Hi! I'm considering to buy an Arduino+PIR+servo to build a roach trap.
PIRs seem designed to detect "biggie" objects like a person, and datasheet says working distance is 3-5 meters. I assume that's the maximum range. What about the minimum?
In short, will a PIR detect a small roach (say 1 cm long) passing in front of a PIR at 5-10 cm distance?
If not, any other (cheapish) sensor to use?
Thanks!
"Hottie" like a person. IR radiating from the object triggers the Pyroelectric InfraRed sensor. I would guess bugs have little emissivity.
If PIR does not work, try doppler.
Roaches, like most insects, are generally "cold blooded", at nearly room temperature, and almost invisible to PIR.
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Insect detection is done using ultrasonic microphones. They rub their body parts to make sound. No standard frequency for security reasons!
Thanks folks!
I will check the ultrasonic and doppler sensors, hopefully they work with small objects (and with low speed)...
Even an ACTIVE IR could be an alternative, I could design the trap so the roach is forced to pass through a narrow passage to reach the food.
I am am an electronic security & surveillance field engineer (49 years) with extensive background & expertise in all types of motion sensors and space protection devices such as
microwave, ultrasonics & Passive Infra-Red (PIR) and the answer is NO, the theory behind it is that a PIR looks for multiple factors (this helps eliminate false alarms/triggers) these are a change of temperature in it's field of view in relation to the environmental background along with passing thru multiple lines of focus (consider it to be like spreading your fingers apart with you palm down fingers pointing forward) and the temperature change would need to register in multiple zones in that field of view...
So insects are not large enough or have the temperatures necessary to be picked up as insects are cold blooded.
To note that does not apply to ultrasonic or microwave sensors as they work on the 'Doppler Effect' created by a mass moving thru the foeld in their 'view' and just a side note that these type of sensors would also ignore the insects because they lack the mass necessary to create the Doppler Effect based on the sensitivity of the sensor which is adjustable but but not for small thing such as a roach (unless the sensitivity it cranked all the way up and the insect gets inside and actually crawls across the transducer or the antenna)
Just a little thing: the RCWL-0156 is not doppler, is not radar. That sounds fancy but is total BS.
What it does do, is measuring interference/reflections to its own microwave signal (around 6 GHz I recall), and changes in that (caused by motion of objects in its range). That also explains why those sensors tend to not work out in the open: nothing around to create a baseline interference.
They do work great, though!
That is what Doppler and RADAR do. Show echos and possibly detect anomalies.
Doppler measures changes in frequency to determine speed.
Radar looks for actual reflections and directions.
The RCWL-0156 sensing has no idea on speed of movement, direction of where the movement is. It's much closer to PIR for that matter than radar or doppler shift sensing.
Except that they measure reflections from the object, not changes in the interference pattern generated by reflections from the object plus surroundings.
@wvmarle is correct, the microwave sensors don't work well or at all outdoors. See https://www.rogerclark.net/investigating-a-rcwl-9196-rcwl-0516-radar-motion-detector-modules/comment-page-1/
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