These questions relate to an IR Light curtain i am trying to build. The light curtain is going to be used to cut the power to an electrical testing bench when any of the curtains IR light beams are broken. The project will consist of IR transmitters ( IR LED's(zd1946)- data sheet-http://www.jaycar.com.au/products_uploaded/ZD1946.pdf), [Broken] IR Receivers (Photodiodes (zd1952)-data sheet- http://www.jaycar.com.au/products_uploaded/ZD-1952.pdf [Broken]), and the circuitry needed to connect them to the mains power and trip the power to the bench when an IR beam is broken. My questions relate to the connection of the IR receiver to a power supply and the wiring parameters i need to be aware of. 1. does there need to be a current limiting resistor between power supply and photo diode? 2. does the IR led need to be pulse width modulated, if so how? 3. what is the general wiring layout to power a photodiode that has a TTL level output, how can i use this TTL output to send a stop signal to the mains power supply of the bench? 4. any information that you think could be helpful in this situation would be great! I thank you for taking the time to read this rather long thread, and any help would be greatly appreciated.