How come all my three PIRs are always on?
Because all of them are bad guys.
Try the smallest guys below. They are very good.
You might like to show your PIR and a schematic, like below.
You might also like to study the datasheet and make a summary for troubleshooting reference.
More details are in Appendix A. You need to know more details when testing and troubleshooting.
You might notice that the datasheet does not give the output voltage values for motion detect and motion not detected. What are given are current values IOH, IOL +-10mA, and corresponding VOH, VOL values (Yes, you need a have a basic idea of IOH, IOL, VOH, VOL). The reason is that PIRs are often placed far far away from Rpi, so outputting currents through a long wire, perhaps 20 meters, and causes a DC voltage drop across a resistance (Note 1) near the Rpi is the usual trick for the PIR application.
If you don't have installed this current sensing resistor, you might have fake positives, I mean High signal, for ever.
I forgot to tell you how to check out the always High PIRs are bad guys. The trick is to use a rice bowl to cover up the bad guy. If the bad guy still says something is moving, of course he is lying.
(1) Introduction to HC-SR501 A complete step by step tutorial on Introduction to HC-SR501
(2) TaoBao HC-SR501 PIR Sensor Module - ¥3.23
(3) TaoBao DC 12V Water Proof Smart PIR Sensor Module With Switch - ¥12.80
(4) TaoBao AM312 PIR Sensor ¥5.28
(5) AliExpress AM312 DC 2.7 to 12V Mini IR Pyroelectric Infrared PIR Motion Human Sensor Automatic Detector Module - US$1.29
(6) Pyroelectric Infrared Radial Sensor AM312 (DSP, Schmidtt) Manual - NanYang SenBa
(7) PIR Sensor Description and Technical Details - AdaFruit
(8) PIR Sensor Tutorial - AdaFruit
(9) PIR Human Motion Module 10*8mm 2S delay time SB00322A-1 - Nanyang Senba Optical And Electronic, China
(10) SB312 Passive Infrared Sensor Module for Home Security System
(11) SB612 Human Motion Detector for Smart Toys From Senba Manufacturer
(12) SB412 High Sensitivity Digital PIR Modlue for Light Control Lamp
(14) Nanyang Senba Optical And Electronic Co., LtdNanyang Senba Optical And Electronic Co., Ltd
(15) How to use HC-SR501 PIR Motion Sensor with Arduino - Benne de Bakker, Maker Guides 2020Jan
(16) HC-SR501 PIR Motion Detect Producat Description
(17) BISS0001 Micro Power PIR Motion Detector IC Datasheet
(18) IR Parts Manual RE200B FL65 S211FL - GloLab
(19) Amazon Panasonic Plastic Pir Sensor (EKMC1603111, 3V~6VDC power, 12m detection range, digital output) - HK$110
(20) Panasonic PIR EKMC1603111, 102°, 12m, 3~6V
enter link description here
(22) HX711 Weigh Scale 1/3
(23) HX711 Weigh Scale 2/3
(24) HX711 Weigh Scale 3/3
(25) Motion - Wikipedia
(27) AlliExpress KonLen PIR motion detector 12V, 110 degrees Detection angle - US$10~40
(28) KeyStone KTS-PIR1-12V-AUX SMART PORT LED PASSIVE INFRARED (PIR) OCCUPANCY SENSOR (0~10V, 20mA Output) - US$30
Appendix A - Pyroelectric Infrared Radial Sensor AM312 Specification
Working voltage: DC 2.7-12V;
Delay time: 2 seconds;
Blocking time: 2 seconds;
Triggering method: repeatable
Sensing range: ≤ 100 degrees cone angle, 3-5 meters; (according to the specific lens)
Operating temperature: -20 - +60 °
Anti-interference enhancement, the internal use of digital signal
processing, direct high-low output.
Repeatable triggering mode: If a cat moves in the sensing range during the
delay period, and output is high, output will remain high
until delay time after the cast has left, ie, the sensing module will
automatically delay after detecting an activity of the cat, with the
time of the last activity as the starting point of the delay time.
Appendix B - SB312 Passive Infrared Sensor Module for Home Security System
SB312 Passive Infrared Sensor Module for Home Security System
New Smart PIR Sensor Module with improved digital sensor.
This unit has enhanced delay time adjustments, with an expanded range from 2 seconds to 70 minutes. The unit includes an integral light sensor with adjustable sensitivity, the unit is suitable for outdoor and indoor mounting. Detecting length is also adjustable. The output is a standard TTL output signal, that can be used with a microcontroller or for switching lights, etc.
(B1) PIR Human Motion Module 10*8mm 2S delay time SB00322A-1 - Nanyang Senba Optical And Electronic, China
(B2) SB312 Passive Infrared Sensor Module for Home Security System
(B3) SB612 Human Motion Detector for Smart Toys From Senba Manufacturer
(B4) SB412 High Sensitivity Digital PIR Modlue for Light Control Lamp
(B6) Nanyang Senba Optical And Electronic Co., LtdNanyang Senba Optical And Electronic Co., Ltd
Appendix C - AM312 Application Schematic
Appendix D - AM312 Setup
This PIR sensor is "plug and play". This is no adjustments necessary. Just power and sensor is automatically set up, in two seconds.
Appendix E - HC-SR501 Adjustment Cheat Sheet