[sdiy] Rotary encoders: is there a clever way to handle many?

Hugh Blemings hugh at blemings.org
Mon Aug 10 14:06:03 CEST 2015


On 10/08/2015 21:45, Rick Jansen wrote:
> Well, that was fun, or was it. Handling a rotary encoder with an Arduino
> can be done, but there's a lot to take care of! The signals from my
> (simple) €1,50 encoder bounce all over the place. My current
> implementation uses one of the two interrupt pins of the Arduino,
> although a polling solution is possible as well. I'm not sure if it is
> because of the "quality" of this encoder, but at times there are nearly
> as many pulses clockwise as anti-clockwise..  I ended up counting both
> clockwise and anti-clockwise pulses, the greater of which determines
> actual direction. Even an "acceleration" is detected, if you turn the
> rotary fast the value will change more dramatically.
> It works quite well, but at the same time I wonder how other machines
> work, that track 8 or 16 rotary encoders.. An Arduino Mega has many more
> interrupt pins than the measly Arduino Uno, but still. Is there a clever
> trick to track many rotary encoders that I am missing?

I haven't done this for a loong time, but back on the 68HC11 when I did 
a similar thing it had to be a polling system as there weren't 
sufficient interrupt pins for each encoder.

Fed the outputs of each encoder into parallel input pins.  Four encoder 
per 8 bit port, but one could presumably multiplex them too.

I seem to recall a scan rate of a kHz or so, a state machine that 
changed based on the previous and current state of each encoders 
quadrature output pins did the trick and would deal with the debounce as 

With a little trickery the same state machine code could be used for 
each encoders' pair of pins, some bit shifting to turn it into a two bit 
value that the state machine logic could use with the assembly 
equivalent of a C switch() statement.

Above is a bit rambly, but might point you in the right direction, if 
not I'm sure smarter minds than mine will interject :)


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