I wanna make a body heat detector

[neferson]

if any one have anything please help me

 

[nettron1000]

Ever heard of night vision goggles or scopes ? Getting the parts to build one would be quite expensive.

 

[Russlk]

A cadmium sulphide (CDS) cell will respond to heat and light. You will need a lens to concentrate the heat and a sensitive amplifier.

 

[DigiTan]

Use a **broken link removed**.

 

[Oznog]

I'm not aware that the cadmium sulphide photocell has any ability to detect thermal infrareds, just visible light.

Thermal infrareds are lower energy than the infrareds of say a TV remote, and consequently harder to detect. It's not a matter of noise discrimination either- the photoelectric effect that all photodetectors are based on have an inherent lower threshhold. If a photon doesn't have the energy (its wavelength is too long) to trigger the effect, nothing happens no matter how many photons hit.

Thermal infrareds are also difficult to interpret. Everything above absolute zero, including the body of the sensor and lenses, emits their own infrareds. And the infrared of the environment often varies by orders of mangintude.

The PIR detectors do detect thermal infrareds, and deal with noise by only triggering when a sudden change in infrared occurs. Additionally, the funky milk-white lens in front creates "zones", the purpose being that a person walking in front will cause multiple rise/falls in the detection level rather than one when he enters the field of view and one when he leaves.

There's also thermal imaging, which has a video output and gives an entire picture. Much more complicated and expensive, but not nearly as expensive as it used to be.

 

[Oznog]

Oh, forgot to mention. There's also digital infrared thermometers, which of course give an absolute temp measurement. Still, to have any hope of detection you'd need a strong differential between the person and environment. With clothing, a person is only a few degrees or less above ambient, but ambient varies a lot more than that in many enviroments.

 

[Optikon]

I'm not aware that the cadmium sulphide photocell has any ability to detect thermal infrareds, just visible light.

Thermal infrareds are lower energy than the infrareds of say a TV remote, and consequently harder to detect. It's not a matter of noise discrimination either- the photoelectric effect that all photodetectors are based on have an inherent lower threshhold. If a photon doesn't have the energy (its wavelength is too long) to trigger the effect, nothing happens no matter how many photons hit.

Thermal infrareds are also difficult to interpret. Everything above absolute zero, including the body of the sensor and lenses, emits their own infrareds. And the infrared of the environment often varies by orders of mangintude.

The PIR detectors do detect thermal infrareds, and deal with noise by only triggering when a sudden change in infrared occurs. Additionally, the funky milk-white lens in front creates "zones", the purpose being that a person walking in front will cause multiple rise/falls in the detection level rather than one when he enters the field of view and one when he leaves.

There's also thermal imaging, which has a video output and gives an entire picture. Much more complicated and expensive, but not nearly as expensive as it used to be.

Have you considered fooling around with a CCD array? I've heard that some CCD's can pickup IR easily..I don't know but low end digital cameras these days are quite inexpensive IMHO if those would be sensitive enough..

 

[tansis]

Basic PYROLECTRIC sensor circuit
https://circuitos.tripod.cl/schem/r17.gif


Build an Infrared night scope, getting parts may be difficult..
**broken link removed**

Good description of how they work,two very usefull application circuits
https://www.electro-tech-online.com/custompdfs/2004/05/pirmanualPDF.pdf

 

[bmcculla]

The wavelength that your body emits is much longer than CCDs can detect.

The device I'd recommend is called a thermopile. Thermopiles are tiny thermocouples made from silicon that are heated by long wavelengths of IR. Digikey sells some made by melexis for about 12 dollars.

Something else you can look into are those motion detectors used in automatic lighting and security systems. The problem whit these is that they are AC coupled devices. this means that they can only detect changes in temp not absolute temperature. The sensor is called a pyroelectric. Some systems use a chopper wheel that gets constanty causes changes in input to allow DC measurements.

Hope this helps
Brent

 

[bmcculla]

Another comment: nettron1000, those night vision goggles you are talking about actualy use a totally different technology than infrared cameras. They use an amplification system that is like a photomultiplier tube to detect visible and short wave infrared. The technologiy fabricates many mini photo multiplier channels into a plate so the incomming light is amplified and produces an image. Photo multiplier tubes are very sensitive: they can detect single photons so this system can make an image even in very low light.