Hi Circuiteers.

I have mounted a motion sensor (HC SR 501) on my dashboard and it transmits a signal when it detects motion to a receiver in my house. It was very quite overnight but went off a lot around 9am until I turned off the receiver. I can only think that the increased sunlight levels create lots of false positives. Has anyone had a similar experience and found a way round this? Are HC SR 501 usable at all in sunlit conditions, where cloud movement may create fluctuating IR levels?

Robin

 

hi Robin,
They do respond to sunlight and shadow, reflections from passing vehicles, bushes etc.
Does the PCB have a sensitivity control pot.?
E

 

hi Robin,
They do respond to sunlight and shadow, reflections from passing vehicles, bushes etc.
Does the PCB have a sensitivity control pot.?
E

There's the 2 pots on the HCSC501 board. I'll check that the sensitivity one is turned down to minimum and see how that goes

 

hi,
You should find this PDF helpful.

 

It's been a few days now. The sensitivity was half-way, but turning down to minimum seems to have rectified the false positives.

Thanks for the datasheet @ericgibbs. Surprising how such a ubiquitous module has such a poorly written datasheet. It says to expect an init time of 1 minute where the output can go high 3 times in this interval. I've haven't observed these low->high transitions from my module during start-up. Perhaps they've updated the firmware