Monday, March 30, 2015

Designing a hydroponic automation controller with Wattmon part 1

I have been playing with hydroponic systems since several months and have found that it requires regular checking to ensure that it does not run dry and that nutrients and pH are within acceptable limits.  I have been planning to use a Wattmon to do this but only just got started.  The idea is to first monitor the system and send email alerts when user intervention is required, and at a later stage add automation to keep everything healthy.
There are many parameters that affect a hydroponic system, but the most important ones are pH, EC and water temperature.  The pH needs to be in an optimal range (usually between 5.8 and 6.5) in order to ensure proper nutrient uptake by plant roots.  The electrical conductivity (directly proportional to TDS or total dissolved solids) indicates the strength of the solution in the water.  This will vary as plants absorb nutrients or water is added.  An EC of 1.5 to 2 uS is quite commonly used.  This translated to between 750 and 1000 ppm of dissolved solids.  Finally, water temperature affects the growth of plants.  Cool weather plants suffer when the water temperature is high.  The available oxygen decreases as water temperature increases too.
The WattmonPRO has several IO lines which will be used for this project.  Two analog inputs will be used to measure pH and TDS respectively.  The onewire port will be connected to a waterproof onewire sensor.  Two digital inputs will be connected to float sensors in the nutrient tank to monitor water levels. An auto/manual switch could be connected to enable a manual servicing.
Eventually, 4 digital outputs will be connected in the following manner: 1 will open a solenoid to fill the tank with water. Three outputs will connect to small dosing pumps for stock solution A and B, and acid to regulate the pH. The 5th output could be used to control a pump or other solenoid if required.
PH is sensed using a pH probe and an interface module that generates a 0-5v signal. This is then calibrated in the Wattmon and the pH is displayed on the dashboard.
The TDS module generates a sine wave and passes a small current through probes in the water.  The amount of current that flows directly correlates to the amount of salts.  This is amplified to a 0-3.3v output and read by the Wattmon.
These values are currently being logged, and the next step is to add some automation based on the values, in a small test tank in my office before taking it to the live setup.

1 comment: