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DIY Terra Control

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#1 Stefan S.

Stefan S.
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Posted 08 July 2012 - 22:53 PM


I want to introduce you to my latest project: A DIY "Terra Control" device for controlling temperature and humidity.
Perhaps it's useful to other people beside myself.
If you buy those devices from your local (or online) pet store they tend to be quite expensive, despite the fact that they are really very simple. Just a sensor for humidity/temperature plus a human interface plus a relay connected to a power plug.
As I was searching for an idea for a new microcontroller poroject I thought: "Why not build one of those myself?"

And here's the result:

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selectable target day and night temperatures
adjustable daytime (from 6 to 23)
selectable target humidity
switching between heating and cooling mode
switching between heating/cooling according to daytime or heating/cooling off
3 buttons + LCD as user interface
1 Power plug for a heating device (e.g. heating cable, heating mat)
1 Power plug for a cooling device (e.g. a fan)
1 Power plug for a humidifying device (e.g. a fogger)

Now for the used hardware:
Atmel Atmega8 microcontroller
LM35 temperature sensor
DHT-11 temperature and humidity sensor
PCF8583 real time clock
3 bottons as input
1 LCD module (HD44780 compatible)
3 pieces 5 Volt relay module
1 modified PC power supply

Here's a picture of the board:

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This is the modified PC power supply with built-in (or should I rather say squeezed-in) relay modules and wiring:

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The sensors that you position inside your terrarium:

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That's what the LCD shows you (temp. day, temp. night, current temp., current time, duration of day, target humidity, current humidity, heat/cool, timer/off):

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Neary all of the parts were bought on ebay (from China) where they are very cheap.
For example: The Atmega8 costs about 4€ here at home whereas I get it on ebay for 1,10€ (free postage).

Now some quick instructions on how to build your own Terra Control:

If you know how to solder and to read a schematic (and/or make your own PCB) you can build one yourself.

The modification of the PC power supply was a bit tricky (because of the restricted space). There are lots of manuals on how to do get a PC power supply to run without a PC on the internet. You just have to solder 2 wires together and put a load of about 500mA on the supply for it to start (and continue) running.
Then it's just a question of finding the supply's 230V output (be very careful!) and solder some wires on for your relays. Then you need to find the 5V and GND of the supply (usually a bunch of red and black wires coming out of the supply) and wire those to your relays.
Then you solder your circuit together, program the microcontroller and you're ready to go. (There are programmers for 3€ on ebay).

If you're interested in the schematic and code and which parts exactly to buy on ebay feel free to contact me.

  • mantrid likes this

#2 pmatil

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Posted 10 July 2012 - 05:06 AM

Nice idea. But the power supply mod is very suspicious and doesn't look very electrically safe. Just be careful.