integration of values from ADC

[neurus]

hi

I've to do an integrator from 0 to 60 sec. Every 0,5 sec I get a new value from ADC. Doe's anybody have any idea?

I'm working with CCS and Pic 18f252.

Thanks

pablo

[neurus]

hi

how can I implement the trapezoidal rule for a Pic 18f252? Can help me anybody?
Thanks

Pablo

[Ttelmah]

Do you really mean an 'integrator'?. If you feed a DC valtage into a pure integrator, you will just end up with the output eventully going over/underscale. The same will happen with a software version, unless you code relative to the mean signal level.

Probably the easiest 'averaging' algrithm, is this:

[SherpaDoug]

I have never heard of a "trapezoidal rule." But if you want to do a "boxcar" filter you must store every reading in the sample so it can be removed when it is too old. That is RAM intensive.
Consider if you really need a FIR (finite impulse responce) filter, or can you get away with an IIR (infinite impulse responce) filter like Ttelmah suggested. IIR is much easier.
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[Ttelmah]

I was going to suggest in my original post, that you can do a 'rolling sum' filter (have done this myself in the past). With this, for the 120 sample example, you implement a buffer, using one wrapping pointers. Then when a new value arrives, you retrieve the old value which would be overwritten (120 samples ago), and subtract this from the 'sum', add the new value to the sum, and then save the new value into the buffer at the same location, then increment the pointer. Though this still means you have to hold 120 values, you don't have to regenerate the 'sum' for every moment in time. If you have your input voltage 'offset' into the ADC input range, with zero at (say) 1024 counts, then store the value as a signed int16, subtract 1024 from the incoming number, and perform this arithmetic, you generate the trapezoidal waveform, that I think you are looking for.

Best Wishes