For some of the Radiodan applications Richard, Anton and I discussed on thursday at the Bristol Hackspace, we need a rotary encoder. For example, this 'Wrong (W)radio: Time Travel Radio can play audio from the last few days, navigating time by turning the right hand knob:

Image

I've not done much work with the Raspi GPIO, but Richard found an Adafruit example, and then I found this one, that looked simpler on the face of it - except that my C isn't exactly great, and doesn't in fact exist. Anyway it had a nice simple example of how to wire a rotary encoder to the Raspi (plus an explanation of the other two legs on my rotary encoder - they're for the built-in button).

After a bit of a struggle, I got it to work - the library needs wiringPi

git clone git://git.drogon.net/wiringPi
git pull origin
cd wiringPi
git pull origin
./build

then

git clone https://github.com/astine/rotaryencoder
cd rotaryencoder
nano test.c

contents of  test.c:

#include "stdio.h"
#include "rotaryencoder.h"
int main()
{
printf("Hello!\n");
wiringPiSetup () ;
/*using pins 23/24*/
struct encoder *encoder = setupencoder(4,5);
long value;
while (1)
 {
 updateEncoders();
 long l = encoder->value;
   if(l!=value)
   {
     printf("value: %d\n", (void *)l);
     value = l;
   }
 }
return(0);
}

Save and compile it:

gcc -lwiringPi program.c rotaryencoder.c -o test

Run it (GPIO stuff needs to be run as root): I was turning the rotary encoder anti-clockwise

sudo ./test
Hello!
value: -1
value: -2
value: -3
value: -4
value: -5
value: -6
value: -7
value: -8
value: -9
value: -10
value: -11
value: -12
value: -13
value: -14
value: -15

The wiring's like this:

Image