Introduction
Before connecting a PIR sensor to your microcontroller, it’s wise to test it independently. A multimeter is all you need to verify power, output, and basic functionality.
What You’ll Need
- Digital multimeter (any basic model)
- PIR sensor (e.g., HC-SR501)
- Power supply (battery or USB power with appropriate voltage)
- Jumper wires
Step 1: Visual Inspection
Check the sensor board for any physical damage, cold solder joints, or missing components. Ensure the Fresnel lens is clean and properly seated.
Step 2: Power the Sensor
Connect VCC and GND to a suitable power supply (5V for HC-SR501, 3.3V for AM312). Use a breadboard or simply hold wires in place. Allow 30-60 seconds for warm-up.
Step 3: Measure Supply Voltage
Set your multimeter to DC voltage (20V range). Place probes on VCC and GND pins (on the sensor itself). You should read the supply voltage (e.g., 5.0V). If significantly lower, your power source may be inadequate.
Step 4: Check Output Idle State
With no motion, measure voltage between OUT and GND. For most sensors, this should be near 0V (LOW). Some sensors may have a pull-up and output HIGH when idle – check datasheet. Typically HC-SR501 outputs LOW idle.
Step 5: Trigger the Sensor
Wave your hand in front of the sensor. The output voltage should jump to a HIGH level (typically 3.3V for HC-SR501). If using an analog multimeter, you may see the needle flicker. For digital, watch for a voltage change.
Tip: If the output doesn’t change, try adjusting sensitivity or waiting longer (warm-up).
Step 6: Test Repeatability
Trigger multiple times. The output should go HIGH each time and return to LOW after the hold time. Note the hold time (you can time it with a stopwatch).
Step 7: Check Potentiometer Function (if adjustable)
Turn the sensitivity pot and see if detection range changes. Turn the time pot and see if hold time changes. This confirms the pots are working.
Step 8: Test with a Load (Optional)
You can connect an LED with a current-limiting resistor (220Ω) between OUT and GND. When triggered, the LED should light. This confirms the sensor can source enough current (usually a few mA).
Troubleshooting with Multimeter
- No output change: Sensor may be defective, or lens may be blocked.
- Output always HIGH: Could be stuck (see troubleshooting article).
- Output flickers randomly: Possible interference or unstable power.
Testing Open-Drain Sensors
Some sensors (like Panasonic EKMB) have open-drain outputs. You’ll need a pull-up resistor (10k) between OUT and VCC. Then test as above.
Conclusion
A multimeter test quickly verifies if your PIR sensor is functional. It’s a valuable first step before diving into code.