IR Temperature Sensor

[[email protected]]

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.

http://www.electronics-lab.com/projects/test/023/index.html

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 [email protected].

 

[[email protected]]

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.

 

[[email protected]]

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.- Hide quoted text -

- Show quoted text -

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

http://www.cornerstonerobotics.org/curriculum/lessons_year1/ER Week18, 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?

http://us.fluke.com/usen/products/F...FlukeUnitedStates&category=THE(FlukeProducts)

If so that will take a more complex circuit.

 

[Nemo]

tranerm asks

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.

http://www.electronics-lab.com/projects/test/023/index.html

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 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:

http://uk.farnell.com/honest-well/t23a150bsr2-15/thermal-switch-nc-150-c/
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.

 

[[email protected]]

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

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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

 

[[email protected]]

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:

http://uk.farnell.com/honest-well/t23a150bsr2-15/thermal-switch-nc-15...
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.

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

 

[Jasen Betts]

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

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.
http://blog.makezine.com/archive/2008/11/hacking_the_wiimote_ir_ca.html

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