Mini-Eden Project

Using a microcontroller to create an artificial garden

I don't like gardening. When we grow sunflowers for the children, I forget to water them and they die. So I need to plant some more and we end up with midget sunflowers by the end of the summer. The problem is that I have no control over the environment so I decided to build my own, as a kind of experiment. I've dabbled with automatic plant watering in the past, but this time I wanted to make a whole environment that provided artificial light, water and heat. This also gave an opportunity to use a microcontroller to control everything. I like Microchip PIC microcontrollers so one of these devices ended up as the brains behind the project. As this project mixes water and power, and having children about, it needs to run at a low voltage, preferably 12 volts.

Goal

Build a climate controlled enclosure suitable for growing plants. It should require minimum human intervention and should be based on a PIC microcontroller and run from a 12 volt supply.

Plant Growing Requirements

To grow, plants obviously need light, water and heat. From the outset, I thought this would be something I keep inside the house to monitor so although it will have the capability of equalizing temperature, this would not be implemented initially as room temperature should be ok.

Lighting Requirements

With Power LEDs now becoming more prevelant, this seemed a good time to dabble with them. I believe plant's need red and blue light are less fussy about green/yellow as that would be reflected from the foliage. It seems a safer option just to go for white-light as this is what can be found in sunlight. Although I was originally intending to use power LEDs, I had two 9 watt 12 volt florescent lights that I had previously used when generating power from wind-turbines. These were small and seemed ideally suited for the task.

Moisture Requirements

The soil will need to be kept moist as forgetting to water is why I keep killing sunflowers. To achieve this, it is possible to measure the resistance of the soil, the drier it is, the higher resistance. Using a PIC with an ADC will enable the resistance to be measured. When the resistance exceeds a threshold value, then water can be added to the soil to bring the resistance back down again.

Temperature Requirements

Temperature can be measured with a bead thermister and an ADC in the PIC used to measure it and some form of heating (a halogen bulb?) used to raise the temperature. However, as the box will be inside, I decided not to implement a heating mechanism.