First Project: Fully controlled Terrarium for geckos


For christmas my girlfriend gave me a ardiuno mega, which i'm planning to use for automating my terrarium.
However, i'm not much of a programmer, nor electrician. So I'd like some help on this one.

The terrarium will be used to a pair aboreal nocturnal geckos, which i'll hopefully get somewhere in the next year.
The relative humidity will be around 80ish %, which need to be concidered in in the choice of sensors. The terrarium will be 60x50x120 (in cm, lxdxh) made in wood (still need to decide which sord)

My idea was to try doing the following:

-Control temperature, make the temperature more or less constant, with a 'hotspot' on the top of the terrarium.
-Control Relative humidity by spraying with a nozzle that's attacted to a stepmotor, so it can spin around 120° (and spray most of the terrarium) for this I'd like to use small pump
-Create a day/night cycle with lights (2x 5.0 UVB lights)
-The temperature and humidity also need to be in a day/night cycle, at night it needs to cool down alot, down to 15°C in the winter.
The temperatures and humidity levels i'd like to have are:
in summermonths: daytemp: 25°C, day humidity: 60-70%, night temp: 18-20°C, night humidity: 70-90%
in wintermonths: daytemp: 19°C, day humidity: 50-60%, night temp: 15-16°C, night humidity: 60-70%
-eventually make it so that it changes automaticly to summer/winter if its a specific date.
-If possible make some sord of screen where i can read what the temperature and the humidity level is in the terrarium.

This means i need to be able to cool and warm my terrarium, since i can't get my room down to 15°C..
So now what i'm asking everyone here: What sensors should i use? Can someone help me with the code or somehow write it?
I know this is a lot to ask, but every piece of help is welcome, tips are welcome too ofcourse.

Also, is there any way to test the ardiuno program without having to use your ardiuno and connect the sensors?

Thanks in advance,

This is quite a major project, especially for a starter. The usual advice is to start small and figure out how to accomplish each part of the project before putting the various pieces together.

In your case, the sensors and the code will not be the major issue. Instead, the major issue will be how to modify the environment of the terrarium in a sensible way. You want to have the ability to heat, cool and adjust the humidity, and those are hardly trivial.

Furthermore nothing can be tested until that part of the project is fully operational. So, my advice is to build the terrarium box, and then figure out what will be required to control the temperature. A Peltier device can both heat and cool, so that might be a place to start, but Peltier devices require very high currents (many amperes) at 12 or so volts which the Arduino cannot directly control without additional circuitry. So, that will be a significant challenge. Then tackle the humidity modifier. When all that is functional, then figure out how to add the sensors to set the desired environment.

Sounds like fun!

The problem is that i'm planning to make a background in my terrarium, own made, not premade stuff. Meaning i already need to place in the sensors etc. So i'd really need to know what i'm going to use as sensors, humidity controlling isnt really that nessecary, if i can program it so that it sprays twice a day it's also fine.

Also, about that peltier element, doesnt it cool and heat at the same time (just one side cooling and one heating?



A Peltier element (also known as a thermoelectric heater or cooler) is actually a heat pump. One side is connected to the box whose temperature is to be controlled and the other is connected to the outside air with a radiator (or more properly a finned convector). The direction of heat flow is controlled by the direction of the current flow. So, if the terrarium is being heated, the outside element will get cold and vice versa.

So if I’d make it so that the backpart sticks out of the terrarium through the backpannel and the background, and the front in the terrarium it would be able to work properly?


That would work, but passive air/heat flow within the terrarium might lead to significant temperature differences between different areas, like front to back. A more elegant approach might be to use a quiet, low speed fan to circulate air from the terrarium through tubing to a separate small box that houses the "inside" portion of the Peltier device. Then you would need just a couple of airflow openings in the terrarium.

Repeating advice above - start small - there's quite a learning curve to get over before this project is complete. You can start with simple things that will be useful later though. Get yourself a temperature sensor - a DS18B20 is a popular choice and suitable for the range you need - a waterproof one is likely a good idea but you could start with the regular one. Learn how to use it and display the temperature via serial. Libraries and example code should make this a feasible start.

Then get yourself a humidity sensor and get that working. Next, perhaps design the display you're going to use; once you figure out how many characters you need to display at once, get an LCD display big enough and learn how to drive it. Combine the above to show temperature and humidity.

This way, you can gradually get to making something that does something, even if it's well short of your ultimate goal.

Be aware of how many pins you're going to be using on the final product. It may make sense for example to use an LCD that can be programmed over serial.