RPi.GPIO 0.5.2a now has software PWM – How to use it #piday #raspberrypi @Raspberry_Pi

PWM squarewave

RPi.GPIO 0.5.2a now has software PWM – How to use it, from RasPi.TV:

Over the last couple of weeks the pace of development for Python programmers who like to dabble in GPIO has gone up a gear. Both main GPIO systems for Python on the Raspberry Pi have been getting some enhancements.

RPi.GPIO, now at version 0.5.2a, has interrupts and threaded callback capability. You will probably have seen my three recent posts showing how to use those.

WiringPi for Python version 2 is in Beta testing. I discovered two bugs while I was trying it out. Both of those have been squashed. One by Gordon “Drogon” Henderson in the C source code and another by Phil “Gadgetoid” Howard in the Python install script. There’s a lot more stuff to test, but that’s not what I’m writing about today, so I’ll save that for a future post. Suffice it to say that the Python Gertboard software all works with WiringPi2 (at least it will when I release it soon with very minor tweaks).

So what? Why would I care about PWM?

It’s kind of useful. Let’s back up for a minute in case anyone doesn’t know what it is/does. PWM is pulse-width modulation. Put simply, this is a signal that is switched between on and off, usually rather quickly.

Do you remember when you were a kid, how you sometimes flicked the light switch on and off repeatedly, really quickly, to see what would happen? And you were told not to do it in case something bad happened (and it never did)? That was crude PWM.

It’s a “square” waveform (on or off most of the time) and looks something like [the photo at the top of this post]….

It’s used for controlling a variety of devices – motor speed, servo* positions and other things. You can even use PWM to vary the brightness of leds by switching them on and off at varying frequency and duration.

There are two important parameters that determine PWM…

  1. Frequency
  2. Duty cycle


Frequency, in Hertz (Hz) is the number of times per second that a pulse is generated. This counts from the start of one pulse to the start of the next. i.e. from when the pulse starts to rise, to the next time it starts to rise. So it includes all the “on” time and “off” time and “in between” time for one complete wave cycle.

Duty Cycle

Duty cycle is the percentage of time between pulses that the signal is “high” or “On”. So if you have a frequency of 50 Hz and a duty cycle of 50%, it means that every 1/50th (0.02) of a second a new pulse starts and that pulse is switched off half way through that time period (after 1/100th or 0.01s)….

Read more.

998Each Friday is PiDay here at Adafruit, be sure to check out our posts, tutorials and new Raspberry Pi related products. Have you tried the new “Adafruit Raspberry Pi Educational Linux Distro” ? It’s our tweaked distribution for teaching electronics using the Raspberry Pi. But wait, there’s more! Try our new Raspberry Pi WebIDE! The easiest way to learn programming on a Raspberry Pi.

We now have Raspberry Pi Model B with 512MB RAM in stock and shipping now!

Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards

Join Adafruit on Mastodon

Adafruit is on Mastodon, join in! adafruit.com/mastodon

Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.

Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Join over 36,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org

Maker Business — “Packaging” chips in the US

Wearables — Enclosures help fight body humidity in costumes

Electronics — Transformers: More than meets the eye!

Python for Microcontrollers — Python on Microcontrollers Newsletter: Silicon Labs introduces CircuitPython support, and more! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi

Adafruit IoT Monthly — Guardian Robot, Weather-wise Umbrella Stand, and more!

Microsoft MakeCode — MakeCode Thank You!

EYE on NPI — Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — #NewProds 7/19/23 Feat. Adafruit Matrix Portal S3 CircuitPython Powered Internet Display!

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at AdafruitDaily.com !

1 Comment

  1. There will be a part 2 to this article with some practical examples. This PWM isn’t accurate enough for servos (too jittery), but should be fine for led dimming and motor control (where it doesn’t much matter if it skips a beat or two).

Sorry, the comment form is closed at this time.