Hello friends,
I need to detect the presence and the absence of a person in front of a display. Traditional PIR sensors with prismatic lens are useful to detect motion, but if people are stationary they are invisible to it.
The range should not be very high, it's enough a distance of 1 meter or less.
Do you have any clue on how to do it? Can a PIR sensor like the Murata IRA-E700ST0 without lens work?
http://www.murata.com/catalog/s21e.pdf
Thanks
Ultrasound?
PING or SRFxx
Thank you Groove for the advice.
I found SRF02 sensor is perfect, it has also serial connection which is useful as I'd like also to wire it directly to a PC.
However it's a bit too expensive. Is there anything else I can try to detect a human body? I don't need precise distance measurement, just to know if it's in range or not.
I was thinking on a PIR detector like the Murata one that measure average IR light detected, then a comparator detect if the threshold is too low and outputs a low signal that can be read as a digital input.
Ultrasound? PING
A few things of interest from my attempt to detect a human using the Parallax PING...
Anothrt option if you want to detect someone that close to your display would be to put some kind of switch (or switches) under a mat or a piece of carpet.
Abit left field but you could combine PING and a Temperature sensor, I have a DS18S20 sitting on my desk connected to an arduino and LCD, they are super sensitive and just being within a meter of the sensor is enough to register a .5 - 1 degree C temperature rise.
When I walked into the room the sensor was 26.69 degrees and it's now 27.19
If cost wasn't a consideration I'd suggest a: Parallax MLX90614 non contact temp sensor. But they're pricey. Perhaps you could find a cheap hand held unit (I picked one up for about £20 a few years ago) and hack it up?
If you have access to the opposite side, how about a light gate? For example an IR led on the opposite wall, pointed at an IR sensor at the display.
Edit: when thinking it over again, this isn't great 
You dont know if people are standing close or far away, and the spread is way too limited probably.
I've been playing with one of these IR reflector sensors, works great and would be a simple solution for what you are looking for.
Lefty
I already have some DS18S20 sensor and already found they are influenced by nearby heat emissions, so it's a nice idea, however if you want to connect it to a PC it requires a 1-wire master like the DS9097U that costs around 14 euros.
For that price I could buy a ultrasonic SRF02 + MAX232 or similar chip, the module needs 4mA power and MAX220 0.5mA, probably I can power it directly from the port.
If I add a FTDI FT232R USB to RS232 chip the bill goes to 20 Euros just for the components, and it becomes to be harder to justify as a power saving solution
IR reflection would be much cheaper, unfortunately Seedstudio is located in HK and I'd prefer to buy in the EU because the custom is too slow.
Here I've found this interesting page
http://www.ikalogic.com/ir_prox_sensors.php
The SRF02 will also talk I2C, so no need for any MAX232. (In fact, the serial I/F is TTL, so no need for a MAX232 either way - which one it speaks is determined by a DC condition on one pin)
yes you're right AWOL, Arduino can handle I2C as well as serial TTL, but I was looking for a solution both portable (with an Arduino and a LCD display), and fixed (directly connected to a PC, right under the monitor)
I found an even better explaination on the same site of a IR emitter and detector more accurate even on ambient light, it uses the same technique for remote controllers
http://www.ikalogic.com/ir_prox_sensors_40khz.php
Close to a screen you say... a computer? With a webcam?
In that case you can detect the presence by comparing the pixels from the camera to a reference photo of the background.
J
You could use one of the Sharp Infrared Proximity Sensors from SparkFun Infrared - SparkFun Electronics.
Well, you might try using a modulated IR signal (aka a $5 universal tv remote control) and a modulated IR detector (Radio Shack). To test the theory, put an object infront of your IR controlled device (tv, etc) at your chosen distance, then stand behind the device and point the remote at the object and see if you can control the device. If this works, then you can do the same with your detector setup. You would use a tube lined with black absorbative material on the inside for both the IR emitter and receiver such that only reflections from the desired point would be detected.