Input from photocoupler

[khansaab]

This is a simple circuit in which PIC16F628A is counting pulses, converting the number of counts in ASCII and sending the ASCII data to LCD. LCD is working. Even counter is functioning if a direct on the pin is given. But, if pulses are sent through a photo coupler, then the pin (and output of photo coupler doesnt go high). However, if photocoupler is disconnected from PIC then it functions as normal, but when connected with PIC, the output doesnt changes its state. Circuit is attached. Please check if I am doing something wrong.

 

[LTX71CM]

Try this

**broken link removed**

 

[khansaab]

Unfortunately, this configuration is also not working. And that pin is programmed to function as counter and it is functioning if a direct high is given on it. But no other combination of transistor or photo coupler is working to produce a high on it.

 

[colin55]

Put digital multimeter on the collector of the transistor of the opto-coupler and let us know the voltage of the two states.

 

[be80be]

Whats the part number for your opto-coupler some don't need outside resistor and will not turn on.
And if it needs one 470 is way to high most need 50ma to light the led in them to turn the npn on
change it to 100 to 120 ohm and see if that works

 

[khansaab]

The system has started responding now. It was some compiler trouble. Regenerating the hex file fixed it. But now some other problems are at hand. I am working working them at the moment. Hope fully, I wont have to bother you guys with it.