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Controller for lighting, temperature, humidity, etc.

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New Member
I'm new around here, but I've been lurking for a while.

I just finished a class that had to deal with programming the 6812, and I am interested in developing a project around the microcontroller.

My goal is to build a unit capable of controlling all environmental aspects of a terrarium I am in the process of designing/building. The dimensions of terrarium are approximately 4' x 2' x 2'. I hope to be able to build a dry area on one end with a 4-6" deep pool of water on the other. If time and money allows, I hope to add a water fall and natural looking transitions from land to water. The overall goal is to achieve a natural as possible environment.

I plan on keeping several species of planets, a few fish, and eventually a snake in the enclosure.

My goals for the control unit are as follows:

-- 3-4 temperature zones (temp range 20*C - 40*C) monitored and adjusted via infrared light bulbs and/or heating elements. All of the temperature zones will follow a natural rising and falling behavior that mimics natural weather patterns.

-- A humidity monitor and adjustment system that also follows a natural pattern.

-- Control of a full spectrum florescent bulb that mimics the gradual rising and setting of the sun.

-- A timer system for watering the plant life within the tank. (Using a constant pressure/control aperture distribution system)

-- An alarm system that monitors both high and low conditions for all temperature zones individually

-- A system pause button for when the cage needs to be opened for cleaning or maintenance purposes

-- A LCD monitor that reads out the different temperature readings, humidity readings, and lighting percentage for easy viewing on the front of the tank

I'm pretty sure I can handle most of the programming aspects of this projects (with a lot of help from my professor of course). My technical knowledge of actual circuit design and building is at most so-so. I have taken all of the intro and some of the upper division EE classes on circuit design; however, due to the SERIOUS lack of actual design and construction of electronic devices in the curriculum, I am less than certain how to implement many of the features I would like in my unit.

I'm sure as my progress advances with this projects I'll have plenty more questions, but for right now I have a few basic questions I was wondering if anyone could answer.

1.) What type of thermsistors would be best for this application, and where could they be purchased? I looked on the internet and found a lot of information, but I had a hard time deciding what would work best.

2.) Similar to above, but for a humidity sensor. I am trying to keep the project as inexpensive as possible, so I don't have a need for perfect accuracy in either the thermsistors or humidity monitor just something workable.

3.) All of the heating elements are 110V AC driven units. What is the best way to control these type of devices with a microcontroller? What type circuitry is needed after the output pins of the 6812?

4.) I run into a similar problem to above with the lighting except it's a little more complex. I'd like to be able to have varying levels of light to mimic sun rise and set. What all would be necessary to implement this?

5.) Where could I local some small electrically opened valves for the watering system?

Before anyone asks, I'm pretty set in using the 6812 because I just finished the class and feel very confident in my programming ability with the controller. On top of that, I have access to a VERY high quality simulator and debugger along with access to the professor that wrote the software and has written multiple text books on the 6812 and its applications. However, if anyone has some convincing arguments on why I could use another controller, I am all ears.

Lastly with this post, I am not necessarily looking for just answer to questions, but more of a nudge in the right direction. I am going to try to make this project a learning experience for myself.

Thanks for any help you can give,

- Matt
You can get a combined temperature and humidity sensor (as a free sample) from, it's a SM device, the SHT11. I've got one, but not had time to play with it yet.

As for your choice of processor, there's no 'right or wrong' in such matters, most people will simply use the one that they are most familiar with - the 6812 would be fine.
Funny, I'm working on a project that is quite similar to that :). Thanks Nigel for the hookup for the humidity sensor. I've been trying to find something like that for a while.
Reading Material

Have a look here:

**broken link removed**

Download the Industrial Control and the Applied Sensor/Earth measurements books (They are free to download).

You will just have to make adjustments with respect to the specifics of the microcontroller you are using but I assume you have a TTL type setup so it shouldn't be too bad to cross over to your equipment.

I used this material for many different controllers I have, it helps when you are just starting out with these types of things. This was my first microcontroller project a few years back:

**broken link removed**

How are you going to have all those different zones in such a small box?

You could use triacs to control the light and heaters. Look up logic level or sensitive gate triacs. Teccor is a common mfg, or you could interface using opto triacs. Teccor has some excellent app notes on the subject. Using phase control, you could vary the intensity of the light and heat.

The SHT11 is very cool. I have been using them for about a year.

I have some most excellent thermistors that I would recommend-- if I could figure out the pn. I have a bad feeling they might be custom. I think they're by Thermometrics, though.

Little valves? I dunno, check like,, or the electronics goldmine.

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