Nerding out with the Irrigation System

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Constantin

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This summer, my irrigation system experienced a triple failure, resulting in a parched garden. Since a simple solution would be logical, I opted for something more complicated instead. Here is the first mockup of a OSH Park Teensy 3.1 being sent to the purgatory, i.e. monitoring 20 24VAC inputs for activity. Each of those inputs is for the various zone valves, float switches, etc. that make up the irrigation system.

IMG_6738.jpg

The blocks below use a LTV844 AC Optoisolator that uses a common ground for all the 24VAC signals and a ceramic cap/resistor combination to limit current through the LEDs inside the opto-isolators. 100V, 2.2uF, XR5 or XR7 ceramic caps are not easy to find in small sizes! The opto-isolators are removable (DIL sockets) in case I manage to screw up.

Additionally, the Teensy will monitor differential water pressure on the filtration system, ticks on the water meter, water level inside the cistern, outdoor temperature and humidity, and display all that on a external 20x4 LCD display. I also planned ahead by allowing the system to communicate to the great indoors via RS485 and to feature a simple SSR alarm output. The Teensy rig shown in the picture is just the first mockup. The 1.1 revision of this board uses so many pins that only D33, A14, and D13 were left alone (D13 makes for a good "I'm alive!" signal while D33 has been excommunicated).

OSH Park just sent 1.1 to the fab, and OSH Stencils is making the stencils for the next revision. In the meantime, I am rewiring the irrigation system from the current contractor special (aka rat nest) to something that is more easily trouble-shot. Once that is complete and the monitoring is shown to work, I will initiate the next phase of work, as I want to be able to detect issues with the irrigation system sooner in the future, i.e. for example note that the water filter is bogging down and initiate a backflush while the common return for the zone valves is disconnected (makes for a better backflush).

Incidentally, I designed this board to also help monitor my HVAC system. Stay tuned, this will be featured in a follow-up post.
 
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It's a pair of eBay units meant for automotive purposes. 5vdc supply and a 0.5-4.5vdc ratio metric output. 0-100 psi range, Stainless body, 1/4" NPT thread, about $20 ea. I can send you the link, if you like.

I used a voltage divider + capacitor to bring the sensor output voltage down to teensy levels. The differential in output should be good enough for use.
 
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To detect the delta-P between the outlet and the inlet to the filter assembly? What I mean to say is reading both sensors simultaneously (adc0 and adc1) and then observing the differential pressure from those two readings. Apologies for bad wording above, will correct.
 
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