PWM
Warning
We recommend to use Vicharak 6.1 kernel and latest Ubuntu 24.04 Noble Numbat , in order to support below overlays. Flash Image using this Documentation
sudo apt update
sudo apt reinstall linux-image-6.1.75-axon linux-headers-6.1.75-axon
Introduction
PWM stands for Pulse Width Modulation, a technique used to control the amount of power delivered to a device. PWM generates a digital signal that switches between high (on) and low (off) at a consistent frequency. The key characteristic of PWM is the “duty cycle,” which represents the percentage of time the signal remains high in one cycle.
Axon has total 2 PWMs like,
PWM0andPWM1
Warning
PWM1 can be configured on 2 pins GPIO0_C0 and GPIO1_D3 but with different Mux 0 and 1 accordingly. You can only use any one at once.
Tip
To get more information on Axon GPIO Header.
Understanding Duty Cycle in PWM
A 50% duty cycle means the signal is high for half the time and low for the other half.
A 100% duty cycle means the signal is always high.
A 0% duty cycle means the signal is always low.
Why Use PWM with GPIO?
When a GPIO pin is configured for PWM, it allows you to generate a varying voltage or power level from a simple digital output. This configuration is useful for:
Controlling motors: PWM signals control motor speed by adjusting the duty cycle, which in turn regulates the average power delivered to the motor.
Dimming LEDs: Instead of using resistors or analog circuits, you can dim LEDs by controlling the duty cycle of the PWM signal.
Generating analog signals: Though PWM is a digital signal, when combined with filtering, it can approximate an analog voltage for use in certain types of analog circuits.
How to use GPIO Pins as PWM Protocol ?
Steps to follow for Configuration
Open a terminal window (
Ctrl+Alt+T).Run command
sudo vicharak-configin it.Select
Overlaysoptions in it by pressingenterkey.
┌───────────────────────────────────┤ VICHARAK_CONFIG ├────────────────────────-───────────┐
│ Please select an option below: │
│ │
│ System Maintanince │
│ Hardware │
│ Overlays │
│ Connectivity │
│ Advanced Options │
│ User Settings │
│ Localization │
│ About │
│ │
│ <Ok> <Cancel> │
│ │
└──────────────────────────────────────────────────────────────────────────────────────────┘
You will see Warning Page, click on
yesand selectManage Overlaysoptions.
┌───────────────────────────────────┤ VICHARAK_CONFIG ├────────────────────────────────────┐
│ Configure Device Tree Overlay │
│ │
│ Manage overlays │
│ View overlay info │
│ Install 3rd party overlay │
│ Reset overlays │
│ │
│ │
│ <Ok> <Cancel> │
└──────────────────────────────────────────────────────────────────────────────────────────┘
Select overlays as per your requirement
( PWM0 / PWM1_M0 / PWM1_M1 )by pressingspacebaron keyboard, then selectOk.
┌──────────────────────────────────┤ VICHARAK_CONFIG ├─────────────────────────────────────┐
│ Please select overlays: │
│ │
│ [ ] Enable DP connector-split mode Axon V0.3 │
│ [ ] Enable RasPi Camera V1.3 (OV5647) on CSI0 D0,1 dphy1 Axon V0.3 │
│ [ ] Enable RasPi Camera V1.3 (OV5647) on CSI0 D2,3 dphy2 Axon V0.3 │
│ [ ] Enable RasPi Camera V1.3 (OV5647) on CSI1 D0,1 dphy4 Axon V0.3 │
│ [ ] Enable RasPi Camera V1.3 (OV5647) on CSI1 D2,3 dphy5 Axon V0.3 │
│ [ ] Enable RasPi Camera V1.3 (OV5647) on dphy RX0 Axon V0.3 │
│ [ ] Enable RasPi camera V1.3 (OV5647) on dphy RX1 Axon V0.3 │
│ [ ] Enable UART1 on 30 Pin GPIO Header Axon V0.3 │
│ [ ] Enable UART6 on 30 Pin GPIO Header Axon V0.3 │
│ [ ] Enable UART6 on 30 Pin GPIO Header Axon V0.3 │
│ [ ] Enable PWM0 on 30 Pin GPIO Header Axon V0.3 │
│ [*] Enable PWM1_M0 on 30 Pin GPIO Header Axon V0.3 │
│ [ ] Enable PWM1_M1 on 30 Pin GPIO Header Axon V0.3 │
│ [ ] Enable Waveshare 4inch DSI LCD DPHY TX0 Axon V0.3 │
│ [ ] Enable Waveshare 4inch DSI LCD DPHY TX1 Axon V0.3 │
│ │
│ │
│ │
│ │
│ │
│ <Ok> <Cancel> │
│ │
└──────────────────────────────────────────────────────────────────────────────────────────┘
To return back to terminal, press the
Esckey until you exit from it.In order to enable your configuration, Restart your computer or Run command
sudo rebootin terminal.
Configuring and Controlling PWM’s chip
Befor you dive into below steps, make sure you are in root user.
sudo su
Each PWM chip manages a PWM channel. For example, you want control pwmchip0.
Export a PWM channel:
For export a PWM channel of pwmchip0:
echo 0 > /sys/class/pwm/pwmchip0/exportEnable a PWM channel and set duty_cycle and period:
Set the period (in nanoseconds)
Perioddefines the total time for one cycle of the PWM signal.
echo 2000000 > /sys/class/pwm/pwmchip0/pwm0/periodSet the duty cycle (in nanoseconds)
Duty_cyclecycle specifies how long the signal stays high during one period.
echo 1500000 > /sys/class/pwm/pwmchip0/pwm0/duty_cycleEnable the PWM signal
Enablestarts the PWM output.
echo 1 > /sys/class/pwm/pwmchip0/pwm0/enableDisable a PWM channel:
To stop the PWM output:
echo 0 > /sys/class/pwm/pwmchip0/pwm0/enableUnexport the PWM channel:
When you’re done using the PWM channel, it’s a good practice to unexport it:
echo 0 > /sys/class/pwm/pwmchip0/unexport
Example of using the PWM protocol
This example demonstrates controlling a 3200 RPM DC motor using the PWM (Pulse Width Modulation) protocol.
Setting a higher duty cycle increases the motor’s speed.
Setting a lower duty cycle decreases the motor’s speed.
The motor’s rotation speed depends on the duty cycle — running faster with a higher value and slower with a lower value.
Export a PWM Channel: Prepares the PWM channel for motor control.
Enable and Configure PWM: Sets the period (cycle duration) and duty cycle (signal high time) to control motor speed, then starts the motor.
Disable PWM: Stops the motor by halting the output signal.
Unexport PWM Channel: Releases the PWM channel, resetting it for future use.