Room Activity Sensing
Occupancy-responsive lighting with PIR motion detection and microcontroller-driven relay control.
2023
HC-SR501 · Motion input, control state and lighting output.
Motion-responsive lighting
An HC-SR501 PIR sensor supplies a motion signal to an Arduino Uno. The controller maps that input to a relay state controlling the light, connecting room activity directly to the switching decision.
Technology and role
Scroll horizontally to compare.
| Component | Role |
|---|---|
| HC-SR501 PIR | Detect motion and supply a digital input. |
| Arduino Uno · C++ | Read the input and select the lighting state. |
| 5 V relay · light | Translate the control signal into the switched lighting output. |
State transitions
- A high PIR signal selects the active lighting state.
- The relay module translates the controller output into the switched light state.
- When the PIR input returns low, the included control code selects the inactive lighting state.
- Repeated input checks connect new detections to the next control decision; the sensor event and relay output remain separate signals.
Engineering decisions and deliverables
The circuit uses a direct input-to-output state mapping, making motion detection and switching easy to trace. Relay control separates microcontroller signaling from the controlled lighting circuit. The project documentation includes the component architecture and a C++ control snippet that demonstrates the active/inactive transitions.