Shahzad,

I am not sure about your main target, but you can recieve the signals from all your devices by RS232.
To do this you have to take single MAX232 chip for receiving side of every device and connect receiver pin & TTL input & TTL output together. Then connect the RS232 output pin to main controller receiver pin and connect the RS232 input pin to the same RS232 output pin of another remote device etc. In the end you get the serial line to receive all signals of your devices. Of course, you have to write an appropriate software.

And as Andy Neil wrote, you can easily do single-transmitter-to-multiple-receivers.

Only one thing, all chips on receiving side must be powered all time. The written above is only idea you can modify it at your needs.

Hope it helps.

Regards,
George