulation (PWM) output pins. Each PWM pin outputs a square waveform with variable frequency and duty cycle.

In addition to your BeagleBone Black board and USB cable, you must have the following equipment:

  • LED

  • 1 kΩ resistor

  • Breadboard and jumper cables

You will configure a GPIO pin (P9_14) as a PWM pin (PWM1A).

  1. Configure the BeagleBone Black hardware.

    • Using a white cable, connect P9_14 (PWM1A) to the 1 kΩ resistor.

    • Using a white cable, connect the 1 kΩ resistor to the LED input.

    • Using a black cable, connect the LED output to P9_01 (DGND).

  2. Start MATLAB®.

  3. Connect the BeagleBone Black board to a host computer USB port and wait about 30 seconds for the board to start.

  4. Connect the BeagleBone Black driver interface to the board.

    bbb = beaglebone
    bbb = 
    
      beaglebone with properties:
    
               DeviceAddress: '192.168.7.2'
                   BoardName: 'BeagleBone Black Rev 00C0'
               AvailableLEDs: {'USR0'  'USR1'  'USR2'  'USR3'}
        AvailableDigitalPins: {1x29 cell}
         AvailableAnalogPins: {'AIN0'  'AIN1'  'AIN2'  'AIN3'  'AIN4'  'AIN5'  'AIN6'}
            AvailablePWMPins: {}
        AvailableSPIChannels: {}
           AvailableI2CBuses: {'i2c-1'}
        AvailableSerialPorts: {}
            AvailableWebcams: {} 
  5. Enable pin P9_14 as a PWM pin.

    enablePWM(bbb, 'P4_14')
    bbb.AvailablePWMPins
    ans = 
    
        'P9_14'
  6. Set the frequency to 1000 Hz and the voltage to 1.5 V.

    writePWMFrequency(bbb,'P9_21',1000);
    writePWMVoltage(bbb,'P9_21',1.5);
  7. Loop the duty cycle from 0.0 to 1.0 and back again, pausing between increments. Observe the resulting behavior.

    for dc = 0.0 : 0.1 : 1.0
         writePWMDutyCycle(bbb,'P9_21',dc);
         pause(0.2)
    end
    
    for dc = 1.0 : -0.1  :0.0
         writePWMDutyCycle(bbb,'P9_21',dc);
         pause(0.2)
    end

When you are finished using the PWM, restart the hardware to make additional GPIO pins available.