Re: IR Temperature Sensor

On Mar 4, 5:59 am, N0S...@xxxxxxxxxxx (Bob Masta) wrote:
On Tue, 3 Mar 2009 17:11:07 -0800 (PST),



tran...@xxxxxxxxx wrote:
On Mar 1, 2:14=A0pm, John Fields <jfie...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Sun, 1 Mar 2009 13:44:43 -0800 (PST), tran...@xxxxxxxxx wrote:
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 tran...@xxxxxxxxxx

---
What do you mean by "IR temperature sensor"?

JF =A0

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.

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(:
.

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