i have a problem with the infra led receiver
it produces when signal is transmitted square pulses
and when not transmitted 0 dc
i want to distinguish between the 2 cases ,one tob be +ve dc'and the other 0
If the voltage level of the square pulses is always much higher than the noise output with no signal, you can use a comparator and then a retriggerable monostable multivibrator with a period somewhat longer tha the time between the IR pulses.