I am using an infrared tx-rx circuit as a speed sensor for my project. the equipment used are infra red led, an infrared receiver module and resistors. the fact is that when i use the the circuit, i only get a high output from the infrared rx irrespective of whether when the IR led is on or off. I don't know which one is faulty and moreover do I need to know more about IR Tx-Rx circuits since i have already change the led and Rx module twice?