Thumbelina: an Automated Indoor Greenhouse

Once upon a time there was a woman who lived alone and wished have a daughter, so she expressed its desire to a good fairy, who gave her a small seed.

The woman planted the seed in its garden and after some days from a flower come out a small girl tall as a thumb. The girl was loved by everyone and she helped this mother with plants of the garden, its name was Thumbelina. This project takes its by this famous story and, as Thumbelina, goes to maintain a small, indoor and vertical greenhouse.

As previously said all the system is managed by an Arduino Board, in particular it was designed to control until four different layers. Arduino controls some actuators as the water pump, the lights and the fans in a unique way for all the layers and the valves in a separate way for each layers. Each actuator is associated to a sensor and Arduino trivially, operates on an actuator when its sensor returns a value upper than a certain threshold. The time with which Arduino makes an operation rather than another depends by the kind of operation (e.g. check the moisture at each hour) and by the some specific that could be defined by the user (e.g. give the light to the plants at least for ten hours). The electronic schematic is divided into two major parts, one on the left of the Arduino, which contains the sensors each one connected to an ADC channel of Arduino, and a part on the right of the Arduino board which contains the actuators.

The detection of the ground moisture and then the irrigation is the most important part, not only for the alive of the plants but because it should manage four different layers. So the hardware developed provides the use of four different moisture sensors, four different valves and a water pump.

The control strategy is simple, in every step, which happens each five minutes, Arduino reads the moisture sensors and if one of these values is below than a certain threshold, it will activate the water pump and will open the valve of the layer associated to this value; the other valves remain closed and the water flows only in the desired layer. The water can be taken by containers or using a powerful electrovalve (as the valve inside the washing machine or the dishwasher) and a relay driven by Arduino, it is possible take it from the home network. Anyhow the cores of this irrigation strategy are the valve inside the greenhouse, which were developed and then 3D printed in order to maintain them closed when these ones are not powered, and to be powered and opened hence only when it is necessary. As shown in the figures the valve is composed by two master pieces a top part and a bottom one.

The top part contains only the shell for the micro-servo and a pulley which goes on the shaft of this last one. While the bottom is composed by a shell in which there are an access and an exit for the tubes in which the water flows and the locking mechanism. This last one is composed by six small pieces, in particular a bolt is fixed to the shell by a nut and it drives a spring. The spring pushes a flange and this one contains a cylinder of silicone which works as a plug, closing the hole where the water enters. Summing up, the spring, pushing the plug of silicone does not allows to the water to enter inside the valve, to delete the action of the spring and open the valve, a small rack is attached to the flange and coupled with the pulley of the servo. When the user wants open the valve, he should control the servo, pulling back the flange and hence the plug of silicone, after if he wants close again the valve he has to power down the servo and let operate the spring.

Many parts of the valve, as the shells, the pulley, the rack and the flange were 3D printed, so, depending by different 3D printers or printer techniques the final pieces may have leak of water. A simple way to overcome to this problem is to stretch a layer of silicone inside the shells, furthermore I suggest to put another layer of silicone along the junction between the top and the bottom parts of the valve. While about the moisture sensors were used commercial sensors even if it is possible to obtain good results using homemade sensors made, trivially, with two nails.

Depending by the plants which we want have in our greenhouse the amount of daily light for them could be very important. So a simple light detector is inserted in the greenhouse and this choice allows to the Arduino board, which manages the greenhouse, to manage also the amount of daily light. Basically the Arduino board every day measures the amount of natural or external light, if this one is under a certain threshold, Arduino switches on the lights ,which are inside the greenhouse, and to maintains powered on them until the total amount of light reach the threshold. The user can set the time threshold for the light and the control is the same for all the layers

For the lights were used commercial lights, designed to stay outdoor, in order to be unharmed by the condensate.

The same considerations made for the light can be made for the temperature, in fact, depending by the plants that we want grow an excessive warm can damage them, to overcome this problem a sensor of temperature is inserted inside the greenhouse. Trivially at each loop the Arduino board reads the value of the temperature and if it is over a certain threshold, Arduino switches on the fans and provides to cool down the greenhouse. With the existing hardware it is not possible to warm up the greenhouse but it was designed to stay inside an home, so its temperature should be always over a minimum value. Four different fans, one for each layer, are used to cool down the greenhouse and they are activated together. In these project are used four fans, recovered by old power supplies of desktop computers