RGB LED on Expansion Dock
I was looking around for information on the GPIO connected to the RGB LED on the expansion dock, didn't find any, so I tried to traced back using a multimeter. Below is the connection, please correct me if I'm wrong, otherwise at least this should help the next guy looking for it.
1kOhm current limiting resistors are connected to each pin
LED R - GPIO17 LED G - GPIO16 LED B - GPIO15
Set GPIO to 0 to turn on and 1 to turn off. I'm guessing the invert is because most GPIO have better sinking capability than sourcing. I would have expect a slightly different resistor value, especially for Red as each color have different luminosity and to achieve a better "white" when all are turned on.
Below is some code to get started
#Setup export and GPIO direction echo 17 > /sys/class/gpio/gpiochip0/subsystem/export echo 16 > /sys/class/gpio/gpiochip0/subsystem/export echo 15 > /sys/class/gpio/gpiochip0/subsystem/export echo out > /sys/class/gpio/gpio17/direction echo out > /sys/class/gpio/gpio16/direction echo out > /sys/class/gpio/gpio15/direction #turn off RGB LED echo 1 > /sys/class/gpio/gpio17/value echo 1 > /sys/class/gpio/gpio16/value echo 1 > /sys/class/gpio/gpio15/value #turn on R echo 0 > /sys/class/gpio/gpio17/value #turn on G echo 0 > /sys/class/gpio/gpio16/value #turn on B echo 0 > /sys/class/gpio/gpio15/value
Nice! That's some good detective work :)
We've actually made a tool that can run software PWM to control the colour of the LED. Check out this help desk article.
Lol, I was searching for RGB LED, no wonder I didn't find anything here and at the help desk. That's what I've been thinking, you guys wouldn't have missed such a simple thing.
Very nice work! Thank you very much. I am so stupid not realising that you needed a 0 to turn it on. Doh! Cheers!
The code for
expledused in the help desk article is here https://github.com/OnionIoT/fast-gpio/blob/master/scripts/expled.sh in case someone is looking.