Pulse Width Modulation (PWM)

Work in progress

Todo

Add further testing steps, results, and images..

What is it

PWM or Pulse Width Modulation, is a technique used to control the amount of power delivered to an electronic device by breaking up the power signal into discrete ON and OFF periods. The amount of time the signal spends ON during each cycle determines the output power level (brightness of the LED).

How do we do it

To configure HAT pin8 as PWM pin using beagle-pin-mux execute the command below,

sudo beagle-pin-mux --pin hat-08 --mode pwm

Let’s create a script called fade.sh that cycles through LED brightness on HAT pin8 by changing PWM duty cycle.

touch fade.sh

Now open the file with nano editor,

nano fade.sh

In the editor copy paste the script content below,

#!/bin/bash

PWMPIN="/sys/devices/platform/bus@f0000/23000000.pwm/pwm/pwmchip3/pwm1"


echo 1000 > $PWMPIN/period
echo 0 > $PWMPIN/duty_cycle
echo 0 > $PWMPIN/enable
sleep 1

for i in {1..500};
do
        echo $i > $PWMPIN/duty_cycle
        echo 1 > $PWMPIN/enable
        echo $i
        sleep 0.0005
done

for i in {500..1};
do
    echo $i > $PWMPIN/duty_cycle
    echo 1 > $PWMPIN/enable
    echo $i
    sleep 0.0005
done

• Close the editor by pressing Ctrl + O followed by Enter to save the file and then press to Ctrl + X exit

• Now execute the fade.sh script by typing:

bash fade.sh

Fig. 103 LED PWM fade demo

• You can exit the fade.sh program by pressing Ctrl + C on your keyboard.

Todo

Add section about driving Servo Motors at 50KHz

Troubleshooting

Todo

Fill out empty section

Going Further

Todo

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