I recently bought an HC-SR505 Mini PIR sensor. I connected its positive to my Arduino UNO's 5v, output to digital pin 2, and ground to ground. I used Adafruit's code to test it, but all the serial monitor displayed was "Motion detected", which meant the PIR was always on a HIGH state. I then also tried powering it using 3V3 but the PIR kept on cycling on a HIGH and LOW state. Any help on getting my sensor to actually work would be greatly appreciated.
I have similar problem with the HC-SR505 sensor. First few seconds it holds 0 on the output pin, and then always 1. I think it was bad batch of sensors. Bad batch in chinese manufacturing means thousands (or hundreds of thousands) bad modules flooded the market.
Meanwhile I decided to choose one of options:
- Stick with HC-SR501 sensor. It's bigger but works more or less.
- Buy expensive ($5.90) PIR sensor from seeed.
- Build my own PIR module by my required dimensions and function (in progress).
Update: From 5 sensors received 2 do the job. Supply voltage must be 5V or higher. First 20-60 seconds the output is not reliable and should be ignored. Then it works OK (if it works at all). Since the module has 3.3V LDO onboard the output signal is 3.3V.