[Solved] HC-SR501 PIR onboard LDR
I intend to solder an LDR onto HC-SR501 breakout board.
Has anyone done this and if yes, what size LDR did you find optimal. I have got a selection of LDRs lying around from 0.5M to 10M. Internet was not very helpful on this matter, as I couldn't find a manufacturer's datasheet.
A ballpark figure would be good, as I don't want to solder and de-solder a pot to the board just to find the correct threshold.
The LDR pins is connected to ground and is in series with an resistor of 1MΩ connected to the 3.3V supply. The LDR and the resistor form a voltage divider :
- if the LDR has a resistance of higher than 250K, the controller will turn on
- if the LDR has a resistance lower than 250K, the controller will turn off
So the LDR should read 250K at the switching light level so the best way is to measure it on a multimeter.
The 600 series had rubber skin. We spotted them easy, but these are new. They look human... sweat, bad breath, everything. Very hard to spot.
Thanks for your reply.
I have now found and attached a useful datasheet for the CMOS chip on the PIR breakout board.
It took a while, but I finally figured out where the 250000Ω fits into the equation!