babar....

i experimented with the LOOP and the sensor.... what's happening is that there is always 4 or 5V in the Loop which is always appearing to the pins of the 8051. ofcourses there is a network of resisteros in between the LOOP and the 8051 pins. let me recall the circuit

+12V is connected to 1K resistor.
then comes the LOOP
after the LOOP there is 10K resistor
then there are two leads
one lead connected to GROUND through 10K resistor
other lead connected to 8051 pin.

so there is always +4V on the pin

sensor output is connected to LOOP which always produces +5V's

so still there is 4-5V on the pin

now if the sensor senses some thing.... i think the output of the sensor FLOATS that is atleast it does not SINK the current.


there is only 0V on the pin of 8051 when i connect the LOOP directly to the GROUND.

so if the sensor produces GORUND instead of FLOATING signal then the circuit will work fine



Shahzad