Thanks, Bob. I haven't any practical knowledge about these sensors, just curious to find for PIR a possible aid in my "research". As I said in a previous mail, probably the better solution is observing the interest area at distance with a thermal IR camera but the price is still high for me. Also IR Thermometers seemed attractive (price is much lower) but I think it is very difficult using them for this scope. About twenty years ago I had on loan from my office "boss" an Minolta Cyclops IR thermometer that we was using for motherboard thermal analysis (very nice unit)! But testing it at 2-300mt of distance as "cave finder" wasn't satisfactory: very difficult to understand temp. values on the display, always oscillating for every smallest movement of the thermometer. The only good job was observing relatively big entrances of caves placed on the opposite wall of a canyon: the spot lens was able to circumscribe the entire entrance and I was able to know which of them was colder of the others. regards, Marco ----- Original Message ----- From: "Bob Axtell" To: "Microcontroller discussion list - Public." Sent: Thursday, April 16, 2009 12:14 AM Subject: Re: [EE]: Temperature detection with a PIR sensor I have spent time tinkering with these things, too. Low frequency IR sensors sense MOTION, not temperature, by detecting differences between two detector segments inside the PIR sensor. I doubt that it can be made to detect absolute temperature. People and animals are detected when they block a colder or warmer background by moving in front of it. Very sensitive sensors can detect a blockage when a person or animal blocks emissions from the "Big Bang". In general, these things are not very effective. A better detector of persons at a distance can be made by studying video camera pixels, then applying a detection algorithm. But it draws a LOT more current than a PIR device. --Bob A On Wed, Apr 15, 2009 at 2:14 PM, Marco Genovesi wrote: > Vasile, > sorry for this very late reply but I have been out of home for some days. > In > one of these I have tested > my portable PIR led lamp directly in the field, that is a small karst hill > where I know some cave entrances. > Weather was fine in these days, so at 14:00 h. from two of these a cold > (about 9 C.) airflow exited. > Passing overe the entrance, the PIR sensor easily trigger on, but walking > along the terrain it frequantly triggers > also when apparently there isn't an entrance or an airflow due to a cave: > it > probably happens when passing over sunny > rocks or in shadow. Practically, in outdoor it seems too sensitive or has > false triggering.... > > Maybe it is possible to do some modifications to the internal circuit (it > isn't an smd layout) to reduce the sensitivity > but I'm guessing if this is the right solution for my necessities. How was > your "layout" and why there was the chopper? > (if the PIR sensor is a two-elements I think it is not necessary, right?). > > ps: many thanks to all for the replies > > Marco > > > > > ----- Original Message ----- > From: "Vasile Surducan" > To: "Microcontroller discussion list - Public." > Sent: Wednesday, April 08, 2009 1:18 PM > Subject: Re: [EE]: Temperature detection with a PIR sensor > > >> Hi Marco, >> >> I've built a termometer with a PIR about 10 years ago. I was able to >> sense a difference of temperature of 1C into a cup of tea at 40C. >> Warm the tea at 40C, then put some cold water inside and mix untill >> the whole cup content go down to 39C. >> Do you want a picture of it? I guess is somewhere on my lab. >> >> As I told you, you need a chopper to modulate the thermal radiation. >> Then everything is much sensitive than you can imagine. >> >> Vasile >> >> On 4/3/09, Marco Genovesi wrote: >>> >>> 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 >>> >> -- >> 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 -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist