This project enables PWM on all the GPIO pins 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 Richard Hirst for ServoBlaster: https://github.com/richardghirst/PiBits
How to build and install
This project is only distributed as source files. Building it is extremely simple.
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, all the pins are configured as output.
To set the value of a PIN, you write a command to
/dev/pi-blaster in the form = where must be a number between 0 and 1 (included).
Channel number GPIO number Pin in P1 header 0 4 P1-7 1 17 P1-11 2 18 P1-12 3 21 P1-13 4 22 P1-15 5 23 P1-16 6 24 P1-18 7 25 P1-22
To completely turn off pin0:
echo "0=0" > /dev/pi-blaster
To completely turn on pin1:
echo "1=1" > /dev/pi-blaster
To set pin1 to a PWM of 20%
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
All the pins 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.
Pete Nelson (https://github.com/petiepooo)
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.