— Work in Progress —

I am evaluating range, sensitivity, immunity from false triggering, and power requirements, for various projects around the house. In particular, I would like to be notified when a person or a vehicle comes down my driveway, so I can light the way if it’s dark.

Sensors Considered

1. Passive Infrared (PIR)
   1. AM312 3.3 or 5V, active low
   2. SB0072 Futurelec MINI_PIR_MOD_B 5-20V, adjustable delay time
2. Microwave Doppler
   1. RCWL-0516
   2. RCWL-9192
3. Ultrasonic (SONAR)
   1. RCWL-1655 board and waterproof ultrasonic distance sensor

TLDR;

PIR produces many false triggers with sunlight and moving foliage.

Microwave Doppler is pretty short-range

Ultrasonic is pretty short-range

Testing

Passive Infrared (PIR)

Microwave Doppler

Ultrasonic (SONAR) – RCWL-1655

Range: Quoted as up to 5 meters; detects humans up to about 1.5 meters

Immunity from false triggering: Once I filtered out zero-responses, I only see false triggering when there is a target too small or too far away to reliably register.

Power requirements: Currently testing with a 1500 mAh LiPo battery; started the test on 2024-09-22 at 21:00 or so.

Test routine:

• take a reading “ping”
• if result is different than before, take repeated readings until two in a row match within 10%
• if this new “clean” reading is different than before, report it with a JSON message transmitted via LoRa
• sleep for 0.25 seconds (originally 1 second). Since the processing takes 120ms or so, sleeping for 250ms cuts power consumption by perhaps two thirds.