One of 10 educational circuit boards we designed for a private training institution. The circuit uses a voltage divider formed by a photoresistor (LDR) and an adjustable trimmer; when it gets dark, this voltage triggers a transistor, which directly lights an onboard indicator LED. Unlike the relay-based version, no external device is controlled here — only the circuit's own LED lights up — making this a simpler, entry-level example for teaching light-sensor logic.
Our customer's goal was to teach students light-sensing logic and the basics of transistor switching through a simple example, before moving on to the relay-based, more complex circuit. We handled the full schematic and PCB design ourselves, and made sure an adjustable trimmer lets the exact darkness threshold be fine-tuned.
After the needs analysis, we designed the circuit combining an LDR-based voltage divider, a transistor switching stage, and a current-limited indicator LED, adding a trimmer for sensitivity adjustment. We improved the circuit's robustness with a reverse-polarity protection diode on the power input. We delivered the schematic and PCB design to the training institution.
