[MOVED] Bi-directional visitor counter problem

barry said:

Post a schematic!!!!! Tell us what you are using for a receiver!!!!

Click to expand...

My project is bidirectional visitor counter.I m havin problem somewhat like above..using 2pairs of IR LED & IR detector(photodiode),,o/p from detector are fed to inverting i/p of comparator LM324 & other i/p of LM324 is 10K ohm preset..then o/p from LM324 are fed to microcontroller AT89C51...LED & 7 segment coonected to microcontroller is continiously blinking even if there is no interruption beetween sensors!!..how to solve ??..help!!.project submission is knocking the door!:-(

thanks

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I tried to amplify the voltage I'm getting from reciever using lm324n..still doesn't work..

Barry is right. Any sort of schematic, even hand drawn and scanned to make .png or jpg would help lots.
The logic part, which pair signals first, counted while both are signalled together, is easy enough.
Your difficulty is getting reliable signal conditioning from the LED/photodiode pairs to deliver the change as a logic signal.

Without knowing the circuit, I can only suggest ..
1. Exclude unwanted IR from the photodetector. So shroud both the LED and the photodetector using some kind of tube/hood.
2. There is some distance across the path. Be sure of the range. The LED needs to be narrow beam
3. The photodiode might need some very simple optics to get the LED beam to focus on the photodiode.
4. Check the specification of the photodiode detector.
.. If just the diode, the circuit is different as for the more usual NPN or PNP transistor switch type output.
.. It needs to be biased via a resistor to extract the voltage change as the beam is cut.
5. Amplifying. Do you need to? If you do, you might need some simple RC filtering to exclude high frequency noise.
.. This is easy to add to an op-amp, often just by putting the right capacitor across the op-amp feedback resistor.
.. You only want to sense people passing. This happens at Hz - not kHz. So take the opportunity to clean up the signal.
6. Thresholding. Whatever is fed to the comparator, it must transit the voltage at the other comparator input.

Continuous blinking sounds like random noise triggering a transition - or maybe the micro-controller program is repeatedly looping some code. Try temporarily disconnecting the signal to the microcontroller, to check the blinking stops.

The very first thing is to check the code that is burn in microcontroller.