This project enables PWM on the GPIO pins you request of a Raspberry Pi. The technique used is extremely efficient: does not use the CPU and gives very stable pulses.
This project is based on the excellent work of Tomas Sarlandie pi-blaster: https://github.com/sarfata/pi-blaster and the modifications/updates made by Michael Vitousek: https://github.com/mvitousek/pi-blaster
Pi-blaster project is based on the excellent work of Richard Hirst for ServoBlaster: https://github.com/richardghirst/PiBits
How to build and install
This project is only distributed as source files. The build environment is based on Autotools to allow for compilation on the Raspberry Pi, or cross-compilation.
You may need to install 'autoconf' to build. On Raspbian and other Debian based systems this can be achieved with:
sudo apt-get install autoconf
Building is extremely simple:
./autogen.sh ./configure make
To start pi-blaster and have it relaunched automatically on every reboot:
sudo make install
How to start manually
To start pi-blaster manually run:
How to uninstall
sudo make uninstall
This will stop pi-blaster and prevent it from starting automatically on the next reboot.
How to use
pi-blaster creates a special file (FIFO) in
/dev/pi-blaster. Any application on your Raspberry Pi can write to it (this means that only pi-blaster needs to be root, your application can run as a normal user).
Important: when using pi-blaster, the GPIO pins you send to it are configured as output.
To set the value of a PIN, you write a command to
/dev/pi-blaster in the form
<value> must be a number between 0 and 1 (included).
GPIO number Pin in P1 header 4 P1-7 17 P1-11 18 P1-12 21 P1-13 22 P1-15 23 P1-16 24 P1-18 25 P1-22
Examples: Turning PWM pins ON
To completely turn off GPIO pin 17:
echo "17=0" > /dev/pi-blaster
To completely turn on GPIO pin 17:
echo "17=1" > /dev/pi-blaster
To set GPIO pin 17 to a PWM of 20%
echo "17=0.2" > /dev/pi-blaster
Examples: Turning PWM pins OFF (releasing a pin so it can be used as digital GPIO)
To release previously turned ON GPIO pin 17:
echo "release 17" > /dev/pi-blaster
NodeJS users can use pi-blaster.js.
How to adjust the frequency and the resolution of the PWM
On startup, pi-blaster gives you the frequency of the PWM, the number of steps that you can control, the maximum and the minimum period of a pulse.
sudo ./pi-blaster Using hardware: PWM Number of channels: 8 PWM frequency: 100 Hz PWM steps: 1000 Maximum period (100 %): 10000us Minimum period (0.100%): 10us
You can adjust those by changing a few defines at the top of the source code:
NUM_SAMPLES: The number of steps
SAMPLE_US: The time of one step (minimum period)
If you do not neet a resolution of 1000 steps (approximately equivalent to a 10 bit DAC), then you can reduce the number of samples or increase the duration of the steps.
Richard Hirst who wrote the original code recommended not going below 2us for
To use the BCM2835's PCM peripheral instead of its PWM peripheral to time the DMA transfers, pass the option:
This is useful if you are already using the chip's PWM peripheral, for example for audio output.
To invert the pulse (off = pin HIGH, pulse = pin LOW), use:
This can be useful for common anode LEDs or other devices that expect an active-low signal.
To view help or version information, use:
Warnings and other caveats
Pins being used by pi-blaster will be configured as outputs. Do not plug something on an input or you might destroy it!
This daemon uses the hardware PWM generator of the raspberry pi to get precise timings. This might interfere with your sound card output.
There is experimental support for a PCM time-source. If you are interested, I suggest you look at Richard Hirst original project (ServoBlaster) and try the
A practical example: high-power RGB lighting
This library was developed for TBideas high power LED driver. You can read more about this project on our blog.
Want to support this project?
The best way to contribute is to write code for the features you would like to see and to make a pull-requests.
Another way is to send DogeCoin donations to D7pQ9CoUepazpGbwxgiaGPCMBk8i66u4yE. Donations will be used to help promote hardware hacking. For example by giving away servos and led strips during hackathons.
Released under The MIT License.
Note: This project was initially released by Richard Hist under the GPL v3 License. Richard gave me explicit permission to distribute this derivative work under the MIT License.
Copyright (c) 2013 Thomas Sarlandie - Richard Hirst Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.