Hello Vasile, as I said to Jinx in the last e-mail, I was going to buy a PIR detector for some tests. Oh, a bit "poor-man" detector... but eventually good for lighting the income of my house that is always in the shadow-dark. These are the specs: case: plastic, approx. 8x6x3 cm light: n. 4 white leds wide angle power: 4.5V (n. 3 AA cells). PIR sensor with half-spherical fresnel lens Angle and distace of detection: 100 degree - 5meters There is also a 3-positions switch (on-off-auto) and a CDS cell that don't fire the leds if the lux level is enough. 1) Hair dryer test1: In the dark - with an hair-dryer lateral to the PIR, I have directed the (very) warm air in front of the sensor (distance 40 cm) moving it rapidlly up and down. Result: NEGATIVE (mmm... Olin is right here... seem that air don't has a valid IR emission!) 2) Hair dryer test 2: in the dark - hair-dryer was off, but his platic cap was still hot. As soon as the cap pass in the PIR detection range, the leds are illuminated (WOW..OK!) 3) Test refrigerator: with slightly opened door (few centimeters), when I move the PIR accross the door, the leds are illuminated (OK). 4) Yoghourt Test (!): in the dark - get the yoghout bottle on the kitchen table. When I move the PIR along the table (1 meter distance) and I cross the yoghout, the PIR starts the leds (OKK!) And so on... Practically, moving the PIR over objects with different temperature, get the leds on. Apparently, seems there isn't difference if the object is cold and the surrounding ambient is warm or reverse: the PIR notice this and works. If this is right, my original scope may be still possible: the cold air exiting from a cave entrance isn't sensed but instead is sensed the rock cooled from the air (and the result is the same for me). Well, next week I think to do some tests but in the field, with really blowholes and caves. Thanks a lot who has given suggestions and patience! Marco ----- Original Message ----- From: "Vasile Surducan" To: "Microcontroller discussion list - Public." Sent: Thursday, April 02, 2009 1:01 PM Subject: Re: [EE]: Temperature detection with a PIR sensor > Yes, of course. You need a mechanical (or optoelectronical) chopper in > front of your PIR detector. > > On 4/1/09, Marco Genovesi wrote: >> >> Maybe simple but I haven't any experience of this.. >> Is it possible to use a common PIR surveillance sensor to detect a >> warm->cold->warm temperature transition? >> I know taht the "normal" use in surveillance is to detect an "hot" body >> crossing the sensor area. >> Instead, I would to detect a cold "object" ( 15-20 C. less than the >> ambient temperature). >> A possible complication is that the cold "object" isn't a solid but >> really a localized flux of COLD air that rapidly >> cross the sensor area and that may be very near ( from 5 to 1 feet from >> the PIR). >> A real case: ambient temperature 25-30 C. and a cold air flux of 5-10 C. >> >> >> thanks, >> Marco >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist