Simple C app for driving Binary Clock Shield for Raspberry Pi
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This is my simple C app that drives my Binary Clock Shield for Raspberry Pi.

To use this, you'll need to have a Raspbian install built and running on your Raspberry Pi (I would recommend using the latest "Raspbian Lite" as there's no need of X-Windows, but that's just me).

You need to have installed Mike McCauley's excellent BCM2835 library first (from That's the only dependency.

If you're using one of the oldest Raspberry Pis (probably with a 26-way GPIO connector) then you'll need to change a constant near the top of the code. This is because the GPIO pin arrangement was changed after the first version of the Pi was released. It's not a hard change - there's a comment next to it.

To compile, enter: gcc -o bcd-clock bcd-clock.c -l bcm2835

To run it: ./bcd-clock [brightness]

... where [brightness] is a number between 1 and 15. It defaults to 8.

If you want your clock to run on startup, then add this line near the end of your /etc/rc.local file:

/home/pi/bcd-clock 15 &

(The '&' forces it to the background.)

See my blog post on this project, here: It includes more detailed notes about installation.