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Topic: Larger thermostat project (Read 2986 times) previous topic - next topic


Okay so here's the background information. I run a reptile department in a pet store and have about 30 or so housing units all connected to each other. The main problem I've had is that the heat shared between them is so great i'm plugging in 25 watt bulbs and it gets to 85 degrees easy. I was wondering what basic outline would I be looking at if I were to use Arduino to essentially make a thermostat for each individual tank. There's already an inlet I can use in each tank for temperature probes, so that's no problem. My main concerns and wants are:
1) all controlled on 1 monitor. 3 would be fine if needed because the housings are divided into three units with 12-14 housings on each unit.
2) simple interface for me and anyone else, Preferably a simple three button system (i.e. select housing up or down, Enter, Select temperature up or down, Enter)
3) fairly easy to install and be ready by deep winter. Our store has extremely poor insulation so its cold for my reptiles at night.
I really hope this can be done. I spend about a quarter of my workload wasted because of improper temperatures (For me leading to no feeding, lethargic animals, mean reptiles, sick animals etc.)
What would I be needing, what basic outline of coding would I have to do. And any other install tips or tricks would I have to do?


You haven't really explained what you're trying to achieve, but if you want to control the temperature in all those enclosures, why don't you simply fit each one with a thermostat? You could make your own programmable stats with an Arduino and temp sensor plus relay drive circuit, or you could simply buy commercial ones.


Sorry If I wasn't clear. Yes I do want an thermostat for each essentially. The problem with me buying a commercial one is essentially cost. Each cage would need its own thermostat and the cheapest option are simple thermostats that cost us 40 dollars. We'd rather not spend $1200 on a system that is cheaply made and difficult to control simply because each is controlled on an analog scale that anyone could open a cage and change.


Well, I imagine you could make your own digital stat for a few bucks using a standalone Arduino and a temp sensor although you would also need to provide the output driver to power your heating device; I would have thought you could get a much cheaper and simpler solution using an adjustable otter switch though, if temperature control is all that matters. For anti-tamper control, can't you simply put the thing in a box?


Dec 02, 2012, 07:56 pm Last Edit: Dec 02, 2012, 07:58 pm by dc42 Reason: 1
What you are trying to do is not difficult, but it will be more work than a stat per tank and may not cost much less. However, it will give you a readout of temperature for each tank. Here are some suggestions:

1. Temperature sensors. There are lot of different types available. The DS18B20 is popular and has the advantage that you can connect several of them to a single Arduino pin. However, getting them to work when you have long wires between the Arduino and multiple sensors can be tricky. See http://www.maximintegrated.com/app-notes/index.mvp/id/148 for some advice. Alternatively, you could use analog sensors such as LM35 or TMP35, which can work over long lead lengths, but you would then need to add analog multiplexers such as CD4051 if you want to read more than 6 of them.

2. Controlling the heaters. For controlling 25 watt lamps (or preferably, power resistors instead), power opto triacs would be suitable. The maximum rating you can get easily is 1A, for example http://www.farnell.com/datasheets/1244300.pdf. If the heater current is more than this then you will need SSRs. You will need one per tank.

3. Display: either a character LCD or a graphic LCD is easy to interface to an Arduino.

4. Controls: I suggest two rotary encoders, one to select the tank and the other to select the desired temperature.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.


This sounds like a perfect project for 555: simpler and cheaper.

I would use a constant-on heater (light bulb in your case), and a 555-controller motor. The thermistor would control the 555's duty cycle so the colder the thermistor, the stronger the motor blows hot air into the housing / section.

This would be an energy-efficient / low noise solution that is cheap and simple to build.

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