One of 10 educational circuit boards we designed for a private training institution. The circuit monitors a capacitive touch module (TTP223B); when a touch is detected, it triggers a transistor that energizes a 5V relay. The relay output in turn drives a solenoid lock, releasing the door. Flyback protection diodes were added for both the relay coil and the solenoid.
Our customer's goal was to teach students how capacitive touch sensors are used, the logic of driving a relay through a transistor, and how an inductive load (a solenoid) is safely switched, through a concrete access-control example. We handled the full schematic and PCB design ourselves, making assembly easy to follow for students.
After the needs analysis, we designed the circuit connecting a capacitive touch module to a transistor switching stage and a relay output. We added separate flyback protection diodes for the relay coil and the solenoid lock, plus a reverse-polarity protection diode and filter capacitors on the power input. We delivered the schematic and PCB design to the training institution.
