Post by thread:Detecting temperature at a point

In message <spam_OUT9511280206.aa02498TakeThisOuTpunt-4.mail.demon.net> .....PICLISTKILLspam@spam@MITVMA.MIT.EDU writes: > I'm trying to use the PIC processors to detect temperature at a point. > Unlike area or room thermometers, I want to take the temperature a spefic > point (eg. water or body temperature). Would anyone know of any sensors > that would be suited for this? I have thought of themiresistors and > temperature ICs. Are there anymore or better ones? If not, which is better? > Thanks in advance. > Hi, You could try the Dallas Semiconductor DS1820 - a 3 lead device that does the temp -> digital conversion for you. It uses just one i/o pin for communication, requires no external components and measures temperatures in the range -55 degC to +125 degC in 0.5 degC increments. It also has under and over temperature alarms. Hope this helps, Mike Watson -- Mayes uk

----- Begin Included Message ----- From: Gerry Smith <LIUKBKILLspamKIRK.NORTHERNC.ON.CA> Subject: Detecting temperature at a point I'm trying to use the PIC processors to detect temperature at a point. Unlike area or room thermometers, I want to take the temperature a spefic point (eg. water or body temperature). Would anyone know of any sensors that would be suited for this? I have thought of themiresistors and temperature ICs. Are there anymore or better ones? If not, which is better? Thanks in advance. ----- End Included Message ----- The devices you mentioned really only take temps at the point where the sensor is, not of an area. You might try attaching your device directly to the object you want to monitor, and insulate from heat coming from other directions to get better readings. If there are more (cheap?) sensors, I am sure several of us are interested!

---------- {Quote hidden}>In message <.....9511280206.aa02498KILLspam.....punt-4.mail.demon.net> EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU > writes: >> I'm trying to use the PIC processors to detect temperature at a point. >> Unlike area or room thermometers, I want to take the temperature a spefic >> point (eg. water or body temperature). Would anyone know of any sensors >> that would be suited for this? I have thought of themiresistors and >> temperature ICs. Are there anymore or better ones? If not, which is better? >> Thanks in advance. >> >Hi, > >You could try the Dallas Semiconductor DS1820 - a 3 lead device >that does the temp -> digital conversion for you. > >It uses just one i/o pin for communication, requires no external >components and measures temperatures in the range -55 degC to >+125 degC in 0.5 degC increments. It also has under and over >temperature alarms. > >Hope this helps, > >Mike Watson >-- >Mayes uk > The DS1620 (available from Jamco for $7.00 US) is also available with a rhree wire communicationa line. I have played with a cheep thermister that I hooked up to a 555 ic. I hooked the thermister in the "charging" circuit of a 555 and put a diode in series with it so that it will have no effect on the discharge time. Then I used the pc to count the on time and off time of the 555 output (in the free runing mode). The tempreture measument is made by taking the ratio of the "on" time to the "off" time. This can be used to determin very small changes in tempreture. Because of not being in sync with the 555 and the various interupts on the pc, the counts do vary. But averaging a few of the counts will smooth out the reading (and slow the sampling rate). In the PIC books there is an example of using some i/o pins to read a variable resistor (which is what a thermister is). I do not remember how it is used exactly, but here is a susgestion. The series circuit consists of three componets. The thermister, a resistor (to limit current through PIC pins) and a capicator. The other end of the capicator is connected to ground. The other end of the thermistor is connected to a pic i/o pin. A second PIC i/o pin is connected to the junction of the thermister/resistor. The circuit works by charging the capacator through the thermister and measuring the time, then discharging the capacator, and doing it again. The cap is discharged by tristating the i/o pin hooked to the thermister and outputting a low (ground) on the pin hooked to the thermister/resistor junction for a good length of time. Then to start the reading, the junction pin is set to input and the thermister pin is set to output a high (+5v). Now the cap is charging through the thermister. A count of the time it takes for the voltage on the junction pin to raise to the point where it is read as a high input by the PIC. This time is the tempreature. Just be sure you have the resistor in the circuit to limit any current (assuming 5v) to a safe level for the PIC pins. To get more fancy, could you use a ir device? A ir transistor? Would it go in one of the above circuits as a current device? Or could it be hooked up to the control pin of a free running 555 to change frequency of the 555's output. Then you could just point the device at something and get its tempreature. If you use some crazy scheme to measure tempreture, it may be wise to also get a Dallas Semiconductor device that is calibrated and use it to reference the readings of your device. Take some salt or cooking oul and heat it in the micro wave. Then stick both devices in the stuff and have the computer record the readings from each as it cools to room tempreature, Then put the stuff in the freezer for a while and repeat the reacordings as it warms to room tempreature. Then you will have a good conversion table. Bill C.

Gerry Smith <LIUKBspam_OUTKIRK.NORTHERNC.ON.CA> wrote: > I'm trying to use the PIC processors to detect temperature at a > point. Unlike area or room thermometers, I want to take the > temperature a spefic point (eg. water or body temperature). Would > anyone know of any sensors that would be suited for this? It sounds as though you want to measure temperature at a distance. Is that true? If so, there are plenty of manufacturers of infrared pyrometers that'll do exactly what you want. I had one about 8 years ago that would display a person's skin temperature from across the room... They're real cool. I don't know, offhand, who makes the sensors; you may want to try calling Omega Engineering at 800 826-6342. They make a whole line of infrared thermometers and can probably give you some information about the raw sensors. -Andy Andrew Warren - @spam@fastfwdKILLspamix.netcom.com Fast Forward Engineering, Vista, California http://www.geopages.com/SiliconValley/2499

Eltec Instrment, Inc. (1-800-874-7780) makes pyroelectric detectors and I agree they are really cool! I have been researching them for use in home robotics to differeniate humans from other inanimate objects. I've been writing a research paper for one of my classes that I will probably put on my WEB page in a couple weeks if anyone is interested. Ben Ben Wirz Check out My Home Page for Great Deals on Bulk Buy Electronics (LMD 18200 H Bridge and PIC 16C84) KILLspamblw2KILLspamcec.wustl.edu http://cec.wustl.edu/~blw2/index.html On Tue, 28 Nov 1995, Andrew Warren wrote: {Quote hidden}> Gerry Smith <RemoveMELIUKBTakeThisOuTKIRK.NORTHERNC.ON.CA> wrote: > > > I'm trying to use the PIC processors to detect temperature at a > > point. Unlike area or room thermometers, I want to take the > > temperature a spefic point (eg. water or body temperature). Would > > anyone know of any sensors that would be suited for this? > > It sounds as though you want to measure temperature at a distance. > Is that true? If so, there are plenty of manufacturers of infrared > pyrometers that'll do exactly what you want. I had one about 8 years > ago that would display a person's skin temperature from across the > room... They're real cool. > > I don't know, offhand, who makes the sensors; you may want to try > calling Omega Engineering at 800 826-6342. They make a whole line of > infrared thermometers and can probably give you some information > about the raw sensors. > > -Andy > > Andrew Warren - spamBeGonefastfwdspamBeGoneix.netcom.com > Fast Forward Engineering, Vista, California > http://www.geopages.com/SiliconValley/2499 >