problem with heart beat monitor

[binu.kr]

hai everybody
now iam working with a heart beat monitoring project in p16f877a...finger is used to detect the heart beat count....but it doesnt give actual count ..in one minits its counts more than 256...if we not place finger in sensor part its give proper count means '0'..but wen we place the finger between high intensity red led and ldr count is more than 256..i think fluctuations in the finger affecting the sensing part.. i dont know how to attach circuit diagram iam using LM358 and the 7th pin of lm358 is the sensor output ..iam connecting the 7 th pin to a ledand also to PORTC0 PIN BUT IAM NOT USING ANY PULL UP IN PORTCO PIN....CAN U PLAESE HELP ME TO SOLVE THIS PROBLEM
THIS IS THE CIRCUIT DIAGRAM LINK http://onlinetps.com/heartbeat.GIF


thankzzzzzzzzzzzzz in advance
_________________
nn

[umka]

Have you checked the output signal from the hardware on an oscilloscope to check the output is occuring at the expected rate?

[FvM]

Although it's a bad circuit to my opinion (threshold depends on LM358 offset voltage, missing hysteresis), what was the result when systematicly varying the gain and threshold adjustment?

[binu.kr]

Thanks for your valuable reply.
I don't have any oscilloscope. But now I'm given a pullup in RC0 and 100uf capacitor at the output pin of lm358. It improves the count approximately equal to 70 per minutes. But it not stable always, sometimes its varying.
_________________
nn

[FvM]

Why not using a linear AC amplifier and the PIC ADC as a programmable threshold detector?