Record, storage and compare analog signals

[Kuba230]

Hi, all, please I need help
I need record analog signal (10Bit) to PIC with length 60us, storage as reference (red line) and compare with next one incoming (blue line). My question is, how to sampling and storage reference signal and compare those signals? I want to use PIC18F2455.
Look Fig1
Thanks Kuba

[Ioannis]

Looking at the Data sheet of the chip 18F2455 and especially in the A/D Acquisition Requirements, it seems that you need a 2.45usec for every sample. Of course you need also a little time to transfer the AD value to an array and start AD again. Say for the sake of the discussion the the total time is 3usec.

This leaves you with only 20 samples in the 60usec period.

Is that OK with you?

Ioannis

[Kuba230]

I think, 20 samples is enough.
How can I obtain this 20 samples and storage as numbers for calculation?

Thanks Kuba

[Ioannis]

The assumption of 2.45us was based on the fact that Vdd is 5Volts and the source impedance less than 2.5Kohm.

What will be the clock of the your controller?

Ioannis

[Kuba230]

I will use osc. 20MHz

Kuba

[Ioannis]

Lets then suppose you have the analog input at AN0.

ADCON0=%00000001    ' Channel 0, ADC on
ADCON1=%00001110    ' AN0 as analog,rest as digital
ADCON2=%10010101    ' Right justify result and Fosc/16

analog_res_array    VAR WORD[40]
counter             VAR BYTE
start_array         VAR BYTE     ' first element of the array to store samples
stop_array          VAR BYTE     ' last element of the array to store samples

start_array=0:stop_array=19      ' first group of 20 samples
gosub adc_routine
start_array=20:stop_array=39     ' second group of 20 samples
gosub adc_routine

......

adc_routine:
    for counter=start_array to stop_array
        high adcon0.1
        while adcon0.1:wend
        analog_res_array[counter]=adresh*256+adresl
    next counter
return

Now in the array you have 40 samples (two groups of 20) and you can compare them.

Note that code is untested, but you get the idea.

Ioannis