Sampling issue

jacqueskleynhans · Posted: Fri Aug 29, 2008 2:01 pm

Hi i need to sample my adc channel fast. I have accelerometer connected to it measuring vibration. Highest spectral component is 1.3k. Need to measure 3 times nyquist at 4k amounts to 250 microseconds. Need to use an interrupt. Question.
Can i use timer0 like this where i simply read the two_fifty_microsecond and when its true i do my adc routine ?

#byte timer0low = 0xfd6
SETUP_TIMER0(RTCC_INTERNAL|RTCC_8_BIT|RTCC_DIV_1);

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

When the timer interrupt occurs, it will interrupt the main code and go
do the timer interrupt code. When that routine is finished, the program
will resume executing the main code right at the point where it left off
when it got the timer interrupt. That's how interrupts work.

I suggest that you don't use interrupts for the initial testing of your code.
Just make a "for" loop in main(), and put in a 250 us delay (or a little bit
less, to account for the time spent in the loop), and do all your A/D
sampling in that loop. Store the A/D samples in an array. Then when
the loop is done collecting samples, you can do some math on the data
you have collected.

It's easier to do this if you start with simple code.

jacqueskleynhans · Posted: Fri Aug 29, 2008 3:07 pm

ill give that a try.
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RayJones · Posted: Fri Aug 29, 2008 4:10 pm

I always find it useful to generate a blip on one of the pins so you monitor the sampling period with an oscilloscope.

Simply use something like