I’m building a small hobby robot, and part of its mission is to detect people. It is my understanding that humans emit a certain wavelength of infrared light that can be used with some reliability to detect them- this is the principle on which the SE-10 Passive Infrared Detector is based.
However, I have several questions-
First, the Pololu product page for the SE-10 states that it detects infrared light on the 7 to 14 μm range because humans emit 8 to 14 μm. The data sheet on the other hand seems to indicate that it detects on the 7 to 14 mm range, because humans emit on 8 to 14 mm. There is a rather large difference between 8 μm and 8 mm. Which figure is correct?
Second, is there a way to get an infrared detector that just detects light- similar to a photo resistor- on a specific light range, in this instance, 7 to 14 μm/mm? The SE-10 detects changes in detected light and creates an alarm signal based on this- but it seems that if I had access to a raw 7-14 μm/mm detector I could use the scanning action of a turret to somewhat reliably detect people even if they are not moving or are moving towards my robot. I have seen plenty of IR detectors, but none that cater to a specific light range.
Of course if there is any other suggested way of detecting humans, please tell me. Thank you!
I think that the datasheet is incorrect or the result of poor character encoding when generating the PDF. If you use the equation from the Wein’s displacement law page, you will find that the 8-14 μm wavelengths corresponds to black body temperatures of -60 °C to 140 °C. The 8 to 14 mm wavelengths corresponds to about -272 °C (close to absolute zero). Here is another Wikipedia section that calculates the approximate wavelength that human’s emit using the displacement law.
Of course there must be detectors at this range because there are two of them inside the SE-10. I just don’t know how available they are as a component. I don’t know of a great solution for human detection in general. It might be possible to use the SE-10 as part of a turret, but I haven’t tried it myself. We also sell the MLX90614ESF-AAA infrared temperature sensor 90° FOV, but it would only work if your targets were very close to the sensor.
Thank you for the answer! That temperature sensor seems to be just what I was looking for. I had read a whitepaper about using a infrared thermal camera to detect humans (specifically disaster victims)… I should have realized that the “one pixel camera” I was theorizing about would just be a temperature sensor- after all, who needs a $500 640x480 camera when you have servos to manually scan?
I noticed that there are several more variants of the MLX90614ESF-*** part, two of which provide smaller fields of view, and I think one of those will serve my purpose quite nicely. Just for clarification, however, these sensors do take temperatures of objects (the average temperature of the field of view) a distance- so the 10 degree field of view sensor will take the average of an approximately 1’ diameter field 6’ away, correct? That is, they don’t just measure the temperature of whatever is within an inch or two of them- in the case of my proposed application, that would be a bit of air.
Can you tell us what $500 camera you’re talking about? The thermal cameras I’ve seen were more like $5k for 120x120 or so pixels.
Your understanding of the Melexis sensor sounds correct.
Thank you for the help.
The paper I read was this diploma work from Carnegie Mellon, and the camera referenced was the “Raytheon Infrared IR camera 2000b,” shown on page 16 of the above.
Apologies, I seem to have been an order of magnitude off, the first google hit was American Infrared, and the lowest search filter option on their site is $4,000-$11,000, not $400-$1,100 as I misread it
Then again for me, there isn’t that much of a difference between $500 and $5,000, both are far more than I can afford!
Also for anyone who is looking for the same thing as I am, it turns out Parallax offers a reasonably priced module with the 10 degree FOD version of the Melexis sensor.