Your board has pwmio support, which means you can PWM LEDs, control servos, beep piezos, and manage "pulse train" type devices like DHT22 and Infrared.
Nearly every pin has PWM support! For example, all ATSAMD21 board have an A0 pin which is 'true' analog out and does not have PWM support.
PWM with Fixed Frequency
This example will show you how to use PWM to fade the little red LED on your board.
The following illustrates how to connect an external LED to a QT Py M0.
In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory CircuitPython_Essentials/CircuitPython_PWM/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY drive should now look similar to the following image:
# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""CircuitPython Essentials: PWM with Fixed Frequency example."""
import time
import board
import pwmio
# LED setup for most CircuitPython boards:
led = pwmio.PWMOut(board.LED, frequency=5000, duty_cycle=0)
# LED setup for QT Py M0:
# led = pwmio.PWMOut(board.SCK, frequency=5000, duty_cycle=0)
while True:
for i in range(100):
# PWM LED up and down
if i < 50:
led.duty_cycle = int(i * 2 * 65535 / 100) # Up
else:
led.duty_cycle = 65535 - int((i - 50) * 2 * 65535 / 100) # Down
time.sleep(0.01)
To use with QT Py M0, you must comment out led = pwmio.PWMOut(board.LED, frequency=5000, duty_cycle=0) and uncomment led = pwmio.PWMOut(board.SCK, frequency=5000, duty_cycle=0). Your setup lines should look like this for the example to work with QT Py M0:
# LED setup for most CircuitPython boards: # led = pwmio.PWMOut(board.LED, frequency=5000, duty_cycle=0) # LED setup for QT Py M0: led = pwmio.PWMOut(board.SCK, frequency=5000, duty_cycle=0)
Create a PWM Output
led = pwmio.PWMOut(board.LED, frequency=5000, duty_cycle=0)
Since we're using the onboard LED, we'll call the object led, use pwmio.PWMOut to create the output and pass in the D13 LED pin to use.
Main Loop
The main loop uses range() to cycle through the loop. When the range is below 50, it PWMs the LED brightness up, and when the range is above 50, it PWMs the brightness down. This is how it fades the LED brighter and dimmer!
The time.sleep() is needed to allow the PWM process to occur over a period of time. Otherwise it happens too quickly for you to see!
Fixed frequency outputs are great for pulsing LEDs or controlling servos. But if you want to make some beeps with a piezo, you'll need to vary the frequency.
The following example uses pwmio to make a series of tones on a piezo.
To use with any of the M0 boards, no changes to the following code are needed.
In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory CircuitPython_Essentials/CircuitPython_PWM_Piezo/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY drive should now look similar to the following image:
To use with the Metro M4 Express, ItsyBitsy M4 Express or the Feather M4 Express, you must comment out the piezo = pwmio.PWMOut(board.A2, duty_cycle=0, frequency=440, variable_frequency=True) line and uncomment the piezo = pwmio.PWMOut(board.A1, duty_cycle=0, frequency=440, variable_frequency=True) line. A2 is not a supported PWM pin on the M4 boards!
# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""CircuitPython Essentials PWM with variable frequency piezo example"""
import time
import board
import pwmio
# For the M0 boards:
piezo = pwmio.PWMOut(board.A2, duty_cycle=0, frequency=440, variable_frequency=True)
# For the M4 boards:
# piezo = pwmio.PWMOut(board.A1, duty_cycle=0, frequency=440, variable_frequency=True)
while True:
for f in (262, 294, 330, 349, 392, 440, 494, 523):
piezo.frequency = f
piezo.duty_cycle = 65535 // 2 # On 50%
time.sleep(0.25) # On for 1/4 second
piezo.duty_cycle = 0 # Off
time.sleep(0.05) # Pause between notes
time.sleep(0.5)
The following example uses a nice little helper in the simpleio library that makes a tone for you on a piezo with a single command.
To use with any of the M0 boards, no changes to the following code are needed.
To use with the Metro M4 Express, ItsyBitsy M4 Express or the Feather M4 Express, you must comment out the simpleio.tone(board.A2, f, 0.25) line and uncomment the simpleio.tone(board.A1, f, 0.25) line. A2 is not a supported PWM pin on the M4 boards!
To use with CircuitPython, you need to first install a few libraries, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory CircuitPython_Essentials/CircuitPython_PWM_Piezo_simpleio/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY drive should now look similar to the following image:
# SPDX-FileCopyrightText: 2017 Limor Fried for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""CircuitPython Essentials PWM piezo simpleio example"""
import time
import board
import simpleio
while True:
for f in (262, 294, 330, 349, 392, 440, 494, 523):
# For the M0 boards:
simpleio.tone(board.A2, f, 0.25) # on for 1/4 second
# For the M4 boards:
# simpleio.tone(board.A1, f, 0.25) # on for 1/4 second
time.sleep(0.05) # pause between notes
time.sleep(0.5)
As you can see, it's much simpler!
Wire it up
Use the diagrams below to help you wire up your piezo. Attach one leg of the piezo to pin A2 on the M0 boards or A1 on the M4 boards, and the other leg to ground. It doesn't matter which leg is connected to which pin. They're interchangeable!
Circuit Playground Express
Use alligator clips to attach A2 and any one of the GND to different legs of the piezo.
CPX has PWM on the following pins: A1, A2, A3, A6, RX, LIGHT, A8, TEMPERATURE, A9, BUTTON_B, D5, SLIDE_SWITCH, D7, D13, REMOTEIN, IR_RX, REMOTEOUT, IR_TX, IR_PROXIMITY, MICROPHONE_CLOCK, MICROPHONE_DATA, ACCELEROMETER_INTERRUPT, ACCELEROMETER_SDA, ACCELEROMETER_SCL, SPEAKER_ENABLE.
There is NO PWM on: A0, SPEAKER, A4, SCL, A5, SDA, A7, TX, BUTTON_A, D4, NEOPIXEL, D8, SCK, MOSI, MISO, FLASH_CS.
Trinket M0
Note: A2 on Trinket is also labeled Digital "0"!
Use jumper wires to connect GND and D0 to different legs of the piezo.
Trinket has PWM available on the following pins: D0, A2, SDA, D2, A1, SCL, MISO, D4, A4, TX, MOSI, D3, A3, RX, SCK, D13, APA102_MOSI, APA102_SCK.
There is NO PWM on: A0, D1.
Gemma M0
Use alligator clips to attach A2 and GND to different legs on the piezo.
Gemma has PWM available on the following pins: A1, D2, RX, SCL, A2, D0, TX, SDA, L, D13, APA102_MOSI, APA102_SCK.
There is NO PWM on: A0, D1.
QT Py M0
Use jumper wires to attach A2 and GND to different legs of the piezo.
The QT Py M0 has PWM on the following pins: A2, A3, A6, A7, A8, A9, A10, D2, D3, D4, D5, D6, D7, D8, D9, D10, SCK, MISO, MOSI, NEOPIXEL, RX, TX, SCL, SDA.
There is NO A0, A1, D0, D1, NEOPIXEL_POWER.
Feather M0 Express
Use jumper wires to attach A2 and one of the two GND to different legs of the piezo.
Feather M0 Express has PWM on the following pins: A2, A3, A4, SCK, MOSI, MISO, D0, RX, D1, TX, SDA, SCL, D5, D6, D9, D10, D11, D12, D13, NEOPIXEL.
There is NO PWM on: A0, A1, A5.
Feather M4 Express
Use jumper wires to attach A1 and one of the two GND to different legs of the piezo.
To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!
Feather M4 Express has PWM on the following pins: A1, A3, SCK, D0, RX, D1, TX, SDA, SCL, D4, D5, D6, D9, D10, D11, D12, D13.
There is NO PWM on: A0, A2, A4, A5, MOSI, MISO.
ItsyBitsy M0 Express
Use jumper wires to attach A2 and G to different legs of the piezo.
ItsyBitsy M0 Express has PWM on the following pins: D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, L, A2, A3, A4, MOSI, MISO, SCK, SCL, SDA, APA102_MOSI, APA102_SCK.
There is NO PWM on: A0, A1, A5.
ItsyBitsy M4 Express
Use jumper wires to attach A1 and G to different legs of the piezo.
To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!
ItsyBitsy M4 Express has PWM on the following pins: A1, D0, RX, D1, TX, D2, D4, D5, D7, D9, D10, D11, D12, D13, SDA, SCL.
There is NO PWM on: A2, A3, A4, A5, D3, SCK, MOSI, MISO.
Metro M0 Express
Use jumper wires to connect A2 and any one of the GND to different legs on the piezo.
Metro M0 Express has PWM on the following pins: A2, A3, A4, D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, SDA, SCL, NEOPIXEL, SCK, MOSI, MISO.
There is NO PWM on: A0, A1, A5, FLASH_CS.
Metro M4 Express
Use jumper wires to connect A1 and any one of the GND to different legs on the piezo.
To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!
Metro M4 Express has PWM on: A1, A5, D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, SDA, SCK, MOSI, MISO
There is No PWM on: A0, A2, A3, A4, SCL, AREF, NEOPIXEL, LED_RX, LED_TX.
Where's My PWM?
Want to check to see which pins have PWM yourself? We've written this handy script! It attempts to setup PWM on every pin available, and lets you know which ones work and which ones don't. Check it out!
In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory CircuitPython_Essentials/PWM_Test_Script/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY
# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""CircuitPython Essentials PWM pin identifying script"""
import board
import pwmio
for pin_name in dir(board):
pin = getattr(board, pin_name)
try:
p = pwmio.PWMOut(pin)
p.deinit()
print("PWM on:", pin_name) # Prints the valid, PWM-capable pins!
except ValueError: # This is the error returned when the pin is invalid.
print("No PWM on:", pin_name) # Prints the invalid pins.
except RuntimeError: # Timer conflict error.
print("Timers in use:", pin_name) # Prints the timer conflict pins.
except TypeError: # Error returned when checking a non-pin object in dir(board).
pass # Passes over non-pin objects in dir(board).
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