How do I count pulse width ?

ac34856 · Joined: 14 Dec 2009 Posts: 33 Location: Wales

I am reading an encoder for velocity and I would like to calculate the speed using the encoder pulse width.

I have tried doing this using an External Interrupt INT_EXT to start timer 1
but couldn't work out how to stop the timer on the falling edge so that the count relating to pulse width (and hence velocity) could be read.

Of course if the shaft isn't moving it will also need to cater for this and time out within 1 second for example.

Any help would be appreciated -

Rob

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The CCP (in capture mode) is designed to do this.
CCS has an example file which uses both CCP modules to do it:

ac34856 · Joined: 14 Dec 2009 Posts: 33 Location: Wales

Yes that routine was tested yesterday and works mostly ok above
500Hz.

If I wanted to count very slow pulses say down to 10Hz it
would need to wrap around which obviously means more bits
counting resolution.

In its present form it works ok down to above 100Hz after which
the counter gets into trouble.

Ideally I would need to increase the counter resolution to 32 bits
is there a quick way to do this ?

Rob