Temperature Relay Circuit Required

D

Daren Hawes

Guest
Hi
I have a fish tank that if it gets around 28 degrees Celsius I need to
turn on some fans. Can anyone help me with a simple circuit that will.

1. Maybe use a thermistor to measure the temp of water. I will obviously
need to water tight the test probe. That's easy!

2. Have a variable resistor so I can calibrate. I already have a digital
thermometer that measures the tanks temp.

3. Have the circuit switch a 12v relay when it reaches > 28 degrees (28
or more). I will need to calibrate via VR.

4. Turn off when temp gets below 28.

Something simple with maybe an over ride "On" switch?

Thanks Heaps. I am familiar with electronics, just not design.
 
"Daren Hawes" <newsgroups@webdesignmagic.com.au> wrote:

Hi
I have a fish tank that if it gets around 28 degrees Celsius I need to
turn on some fans. Can anyone help me with a simple circuit that will.

1. Maybe use a thermistor to measure the temp of water. I will obviously
need to water tight the test probe. That's easy!

2. Have a variable resistor so I can calibrate. I already have a digital
thermometer that measures the tanks temp.

3. Have the circuit switch a 12v relay when it reaches > 28 degrees (28
or more). I will need to calibrate via VR.

4. Turn off when temp gets below 28.

Something simple with maybe an over ride "On" switch?

Thanks Heaps. I am familiar with electronics, just not design.
Click to expand...
Here's a simple circuit to do that (in two formats for flexibility):

http://www.terrypin.dial.pipex.com/Images/TempSwitch.gif
http://www.terrypin.dial.pipex.com/Images/TempSwitch.PDF

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
"Daren Hawes" <newsgroups@webdesignmagic.com.au> wrote

I have a fish tank that if it gets around 28 degrees Celsius I need to
turn on some fans.
Click to expand...
Never re-invent the wheel, there are so many more interesting
(and profitable) things to do.

A little Google goes a long way:

http://www.automatedaquariums.com/lv_tsd.htm

I am sure there are lots more to choose from.
Try asking in the *.aquaria (ium?) groups.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
 
Terry Pinnell wrote:
"Daren Hawes" <newsgroups@webdesignmagic.com.au> wrote:

Hi
I have a fish tank that if it gets around 28 degrees Celsius I need
to turn on some fans. Can anyone help me with a simple circuit that
will.
Click to expand...
[snip]

Here's a simple circuit to do that (in two formats for flexibility):

http://www.terrypin.dial.pipex.com/Images/TempSwitch.gif
http://www.terrypin.dial.pipex.com/Images/TempSwitch.PDF
Click to expand...
Hysteresis would speed up the on/off transitions and prevent relay chatter
near the threshold point. Consider adding a large resistor (1M) from the
op-amp output to the +ve input thereby providing a small amount of positive
feedback.
 
Nicholas O. Lindan wrote:
"Daren Hawes" <newsgroups@webdesignmagic.com.au> wrote


I have a fish tank that if it gets around 28 degrees Celsius I need to
turn on some fans.


Never re-invent the wheel, there are so many more interesting
(and profitable) things to do.

A little Google goes a long way:

http://www.automatedaquariums.com/lv_tsd.htm

I am sure there are lots more to choose from.
Try asking in the *.aquaria (ium?) groups.
Click to expand...
Now that product packs a lot of punch for the price.
 
Daren Hawes wrote:
Now I am a little confused.

The circuit simply needs to...

1. turn on fans when the temp goes over 28 and
2. turn off when the temp drops below 28 again.

So whenever the tank is hot fans are on and whenever it is not fans are
off.
Click to expand...
Thermostats do not operate that way because you have no control over the
cycling of the fan- they will go ON/OFF-ON/OFF-ON/OFF- etc in some
indeterminate way. If that's what you want, it would be better to use
speed control of the fans so as to maintain the temperature at constant
28oC. Are your fans 12VDC "brushless"?
 
On Sun, 28 Nov 2004 03:49:37 +0000, Daren Hawes wrote:

Now I am a little confused.

The circuit simply needs to...

1. turn on fans when the temp goes over 28 and
2. turn off when the temp drops below 28 again.

So whenever the tank is hot fans are on and whenever it is not fans are
off.

Is this what the first circuit will do?
Click to expand...
One of these for 28C, in series with the fan motor:
http://www.ti.com/snc/products/controls/ptherm-probe-xtemp.htm

You'd have to check for distributors in OZ - but it certainly could do no
harm to find a pet store and see what they have off the shelf.

Good Luck!
Rich
 
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