Need a Transmitter-Receiver circuit

[Ejaz]

I need to transmit a 500 hz square wave without interference upto a distance of 50~60 meters that has to be picked up by the receiver at the other end. For this I need to have a transmitter-receiver circuit. Could someone plz help with a schematic! Thanks in advance!

 

[Lewish]

Is 500Hz the frequency you want to transmit at?
Or is 500Hz the resultant signal you want at the receiver?
What do you mean by "without interference"?
Is this inside a building or out in space?

 

[Ejaz]

I have designed a sensor in which light from LED (main) is detected by a Photodiode (PD). The received signal is then filtered and is made to flash an LED (indicator) when the received signal goes above a threshold voltage. The main LED is driven by a 500 hz squre wave signal. This whole thing is built as one unit. Now I want to separate this into two parts. One part will contain the LED (main), (PD) and the transmitter (to be built). The other part will have the receiver and the rest of the circuits. My objective is to transmit the 500 hz signal received by the PD to a distance of 50~60 meters without distortion. This will be used inside a building.

 

[Ejaz]

I made a mistake. The signal is a 500 hz pulse, not square wave.

 

[Lewish]

One way to approach such a requirement is to use frequency shift keying. You use a carrier of some frequency, and when the pulse is detected the carrier is shifted to some higher frequency that is easy to filter from the carrier. Then you just use a diode detector and lowpass filter to strip the 500Hz off the higher frequency.
This approach gives you some immunity from interferring signals.
You might want to try a 9MHz carrier that is shifted to 10.7MHz during pulse detection. 10.7MHz filters are easy to find.
Just one possible solution.

 

[nbucska]

If you just need one, Radio Schack ( may be misspelled !)
has a 40Khz modulated IR receiver which is able to
work for that distance even without additional optics. <nbucska@pcperipherals.com>