IR Temperature Sensor

I am attempting to construct a temperature sensor that will activate several relays when the thermometer senses temperatures above 150 degrees Celsius, or ignition point for decayed wood. Unfortunately I have only been able to find this plan online, which has far more features than I need.

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If anyone knows of a circuit diagram that would be more to my needs or has suggestions of any sort, I would be extremely grateful. If you have any questions feel free to email me at snipped-for-privacy@yahoo.com.

Reply to
tranerm
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What do you mean by "IR temperature sensor"?

JF
Reply to
John Fields

By IR sensor I mean like the kind you can find in a computer mouse or motion detector, that can detect infrared energy (heat) and change the resistance based on this (I think that is how they work, anyway). I am trying to build a circuit where once the sensor is giving the correct signal back, a relay will be tripped, activating another circuit I am building.

Reply to
tranerm

Google had a number of hits for me using "temperature activated relay circuit". This page has a simple circuit.

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Relays.pdf

A computer mouse is not doing ir. And I think most house alarms do motion, not ir either. Is what you mean to say that you need to be able to point it at the heat source rather than have the sensor on the heat source? Like these?

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(FlukeProducts)

If so that will take a more complex circuit.

Reply to
jamesgangnc

The circuit in the link you gave is misleading... the "IR" aspect is only that you can operate the controls with a TV/VCR-type IR remote control. Still uses conventional contact-type temperature sensors.

IR (non-contact) temperature measurement can get quite involved (and expensive). Do you really need this? If you just need simple contact-type probes, it can be much simpler. If you don't need to go much over 150C, you can buy a ready-made single-chip sensor. Or use a simple silicon diode as the sensor. To do that, you put a constant current through it and measure the voltage across it (basically, and ohmmeter circuit... you can use a cheap DMM to experiment with). The apparent resistance is inversely proportional to temperature, and it is *very* linear, from near absolute zero up to the point the junction melts. Calibrate with an ice bath and boiling water.

So to make your whole circuit, you can use a single-transistor current source driving the diode, and an op-amp comparator looking at the voltage on the diode. The comparator then drives a power transistor to operate your relays, etc.

Best regards,

Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!

Reply to
Bob Masta

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That\'s not how they\'re designed to work. In essence they\'re designed to
be saturated switches when hit with IR, and fully open when they\'re not.
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Reply to
John Fields

tranerm asks

If you base your circuit on an IR sensor you will have a lot of problems, because IR is everywhere. You'll get false positives from normal lights and even clever circuits which try to auto-adjust for the average background level can get fooled by, say, a cloud passing across the sun. Also - how are you going to calibrate it? And protect the high gain circuitry from RF pickup when someone uses a mobile phone below it?

May I suggest a simpler approach like this:

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dp/1006849

this kind of component, a "thermal switch", is widely available. I used one recently partly because I noticed this particular shape is some kind of standard, so even if that manufacturer goes bust Honeywell and some other bunch will still stock them.

The main problem with this item is that it is normally closed. But if you're happy to burn a bit of power and continuously power a relay (20mA?) that's OK. An IR circuit would burn a bit of power anyhow.

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Nemo
Reply to
Nemo

:
r

Sorry about the false diagram and not enough info): I am building a small turret that will first seek brightness (in a dark room, so for example, a candle) and then when the IR sensor is facing it, activate a series of relays, some ceasing motion of the 'turret' and one trggering a pump which will squirt a spray of water in the direction of the candle or other type of flame. The distance is required because I want to be able to move the candle and still have the turret track a different location. If possible, I would also like to have the sensor indicate once the temperature has gone significantly below combustion point and track a different target. If possible. Thank you for your patience and assitance(:

Reply to
tranerm

I will be runninf it off a a wall wart so power won't be a problem, but the interference probably would be. I am trying to build a small 'turret' that will first seek brightness (in a dark room, so for example, a candle) and then when the IR sensor is facing it if the IR sensor detects heat above a certain level, activate a series of relays. One or two of these will shut down the motors moving the turret, and another will activate a small pump that will squirt water, extinguishing the flame. From there, if possible I would like it to seek another target if the detcts temp below a certain level. (however this is purely an extra) I want to be able to switch the locations of the candle, so I can't reallly just run temp relays back and forth either, unfortunately. Thank you incredibly for your help(:

Reply to
tranerm

The Nintendo Wii handset (available separately) has in it a neat little infrared image sensor that is quite capable of sensing rthe direction of a candle flame. it doesn't have a simple output that you can wire straight to a motor driver though, you'd have to put a microcontroller in-between to interrogate the sensor.

some electronics hobby mag did an article on it a while back.

And there's stuff on the web too.

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so buy a used wiimote and rip the image senor out of it.

Reply to
Jasen Betts

Except for the wall-wart, your description sounds almost exactly like an entry for the "Firefighting Robot" competition. The robot has to negotiate a "house" to find the room with the candle, and put it out. You might want to check on what others have done, and the problems encountered.

In the competition, the "house" is a small maze of rooms with no roof, in a big auditorium that has overhead fluorescent lights that can interfere with the sensors. There were articles in Circuit Cellar several years ago, but I don't recall what the best solution turned out to be.

Best regards,

Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!

Reply to
Bob Masta

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