temperature activated switch help..

[arclite5]

So I have no idea what I'm doing when it comes to this type of stuff but I really want to learn some basics when it comes to electronics.

What I want to do in this particular application is have a cooling fan activated by a temperature sensor. Once the sensor detects a "greater than or equal to" a certain temp, I want it to activate a cooling fan, and then deactivate that fan once the temp falls below said threshold.

Where would I go to learn about building this type of switch? I assume I'd have to do some sort of programming also?

Thank for anyone who takes the time to help guide me here..

[rc_sjo]

You could do it with a thermistor, comparator and transistor/fet.

[lazy-b]

If Weight is not the issue. you can just simple add a Thermal Switch....there are many different range of thermal switch.

[orraman]

.
If you want to learn about electronics and gain experiance in programming, jump right in. No programmer is needed, download is though 3 wires on a 9 pin serial plug.

I have an 8 pin Picaxe 08M microprocessor reading a digital sensor and controlling a 240V, 3 KW fan heater via a solid state relay. Not the cheapest sensor but the Picaxe has a dedicated routine for it and the interface is a single 4K7 resistor.

You could download the Free Programming Editor from www.picaxe.co.uk , copy and paste this simple programme into the editor and click on the Simulator, and change Generic up and down.

Any assistance I can offer?

Dave

' all after ' is comment and ignored
'thermostat picaxe 08M, DS18B20 on GPIO 1
'fan on GPIO 4

start:
pause 1000 '..............delay 1 second
readtemp 1,b2'..degrees C in variable b2
if b2 > 30 then fan'....test, is temp high
low 4'....................switch OFF fan
goto start
fan:
high 4'....................switch ON fan
goto start

[JohnMuchow]

No need for a microprocessor or any programming (though you would learn a lot using one for this simple project). As lazy-b mentioned, you can use just a thermal switch to turn power to the fan on/off. They come in two types; normally-open and normally-closed.

Normally-open means that the two contacts in the switch are open until the surface the switch is mounted on is at or above the switch's activation temperature. You can get switches with activation temps. from 85C up to 150C and above. Normally-closed means that the two contacts in the switch are closed until the activation temp. is reached, at which they open.

For both types, the switch will "reset", or go back to its resting position, after the temperature drops about 10C below the activation temperature.

There are many, many different types of temp switches out there in many sizes and mounting styles. Here are the ones I use: http://www.cantherm.com/products/thermal_cutouts/encap_therm.html

But, if you want to get some learnin' on, the PICAXE series of processors are a great way to start. :D :D

[Dan Baldwin]

At the bottom of this (http://mouser.com/catalog/catalogUSD/638/1959.pdf) page, you'll find a range of thermostats all the way from 55 deg F to 335 deg F for under $5.00 ea. Differential is a bit high at about 30 deg F. You would need one that closes on rise.

Dan

[arclite5]

Thanks, I think you've all helped to get me started here.. I'll see what I can figure out on my own and if I run into any more snags I'll come bother you all again ;]

-Kyle