On Sat, 19 May 2007 01:10:44 -0400, you wrote:

>Hi all,
>
>The IR emitted by IR LEDs in remote controls, etc., is just slightly
>longer than visible light (shorter than 1 micron wavelength). The IR
>emitted by hot objects in the 100 deg C range is going to peak around
>several microns in wavelength, way too long for a regular CCD to see.
>The problem is not that the emission is weak but that it is the wrong
>wavelength.
>
>Vitaliy, I don't know what your friend was able to see on the PCB with
>a regular camera in "night mode" (which is usually just removing the
>IR filter and illuminating with IR LEDs).
>
>IR thermal imaging cameras use exotic focal plane array detectors
>(made not from Silicon or GaAs, etc. but from InCdTe, InSb, PbS, or
>similar materials, or microbolometers which are arrays of sensitive
>temperature sensors which absorb the incident IR and measure the
>resulting tiny temperature increase). I don't think you are going to
>find them for anything less than several thousand dollars new. You
>might possibly find something used on eBay for much less. A quick eBay
>search turned up a few hits in the low thousands of USD. The
>technology is the same as used in newer generation heat seeking
>missiles.
>
>Sean

The only 'really cheap' thermal detector is an IR thermometer.
A while ago I hooked up one of the detectors used in these to an oscillator +speaker to give fast
feedback when scanning the detector over a PCB- never had time to develop this further, but with the
right optics (very few materials suitable for this - IR thermos tend to use moulded polythene
fresnel optics) this may be a viable solution as the audio makes it  very quick to home in to
hotspots.

If you want a 'real' thermal imager, the cheapest solution I know of is a people counter made by
www.irisys.com. This has a 16x16 array, and can produce images on a PC, however you would need to
tweak the optics to work at the required distance. Cost is around GBP700 (~USD1400).
Note that as this doesn't have a chopper, it only reacts to changes in temperature.  

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