[AVR] Atmega8 Digital input using 4n35 optocoupler

[asking]

I want to take the field Digital inputs using opto-coupler 4n35 as i have show in the above schmatic. But such arrangement is not working with Atmega8 in the Real hardware. I don't know the reason...actually when i check with multimeter. when the led source is on the PIN5 reads 60mv and when the led source of 4n35 is off it reads 5.0V. but when i connect this 5v as show in the schmatic to atmega8 it's not detecting...

so any other circuit idea of reading field digital inputs via 4n35 (optical isolation)?

Thanks...

 

[KlausST]

Hi,

Set the port to input by writing a "0" to the corresponding "ddrb" bit.

Read in by using "pinb".
You will see a low, when optocouplercis active.

Hope this helps
Klaus

Added: ..and be sure that your programmer does not overwrit the mosi pin.

 

[asking]

Hi,

I found the problem. It was DDRB bit which was set to be in output direction. DDRB = 0xFF; but still i was able to use external push button with no issues. That's strange. But as soon as i made it DDRB = 0x00; i am able to detect the opto-coupler signal and now my circuit is optically isolated.

Thanks