Irrigation/Door Main

The hardware is encased in a lexan case I built. I find lexan to be fairly easy to build with and as a bonus, I can see thru it. In this case, the controller is located not too far from the wifi base station, so a miniature wifi adapter gets good enough reception. Since the case is not metal, the signal is not blocked.


Power for the beagle bone and other 5V and 3.3V derived power is from a CUI 2A potted power supply. The beagle bone generates a 3.3V rail that is used by both the display and the I2C touch controller. The irrigation zones are driven by a 25.2VAC transformer. The transformer is center tapped and used for both a 12.6VAC supply for some LED lighting in the garage and also for a 18VDC supply. Note that the garage door common and the irrigation neutral is earth grounded, so care must be taken not to have voltage across these two nodes. My original plan was to opto-isolate all signals to and from the garage door opener to ensure isolation, but was surprised to find out just how little drive the open/closed switches on the garage door opener had available. I ended up needing to add a comparator with a 50K resistor on the input to ensure the garage door opener signal was not disturbed. A quick test seemed to indicate the sense switches only had 50 microamps of drive strength. With that requirement, the 5V supply is now grounded to earth via the garage door opener, and the 25.2V domain is grounded via the common of the irrigation wiring. As long as the 25V CT node is not grounded, everything is ok.

Irrigation Solenoid control

The solenoids of the irrigation valves are controlled via the circuit here. There are 8 channels in total. Each channel is just a triac with a ZNR to protect it. The triac is driven by a GPIO output.

Door position sense

The garage door has two sensors, one to indicate the door is fully open, and one to indicate fully closed. The signal is shorted to ground when the door is in that position. The signal is about 8VDC when the switch is open. As noted before, the drive strength is very very small, less than 100 micro amps. So I used a 339 comparator with a reference of 2.5V to detect the switch status. The output of the 339 then drives an opto-isolator which drives the beagle bone GPIO input. The 339 is driven from the 5V supply and the 339 is tolerant of over-voltage inputs, which will occur in this case. See the schematic for the actual circuit.

Door activation

The garage door is easily activated by shorting the door button to ground. In order to control the duration of the pulse, a 221 one shot was used. The 221 drives a opto-isolator which acts to short the door button. See the schematic for the actual circuit.

LED light control

I have a 12VAC LED lighting system for the garage. The beagle bone powers the LEDs by driving thru an opto-isolator, that then drives a 12VDC relay that controls the 12.6VAC power. Note 2 47 ohm resistors are in series with the relay coil to reduce the voltage to the relay to about 12VDC. The rectified 12.6VAC generates around 18VDC.

Door enable

One other feature in the garage door controller is to completely disable power to the opener for vacations. A 24VDC omrom relay I had spare was used. The omron triggers reliably down to about 15VDC, so the 18VDC was more than enough to drive the relay. I did want the circuit to be "on" if for some reason the beagle bone failed, so when enabled GPIO60 is actually low, When high, it triggers the opto-isolater pulling the base of the NPN low when lets the base of the PNP float high cutting current to the relay.

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