HC-SR501 false detection during day with arduino Mega

Other Hardware Sensors
1

Dear community colleagues,

I am trying to add some security to my country house which had been burglarized more than once. I started by setting 3 HC-SR501 on the upper center of western outside wall, all three in a small rounded and waterproof plastic box in which I drilled 3 holes of the size of the senor's Fresnel lens, each sensor 'pointed' to one of the three windows of this wall. Indeed, this works pretty nicely and whenever a human moves by a given windows, the movement is detected by the corresponding sensor. Now, the data is collected by an arduino pin change interrupts (can have up to 18 sensors) and is logged to the Sparkfun data Phant site.

The problem is that during the day, the PIRs randomly fire more than every minutes. Yesterday, they fired ~500 times for 07:00 to 19:00 and zero times from 19:03 to 06:45.

And so i was wondering if someone could recommend a mean to reduce this false alarms rate, probably due to cloud movement sufficiently to to enable the system monitoring intruders even during the day

Thanks,

Guy

2

PIR sensors actually have two (or four) sensors that cancel out the background temperature, so it is really detecting the difference from the ambient temp. Because the thermal characteristics aren't perfect, as the ambient temp rises, the output voltage will rise a little also. You might want to try some code that 'zeros' the input voltage every 10 minutes or so, and then it can detect anything higher than 'zero'.

3

Thanks but the HC-SR501 module output a digital signal (to the best of my knowledge)

31227sc hc-sr501 (2).pdf (854 KB)