HC-SR501 too sensitive

[g2c]

Hello, i am noticing that the new HC-SR501 pirs (from AliExpress) are much more sensitive and that is due to their lens: fitting old lens significantly reduces the senitivity. With the new pirs, cats at 3 meters can fire the pir even with the sensitivity pot set to 0 ohm, Any idea?

 

[schmitt trigger]

High sensitivity is actually good, as you can always partially mask/ shield the sensor. Some experimentation will be necessary.

On the other hand, if it had a lower than required sensitivity, you would be stuck with the sensor.

 

[tepalia02]

Have to tried to adjust the Two variable pots in the PCB?

 

[g2c]

High sensitivity is actually good, as you can always partially mask/ shield the sensor.

The modules spec says 3m to 7m human detection according to the pot setting (0 to 1M) now if at min sensitivity cats are detected than i face random # of false alarm. As for masking, what with? How to have consistent behaviour of 13 pirs around the house?. Some recommend a thin polyethylene sheet but I'm not sure how to have a consistent result: too small it may float, to large it may bend, hence different atténuation every time, every sensor.

 

[g2c]

Have to tried to adjust the Two variable pots in the PCB?

Yes, one pot sets the detection pw. I set it to min which gives ~3". The other sets tg6e senitivity, as said, with new lense, it's too sensitive even @0 ohm

 

[ZipZapOuch]

Or, you can buy a PIR costing more than 58¢ and with reasonably quality so it can be adjusted.

 

[Nigel Goodwin]

The modules spec says 3m to 7m human detection according to the pot setting (0 to 1M) now if at min sensitivity cats are detected than i face random # of false alarm. As for masking, what with? How to have consistent behaviour of 13 pirs around the house?. Some recommend a thin polyethylene sheet but I'm not sure how to have a consistent result: too small it may float, to large it may bend, hence different atténuation every time, every sensor.

Black insulation tape, many more 'professional' PIR's even give examples of where to apply it to restrict the detection angle - it's not a question of sensitivity, it's a question of masking out animals (such as cats) at below human levels.

Mind you, cats here sit on a flat roofed out-building, and wave their paws down in front of the PIR to add some light

Cleverer creatures than you think cats!.

 

[Nigel Goodwin]

Or, you can buy a PIR costing more than 58¢ and with reasonably quality so it can be adjusted.

The SR501 is already adjustable, it's the angle of detection that's the issue, not the sensitivity - presumably the new version simply has a better fresnal lens?.

 

[ZipZapOuch]

The SR501 is already adjustable, it's the angle of detection that's the issue, not the sensitivity - presumably the new version simply has a better fresnal lens?.

The op wants to detect a person but not a cat. Seems like a sensitivity adjustment knob would be better than adding a bad "lens." (Attenuator).

 

[Nigel Goodwin]

The op wants to detect a person but not a cat. Seems like a sensitivity adjustment knob would be better than adding a bad "lens." (Attenuator).

Presumably you've never used PIR's? - or read the instructions?.

Cats are low to the floor, people aren't - you want reduced coverage, not reduced range.

 

[g2c]

Nigel Goodwin - my PIRs are at ~3m heighr, on the wall and point dwnwards to a window at ~1.5m. Cats are at ~.2m height, man (center if irradiation) at ~1.3m I suppose that reducing the sensitivity is the solution. The old Fresnel worked jusr fine for years. Main difference - they are more 'milky' more opaque

 

[Nigel Goodwin]

Nigel Goodwin - my PIRs are at ~3m heighr, on the wall and point dwnwards to a window at ~1.5m. Cats are at ~.2m height, man (center if irradiation) at ~1.3m I suppose that reducing the sensitivity is the solution. The old Fresnel worked jusr fine for years. Main difference - they are more 'milky' more opaque

I would say not - the issue is almost certainly the angle of detection, and the new Fresnel lens presumably provides a different pattern of coverage. Obviously you don't want your PIR detecting along the ground, so either aim it up further, or blank off the respective part of the lens with insulation tape.

Have a look here, in particular the instruction PDF:

LUTRON Occupancy Ceiling PIR Masking Kit from Alltrade

www.alltrade.co.uk

 

[g2c]

Nigel Goodwin please look at the picture. Each of the three pirs, in the aluminium enclosure, point to "its" window

 

[Nigel Goodwin]

Are those pointing vertically downwards? - that would explain your issue, you're aiming at cats

 

[g2c]

Darling, with the old, more opaque lenses it worked perfectly well for years. Note the the alarm is set only if the total number of excitations per sliding time window exceeds a threshold.

 

[Nigel Goodwin]

Darling, with the old, more opaque lenses it worked perfectly well for years. Note the the alarm is set only if the total number of excitations per sliding time window exceeds a threshold.

Makes no difference, you're pointing the PIR's in completely the wrong direction, actually trying to detect cats - if they were aligned correctly you would get greater range, and avoid cats. Your issue 'may' be due to improvements in the SR501's, giving increased range.

There's a schematic here:

Dark and Motion Activated LED Lamp HC-SR501 LDR Triac Relay Mosfet – Electronics Projects Circuits

I will give information about how the HC-SR501 PIR motion sensor module works, HC-SR501 Features and its use with LDR. The HC-SR501 PIR sensor module can be use

320volt.com

So you should be able to reduce the gain by examining that.