Rotary Encoding for Amateurs

sonicfire · Joined: 11 Feb 2007 Posts: 19 Location: Cedar Rapids

Does anybody have experience with rotary encoders for measuring a motor's rotational speed? I'm using a slotted-optocoupler as a rotary encoder to help me determine a dc motor's speed. The optocoupler delivers about 2V with no obstruction and about 0V when it's blocked. I could probably use an amplifier to make it 5V output if necessary. At any rate, I was wondering how I could write a reliable speed measurement program for the PIC 16F877. Does anyone know where there's some example code?

Thanks!

jma_1 · Joined: 08 Feb 2005 Posts: 147 Location: Wisconsin

Greetings,

A frequency example, 'EX_FREQC.C', ships with the CCS compiler (examples folder). I would include external circuitry to ensure the correct digital state (2V slightly low and will probably be indeterminate for a level change).

Consideration -> if your motor is stalled or not moving, the timer rollover conditon might need to checked

Cheers,
JMA

kd5uzz · Joined: 28 May 2006 Posts: 56

This doesn't help you with code, but it is a neat system.
I think I'm going to employ something similar to this in my next project...
http://www.seattlerobotics.org/encoder/200109/dpa.html