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I saw this fictitious product on the web and was impressed: http://www.behance.net/gallery/Sprout-Infant-Monitor-System/4033245 However, as I said the product does not really exist, but the seed is planted and I seek to find a means to achieve something similar in the DIY fashion.

At the moment I'm only interested in the temperature reading from a distance feature. I've run into a bit of a problem identifying a temperature sensor that is capable of taking a reading from any range more than 10cm. I've scoured the Googles and found the most popular sensor was the MLX90614, but that is extremely short range from what I gather. I was searching for any long range temperature sensor compatible with the Arduino, but only found a few that had extremely limited range.

There are other important factors such as precision, effective angle, and operating condition limits, but they are all less of importance behind effective range.

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  • \$\begingroup\$ Take a look at Panasonic Grid-Eye sensors (8x8 matrix of temperature sensors with I2C). If you are in the US of A or in Japan you might even be able to get them (Digikey won't ship to Europe citing export regulations). \$\endgroup\$
    – starblue
    Commented Dec 6, 2012 at 19:34
  • \$\begingroup\$ The Grid-Eye looks like a very viable solution that would cover both temperature and movement detection. I'm going to explore this option. \$\endgroup\$
    – Sn3akyP3t3
    Commented Dec 7, 2012 at 16:03

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The MLX90614 actually can work over large distances. Since it is an infrared sensor, it detects the radiation from the object you want to measure, and this does not really change with the distance. The limiting factor for the distance is the angle which the sensor covers. When you look at the data sheet you see that the sensor comes in different variants, from 90 degree down to 10 degree sensor angle. The sensor is most accurate when the object to measure fully covers its field-of-view. For the 10 degree version, the object should be larger than 17cm (at a distance of 1m). If it is smaller, the sensor will report the average temperature of what it sees.

Another option would be the TMP006 from TI, which has an I2C interface. But since it has a larger FOV (nearly 180 degree), at a distance of 1m the object should have a diameter of about 4m. Nonetheless, the TMP006 userguide makes a good read, since it explains the basic of infrared measurements, and all the calculation much better than the Melexis data sheet.

One thing to note, though, is that IR sensors will measure the skin temperature, which can vary significantly from the body temperature.

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Your best (and really the only easy available option) is a thermal camera.

However, you need to be aware that they are several thousand dollars for the cheapest models available, and it won't completely solve your problem. You will need to add some sort of image analysis on top to determine where the child is in the frame. Also, clothes and body position will affect your measurement.

Also, surface body temperature is both fairly dependent on the atmospheric temperature, and not a direct representation of actual core body temperature. The way the "forehead" thermometers actually work is the measure skin temperature, and feed that through a complex lookup table that is derived from measuring both actual core body temperature and skin temperature of thousands of people, and computing the statistical mean relationship.

Really, you should just use a wrist-strap or a collar assembly.

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