EEVblog® Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: burko on December 10, 2013, 12:22:33 pm
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Just finished my irrigation controller design, build, and install. Take a look at www.burkotronics.com.au (http://www.burkotronics.com.au)
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Looks good. Our company Alex-Tronix manufactures agricultural irrigation controllers. Ironically i am playing with that same SMPS module now for one of my next designs. The price for that module is less than my BOM in 1K quantities! (Shhhhhh.... Its not a real national part on there. ;-) Looks good. Whats the temperature sensor for? Freeze control? If you look up our patents you will see everything you need to make it self adjust the watering duration on a daily basis based on temperature alone. If you want I will dig up the numbers and you can get the math off off the document from the US PTO website.
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You may want to put mov's of lets say 47 volts across the solenoid outputs. Just another observation. Oh, and don't forget the freewheeling diodes on the relay coils. Forgive me if you already have those.
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Thanks for your comments.
I did think about frost detection with the temperature sensor but I was also curious how hot and cold the board is getting in the solenoid valve box. I don't think temperature alone will give enough information for watering. During the summer it can be 35C here and have a thunderstorm in the afternoon with lots if rain. I have a weather station that the irrigation controller can access through the raspberry pi that will tell how much rain if any has been received. Perhaps this in combination with what you suggest would provide a good solution.
As for freewheeling diodes the solenoids operate on 24VAC, therefore diodes across the solenoid would short for 180deg of the waveform.
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The diodes are on the relay coils. The mov's are across the solenoids. You will find a valve box in spring and summer tracks ambient temperature rather well. A small correction factor is usually all that is required. In winter things change a bit.