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temperature controll

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klayus

New Member
i'm a begginer in electronics and i will really appreciate some help.
i'm trying to build a temperature controller (analog cause i dont have enough money for all the digital equipment and i lack the experience) that controls a aquarium substrate heater(heater cable aka HC) and a water heater.

the theory is this:

i have 3 sensor: 1 for the substrate, 2 for the water just above the substrate and 3 for the water column.

i want to measure and compare 1 and 2. the HC must operate as long as there is a difference in temperature between 1 and 2(2 beeing smaller than 1, if 2 = 1 then the HC stops).
if the water temperature drops below a set value(26 degrees celsius ) than the water column heater starts.

i would like to see the temperature(i will think about this) and an on/off HC LED.

please help. tons of beer for anybody who helps if you ever come to Romania.
 
Last edited:

stevez

Active Member
I have a few questions:

A. What is an aquarium substrate heater?
B. What is the water heater that you describe?

Please describe the water temperature that you would like to maintain and how much variation you can tolerate.

It's ok to IM me if that helps.
 

MOSFET KILLER

New Member
Use a thermistor and a resistor to make a voltage divider and connect that to a comparator, use a zener diode to set the reference voltage on the comparator, this unit will need some calibration of the thermistor and the resistor to land on a specific temperature. Use this circuit to drive a relay to control the heater.
 

klayus

New Member
@MOSFET KILLER - can you help me out a bit more??? something like a schematic or at least the parts. my only experience with electronic is a small stereo amp a few years ago so what you told me helps a lot but not enough to get started :D
 

olly_k

Member
ok if this is a specific college project then ignore what I am about to say....

Sub heaters are a complete waste of time for planted tanks ;)

Also, I am sure sub heaters are deliberately low powered so as not to require a thermostat but as I have never used one and never will I am not sure about that!
 

Lighty

New Member
I agree with olly k.

unless there is a specific reason why you need to use a sub heater then just use a normal heater, as if there is water movement, which I'm sure there will be, using both would be a waste of time?

Perhaps a LM3914 dot/bar graph could be used to display the temp?
 

klayus

New Member
hey

i have a friend here where i live and he has 2 tanks (almost identical - same plants same fishes) and you can really see the diference. for me it has a purpose.

can you guys help me with an ideea or a schematic? thanx a lot
 

olly_k

Member
Hi Klayus, assuming a substrate heater did make a significant difference (I am sure Tom Barr / Dianna Walstead will tell you otherwise ;) ) what will you hope to achieve by having two thermostats as opposed to one? If using only one element you only need one thermostat (i.e. I can't see what purpose stat #1 serves?)

Also how does your friend control his sub-heaters?
 

richard.c

New Member
Hi Klayus,

I understand what you are trying to do, however I would just like to add a bit of practical experience if I may.

The substrate heater, typically an in tank heating coil or under tank foil heater, should have a very low wattage, just enough to keep the subtrate very gently heated.
If you have to control it regularly with a thermostat then that tends to imply the heater is too strong.
The circulation of the water, even in a planted tank should be enough to disperse the temperature though out the tank.

I would doubt that a probe in or just above the substrate would be very effective. I would leave my substrate heater on all the time, running on the main thermostat and heater, however if the whole tank temp increased too much, say in summer, then the substrate heater would be switched off.

You say you can only afford to go the analogue way, but to be honest that is not practicable as the on / off hysteris of that type can be very wide.

A simple little pic micro with cheap thermistor sensors will allow you to control things to 0.1deg C very easily.

You can see my controller details in this forum, although evolving into a large thing you can still build a simple version with just one or two controls. https://www.electro-tech-online.com/threads/marine-controller.98926/

Hopefully it will give you some ideas, the principle can be applied to three sensors if you want to follow that route.

hth
 

cbiblis

New Member
This is a start, this is my differential thermostat i use for my solar hot water heater. You will have to add a 120v/12v transformer to power the circuit, then add relays accordingly. Also you'll have to isolate the sensors maybe with glass straws and silicon. Or maybe this won't help at all but here it is.
 

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ok if this is a specific college project then ignore what I am about to say....

Sub heaters are a complete waste of time for planted tanks ;)

Also, I am sure sub heaters are deliberately low powered so as not to require a thermostat but as I have never used one and never will I am not sure about that!

:confused:

Sub heaters are about the best thing you can do for a planted tank;
- even temperature for a given depth
- accelerates the decomposition of the mulch
- allows plants to absorb the mulch faster and thereby promotes plant growth
- the water convection through the sand provides a form of filtration
- it is widely accepted that plants like "warm feet"
- sub heaters are underpowered so as not to damage the plant root system through overheating

klayus,

if you are attempting to even the temperature throughout the tank then I would think again.

In nature there are natural thermoclines in the water. These are inversion layers where one layer is at a different temperature the other. Fish move through these layers and use them to find comfortable temperatures. Not all fish like exactly 26°C, this is a best fit temperature.

Regards
Andrew
 

olly_k

Member
Well my friend you seem to be at odds with MOST of the aquascaping community! Do you not consider Tom Barr to know what he is talking about for instance?

Only article I can find which suggests sub heaters are ok is PFK but they seem to think biorbs and those new fangled sealed top tanks are ok so hey they know their stuff!

Anyway, would love to see the links to the results of a well controlled test please?

:confused:

Sub heaters are about the best thing you can do for a planted tank;
- even temperature for a given depth
- accelerates the decomposition of the mulch
- allows plants to absorb the mulch faster and thereby promotes plant growth
- the water convection through the sand provides a form of filtration
- it is widely accepted that plants like "warm feet"
- sub heaters are underpowered so as not to damage the plant root system through overheating

klayus,

if you are attempting to even the temperature throughout the tank then I would think again.

In nature there are natural thermoclines in the water. These are inversion layers where one layer is at a different temperature the other. Fish move through these layers and use them to find comfortable temperatures. Not all fish like exactly 26°C, this is a best fit temperature.

Regards
Andrew
 

klayus

New Member
hey

ok this is getting a bit offtopic. it dosent matter if people accept that the substrate heater is a good thing or a bad thing. i love electronics and aquariums so i'm trying to do a little of both.

i'm not trying to even out the temp in the tank. only heat the substrate a little so convection occurs. a heater cable is underpowered. it only heats the water around it which tends to rise which is replaced by colder more oxigenated water above and so on. that will eventually heat the substrate up a bit. when that happens i want the HC to be turned off so the substrate cools down. i may not fully understand how a substrate heater works or what a controller actually does but i'm thinking my ideea would work.

i really dont care what Tom Barr / Dianna Walstead thinks. they have great experience and beautifull tanks but how long do they keep them? enough to take a picture of them(i'm not sure and this is irelevant also). i have proof that it works so i wanna try it.

richard.c has a great plan for a controller and i'm gonna give that a try. i'm pretty sure this is an electronics forum so let all stick to that ;) (no offence to anybody)

(PS if i make a lot of spelling mistakes excuse me but i just started learning english 3 months ago)
 

hoooo

New Member
hi every body i am new memeber my name is hoooo i am looking for temperature alarm sensor circuit(rang 0c-100c) this is my final year project help ...
 

hoooo

New Member
thanks cbiblis but i cant get the kty10 sensor in the market at my place do you know it other sensor can subtitute for it
 
Here is one of my favorite circuits, the parts can be picked up at radio shack, except maybe the thermistor.
 

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