ESET 350: Infrared Light Barrier
Published:
For our ESET 350 final project, we constructed and analyzed the MK120 Infrared Alarm System. This system is designed to establish an invisible, continuous optical link between a dedicated transmitter board and a receiver circuit, acting as a reliable tripwire security system.
To operate effectively without false triggering from ambient sunlight or room lighting, the transmitter modulates an infrared (IR) light beam at a specific high frequency of roughly 4.8 kHz using an astable multivibrator circuit. The receiver utilizes a phototransistor to constantly monitor for this exact frequency. As long as the receiver detects the pulsed IR light, the system remains in a passive state. However, when an object breaks the line of sight, the system immediately emits a loud audible alert and visual warning.
Beyond physical through-hole PCB assembly, this project involved extensive circuit analysis and validation. We captured detailed DC bench measurements and oscilloscope waveforms to analyze the performance of the astable multivibrator, LED driver transistors, and phototransistor outputs under various conditions.