I assume you are using an ADXL202 or something similar, as we use in our
performance meters.  I would recommend going with the CCP inputs.  Connect
one axis to one input, the other to the other input.

Reset the timer value so you can get two measurements without overflowing
(makes the sums easier)
Set the first CCP input to trigger on a rising edge, store the value
Set the first CCP to trigger on a falling edge, store the timer value
Repeat for the second CCP input.

Period is the length between the middles of the two CCP input pulses, and
the width of each one divided by the period gives you the duration.  You
will need to calibrate each device for it's 0g position and 1g range to get
a useful reading.  The pulsewidths are such that you should have no problem
in doing this as the pulses are never really short.  DON'T measure the
period as the time between the starts or ends of each pulse as that is not
correct, it must be done to the middle.

Hope that helps.

Regards,

Martin


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Agent0013
Sent: 24 October 2002 17:27
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: Help with reading two PWM signals.


I am somewhat new at using microcontrollers, but very experienced at
programming and electronics. I am working on a senior design project for
school and I either need to read in two pwm signals or two analog
signals. This is coming from a two axis accelerometer from Analog Devices.

I think I would prefer to read the pwm since it is already in a digital
form and skip the A/D conversion. Would A/D be better than pwm?

If reading pwm, how do I read the two separate signals and get their
duty cycle of each? Do I use an interrupt? How do I interrupt on two
separate signals? I read some on the list about the interrupt on change
and that sounds like too much trouble. Or just poll the pins constantly
until I read a change and then see how much time passed?

As long as I am writing, any suggestions on which chip to use would be
great also.

Any help and suggestions on this would be greatly appreciated.

Thanks,
Justin Barth

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads