LED-based Wake-up Circuit for Microcontrollers

This article proposes, analyzes, and tests a wake-up circuit for a microcontroller (MCU) that uses a light-emitting diode (LED), operating as a photodetector, illuminated by a smartphone flashlight. The wake-up circuit consists of a high-pass filter and a voltage-level translator that interfaces the LED, with a suitable resistor in parallel, to the MCU. When illuminated by a switching flashlight, the LED generates a square voltage that is conveniently converted in logic levels at the output of the wake-up circuit. A firmware embedded into the MCU additionally checks that a predetermined sequence of logic pulses at a given rate is accomplished to activate the MCU. This article includes a theoretical analysis and experimental results that validate the proposed circuit.