1. Capillary Action Systems:
- Very simple.
- Low cost.
- No electricity required.
- Usually requires one water source per pot (messy, not good for many plants).
- Soil is kept moist around the clock (plants prefer a wet-dry-wet-dry cycle).
- Size of water source is limited (most of these systems come with the water container attached).
- Water source needs to be installed on top of the plants (not discreet, refill & maintenance troublesome).
- Size of water source somewhat limited (how much water are you going to put up there?)
- Systems on the market ran on batteries and gave the same amount of water to each plant.
- Requires powerful pump or connection to the water mains.
- Some systems had trouble with the tubing popping out.
- Watering volume is controlled by varying the aperture size of the outlet, which is not very precise.
After a lot of digging, I found a manufacturer of (relatively) cheap, but strong pumps. I won't reveal exactly what pumps they are, but despite their small size and price, these pumps could:
- Prime themselves,
- Draw water up to over 2.25m in height,
- Ingest small particles,
- Survive 2 accelerated life tests (5 & 10 years) with no problems.
Now, the pumps need to be controlled, and for that, I decided to employ an Arduino based system. Arduino is an open source electronic prototyping platform based on a microcontroller and a simplified programming language. Although the platform is simple enough to be understood by children, it is very powerful when taken to its full potential. The electronics it is based on is also solid technology.
|An Arduino Uno|
To give a brief overview of how an Arduino works, the microcontroller has multiple 'pins'. These pins can either act as 'input' or 'output' pins. An input pin can 'measure' the voltage it is 'receiving' (which is then interpreted by the program to mean something, e.g. a button press) whiles an output pin can be instructed by the program to deliver a specific voltage (which may then trigger something else, e.g. an LED turning on). By using these two types of pins as 'building blocks', one can create complex systems to do a wide variety of tasks.
Since the pumps required much more energy than the Arduino pins could supply, the prototype utilized mechanical relays to control the pumps. The switches basically have small electromagnets (controlled by the Arduino) that close the main circuit when activated, thus turning the pumps on. However, these made quite a bit of noise, so the decision was made to switch to a silent alternative for the final product (which I won't reveal).
|Mechanical Relay Array (Prototype)|
A custom printed circuit board (PCB) was designed for the final product. It was based off the Arduino microcontroller and incorporated the microcontroller chip, buttons, a 16x2 LCD screen, electronic switches for the pumps, protective circuits and the ICSP all on one board.
|Electronic Circuit Prototyping - The Messy Truth!|
- Power Input - Contains protection components such as decoupling capacitors, a diode for polarity protection and a resettable fuse for overcurrent protection (the Hydra PCB contains all of these components) as well as a MOSFET to regulate the voltage coming in.
- Microcontroller to USB - Enables the microcontroller to communicate via USB. This involves a separate controller chip to mediate and a few resistors in between.
- Microcontroller to ICSP - Enables the microcontroller to be programmed via In Circuit Serial Programming (ICSP). This is basically a simple 6-pin connection that is an alternative to the USB. Think of the USB as a grand entrance to a building and the ICSP as a backdoor.
- Microcontroller Circuit - Contains the actual microcontroller and its crystal (a separate component which the microcontroller uses to measure time).
- LED - All Arduino boards come with a controllable on-board LED.
|An Arduino Uno being programmed via ICSP|
|Hydra's Custom PCB|