How to transmit a signal to a reciever over 50 meters?
I would recommend to use RF, since 50 meters are too much for simple infrared technology, and RF keeps being simple.

There are plenty example circuits to use by your own. Just search for RF Transmitter and Receiver.

http://pcbheaven.com/opendir/index.php?show=7471uk8807mj49773b5d