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'[OT]: Temperature Switch'
2000\07\18@095819 by Roland Andrag

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Hello everyone..

I am looking for something surprisingly hard to find: a temperature switch
operating in the 3 deg C range. i.e. a straight on/off thermostat that need
not be adjustable (but could be). The load being switched draws 1 mA or so
at 220 V (a relay coil).  Has someone seen what I'm looking for?

Thanks
Roland

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2000\07\18@101108 by Dale Botkin

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On Tue, 18 Jul 2000, Roland Andrag wrote:

> I am looking for something surprisingly hard to find: a temperature switch
> operating in the 3 deg C range. i.e. a straight on/off thermostat that need
> not be adjustable (but could be). The load being switched draws 1 mA or so
> at 220 V (a relay coil).  Has someone seen what I'm looking for?

Dallas DS1620 programmable thermometer/thermostat and a suitable relay
driver will do this.

Dale
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The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
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2000\07\18@101316 by Andy Howard

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> From: "Roland Andrag" <spam_OUTrandragTakeThisOuTspamICON.CO.ZA>

> Hello everyone..

> I am looking for something surprisingly hard to find: a temperature switch
> operating in the 3 deg C range. i.e. a straight on/off thermostat that
need
> not be adjustable (but could be). The load being switched draws 1 mA or so
> at 220 V (a relay coil).  Has someone seen what I'm looking for?

Yes, there's one in my fridge, but you can't have that.  :>

Seriously, a supplier of spares for refrigerators would be a good place to
start.
Or a scrapyard/recycling centre if you only need one.

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2000\07\18@113707 by Craig Lee

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I am currently building just such a beast!

It turns off at 90F, and turns back on at 85F.  This is a simple Schmitt
trigger implemented using a LM2904 op. amp with a thermistor sensor. The
supply is 12VDC. The output is a SPST relay with 10A contacts.  They cost
me about $20US to make, but I am considering volume production (10,000+).
There's even a green LED to indicate operation.

Temperature range is adjusted by changing fixed resistor values.

The Dallas units are great too as the thermo-sensor is already built in.
The range and setpoints are digitally adjustable, and there is an open
collector output.  The only issue I have with it is the package is too
big to remote mount, let alone the PCB you install it on.

Craig

> {Original Message removed}

2000\07\19@010158 by w. v. ooijen / f. hanneman
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> I am looking for something surprisingly hard to find: a temperature
switch
> operating in the 3 deg C range. i.e. a straight on/off thermostat that
need
> not be adjustable (but could be). The load being switched draws 1 mA or
so
> at 220 V (a relay coil).  Has someone seen what I'm looking for?

Two chip solution: an LM75 or DS1620 + a 12c508 to set the switch point?

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2000\07\19@010759 by Dale Botkin

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On Tue, 18 Jul 2000, w. v. ooijen / f. hanneman wrote:

>
> Two chip solution: an LM75 or DS1620 + a 12c508 to set the switch point?

You don't need the PIC for that.  Once set, the DS1620 will retain its
settings.  You could have a 1620 setup box (PIC based, of course!! ;-) to
program the thermostats before insertion.

I've got a DS1620 .H file, if anyone needs C code for it...

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

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2000\07\19@160157 by Spehro Pefhany

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At 03:48 PM 7/18/00 +0200, you wrote:
>Hello everyone..
>
>I am looking for something surprisingly hard to find: a temperature switch
>operating in the 3 deg C range. i.e. a straight on/off thermostat that need
>not be adjustable (but could be). The load being switched draws 1 mA or so
>at 220 V (a relay coil).  Has someone seen what I'm looking for?

Sounds like you just need a thermostat. There is a type that looks a bit
like a TO-3 transistor case, but with a couple of spade (Faston) connectors
on
the 'bottom'. They are surprisingly accurate and cheap (at least in large
quantities, cheaper than semiconductor solutions by far since they include
both a sensor and a power switching device and require no power supply).

The main limitation is that the differential (hysteresis) between on and off
temperatures has to be fairly large (several degrees C, IIRC).

Try an appropriate directory for your location, these are more appliance
parts than electronics items.

Best regards,
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2000\07\19@163735 by Peter L. Peres

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>3 deg range, 220V 1mA

If by 3 deg range you mean 0..3 deg C then look for a 'garage thermostat'.
These are made to turn on the heating in the garage in cold countries,
when temperature drops to the frost point, to avoid obvious problems and
wall cracking by ice. Also sensors for automotive use exist (even in kit)
for frost warning (icing). They have relay outputs.

If by 3 deg. range you mean just 3 deg hysterezis in the 0..100 deg C
range then you want an industrial rail mount thermostat with 2% precision
class. This will usually switch 10 or 16A directly so you need no relay.

If you want to build one, then pick a sensor (chip or thermistor) and
build it.

And last, if you have to turn on heating to avoid freezing, and have no
other resources, then use a fridge thermostat as is (not the deep freeze
kind). This will switch 8A inductive usually, and is EXTREMELY reliable.
MUCH more so than all the others combined probably. Also very cheap (~$10
in ones). And this is off topic as it has no PICs.

Peter

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2000\07\24@052917 by Roland Andrag

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Thanks for all the replies!  I have found and will be using a thermostat
normally used in fridges.

Thanks again!
Roland
{Original Message removed}

2000\07\24@114239 by Craig Lee

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How much is it and what are the specs?

Craig

{Quote hidden}

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