Computer Automation!
© a.k.a. MBR
This week's article focuses on the various methods and technologies involved with Hydroponic system automation.
The usual variables which are controlled through automation are light and watering cycles, ElectroConductivity (EC) which relates to nutrient concentration in solution, pH (acidity/alkalinity which will be discussed in detail in a future article) of the solution, and atmospheric temperature and humidity.
The control of light and watering cycles is easily achieved through the use of timers which can be bought at the local hardware store. Relays can be used where switching high wattages is required for lots of lights. For automation freaks, computer systems are available from http://www.x10.com and http://www.honeywell.com which can be used to control lights, pumps, etc..
The EC of the solution is best monitored using an electronic meter which measures the conductivity of the solution which rises according to concentration of ions and the units are micro-Siemens per centimeter (uS/cm). These can be purchased from many companies like http://www.hannainst.com . These meters cannot actually measure the nutrient parts per milion (ppm) because of the varying solubility of different substances, but some are calibrated to convert from EC to ppm according to the assumption that ~2uS/cm=1ppm. Computer automation for EC control can be done using simple software to control a probe wired through an analog to digital converter (A/D) and into a computer or microcontroller which can then turn on a pump to add more nutrients when required. A/D chips can be bought for ~$2 from http://www.jameco.com or http://www.dalsemi.com or http://www.microchip.com .
The pH of the solution can also be monitored using electronic devices, but it is this Editor's experience that it is more efficient to use pH indicating kits which contain Bromthymol Blue or other substances which react to turn certain colours for different pH values. These kits can be purchased in pet/aquarium/superstores. The electronic pH meters work OK, but the glass electrodes corrode as they work, and have to be replaced. Proper media should be selected to reduce the possibility of pH fluctuations. This is one reason why I and many other growers choose to use Perlite and other substances rather than Rockwool due to the fact that Perlite is pH neutral, whereas Rockwool is alkaline in nature and usually requires acid treatment.
Temperature and humidity are easily controlled using thermostats and dehumidistats connected to exhaust fans.
There are very complex computer modelling software packages being developed which will be able to predict the amounts of nutrients required by crops in recirculating systems according to environmental conditions, but these programs are in their infancy, one prototype can be found at http://res.agr.ca/harrow/software/softwa... .
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