HC-SR501 PIR Motion Sensor Adjustable - 3.3V TTL Output

The HC-SR501 provides a digital 3.3V TTL output signal. When motion is detected, the output pin goes HIGH (3.3V); otherwise, it remains LOW (0V). This logic level is compatible with most 3.3V microcontrollers like ESP32 or Raspberry Pi GPIO. For 5V systems like Arduino Uno, the signal can typically be read directly, but using a level shifter is recommended for long-term reliability.

Use the two onboard potentiometers. The sensitivity potentiometer (often labeled 'Sx') adjusts the detection range: clockwise increases distance (up to ~7m), counter-clockwise decreases it (down to ~3M). The time delay potentiometer (labeled 'Tx') sets how long the output stays HIGH after detection: clockwise increases hold time (up to ~200s), counter-clockwise decreases it (down to ~5s). A small screwdriver is required for adjustment.

The trigger mode is set by the rear Jumper. In single-trigger mode (Jumper on 'L'), the module outputs one pulse per detection event, ignoring further motion during the output delay period. In repeatable-trigger mode (Jumper on 'H'), the output will remain high as long as motion is detected within the delay window, and the timer resets with each new motion. Single mode is best for counting events; repeatable mode is ideal for keeping a light on while a room is occupied.

The 2.5-second blockade (or lockout) time is a fixed interval after the output goes LOW during which the sensor is unresponsive to new motion. This prevents output oscillation and false triggering from sensor noise or residual heat signatures immediately after an event. It is a hardware-based feature and is not adjustable, unlike the configurable delay time.