Hi Shahzad,

You Said:

when sensor produces 0 V's there is still+5V on the 8051 pin. what should i do.....
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Have you ever noticed what will happen if connected the set pin of micro (at +5) directly to ground .......

Try to find it and you will know what will happen when sensor produces 0V connected to the micro port at +5V


Good Luck

Babar

PS: by the way what do you mean sensor producing 0V, is it that the sensor gives ground out ...... or what