how can i detect the presence of people in a room... need it for automation.. any help is appreciated!? Answered


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need an idea to detect the presence of somebody in a room, and if no one is present cut off the power supply in order to save power, what sensors can be used? and is it possible?

thank you...



Best Answer 8 years ago

Besides the PIR sensors (used as "motion detectors" in alarm systems and some automatic doors), and asking people to wear a tracking tag, and using weight-sensitive floor mats (also used in alarms and door control) there's also the option of setting up a pair of photocell beams across the doorway -- two so the sequence in which the beams are broken lets you determine whether someone was moving into or out of the room. Advantage is that, like the tags, it lets you actually count how many people are in the room; it also doesn't need motion to "keep it alive" as the PIR sensors do -- and it's easier to cat-proof.. Disadvantage is that there are some scenarios where it may lose count, though that's easy to reset.

(The floor mats might have problem if you left a box in the room, or moved furniture around, come to think of it. Though I *have* seen that approach used in a research lab.)

Another approach would be video and image analysis. But again, allowing for varying lighting and the like would mean that this might tend to lose people who are sitting still for a long time.

PIR is used in some commercial office-lighting systems, for what that's worth. Though I *have* had that turn the lights off with me still in the room, after I've been sitting near-motionless too long (reading, or at a keyboard).

The ideal -- though more expensive -- solution might be to combine several of these and have them "vote" on whether someone is still present or not.


2 years ago

i have tested many method that was mention bellow by YS PAI all method have many flaw what about in case of when cat , rat or dog present in room our circuit will assume as men or and keeps light on


8 years ago

lol! Bill Gates has exactly this kind of thing in his house, if you believe the hype. Apparently, everybody wears this RFID tag and huge plasma screens change their decor to suit your requirments, heating, lighting and so on. We know it's failed several times because it (used) to be controlled by Windoze servers but it seems as though he switched to Linux! Believe what you will....(!)

In short, there are any number of technologies you might employ in order to detect people and then control the power. If you wish to power totally down - my immeidate thoughts are to use any preferred sensor to control a relay which can then either allow or shut down power to the whole room or the bits you wish to control.

In any scenario, you might wish to clarify whether you need an MCB fault-circuit tripper after the relay to maintain protection. I'm really not sure about this point but I'd rather look stupid and ask the question anyway and get to keep living. ;-)

ys pai

6 years ago

Use Binary sensors- Contact sensors, Breakbeams, PIRs, Ultrasound motion sensors
Pressure sensors- Piezo-resistors, Piezo-electric materials
Chemosensors- CO2 sensors, Humidity sensors
Doppler-shift sensors- Radios, Ultrasound transducers
Photodetectors- Phototransistors, Photodiodes
Cameras CMOS- image sensors, CCD image sensors, Specialized motion- or
edge-detecting imagers
Thermal- imagers Microbolometer arrays, PVDF (Polyvinylidene Fluoride) arrays
Ranging sensors- Ultrasonic range-nders
Scanning range sensors- Radars, Ladars, Sonars
Tomographic sensors- Radio pairs
Electric eld sensors -Capacitors
Inertial sensors- Accelerometers, Gyroscopes, Magnetometers
Vibration sensors- Seismic sensors, Accelerometers, Piezoelectric sensors, Electrostatic
microphones, Laser microphones
Motion sensors- PIRs, Motion cameras, Binary Doppler-shift sensors
ID sensors RFID, plus any communication system
Envir. recog. sensors WiFi ngerprinting, Wearable microphones, Wearable cameras


8 years ago

Most people use PIR sensors - they work, are cheap and reliable - provided people are moving !



Answer 8 years ago

These systems can be very frustrating for people who typically work at one workstation for extended periods. You'll want to avoid turning out the lights on someone who is there but not moving around. I once worked at a new lab that drove the staff insane by shutting off the lights on anyone who was not up & dancing in the middle of the room every 15 minutes.

When you pick a product to hack, check the Amazon reviews to see if the sensor performs as advertised. I bought a porch light that had a motion sensor built in but it never worked at all, so I don't know which manufacturers have good reliability.


Answer 8 years ago

+1 (and the sensors are positioned correctly...I had a friend who bought one of the automatic switches for the lights but had the sensor poorly positioned so it only registered about half the time)


8 years ago

Oh, I forgot, you may also need to consider whether your switching circuit makes for "dirty" voltages which might spike and/or surge your sensitive kit into oblivion. Sometimes a 'soft' start and finish are preferable.