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Sunday, November 30th, 2014 03:40 pm
As I mentioned earlier, I'm working on expanding the Sprinklers smart controller to make it support a network of wireless remote stations. Each station can control a set of watering zones, and it can also collect data from environmental sensors - temperature, humidity, air pressure, soil moisture. Remote station can also collect water flow data.

Over the last month I finished design of the remote station, built a prototype device, and now I'm finishing up the firmware for it. This post is an overview of the Remote station.

Remote station is built on Arduino - powerful yet inexpensive platform for DIY projects. Bit attraction point of Arduino in this context is the availability of all sorts of sensors, RF modules and other add-on hardware, and associated libraries. Also Arduino has low power consumption, and is suitable for even battery-powered devices (although right now this part is not important for my project).

My remote station consists of an Arduino MCU, local LCD and buttons (to allow limited local control), relays for controlling irrigation zones, few sensors, and RF module for communication with the Master station. I'm using excellent RBoard MCU from iteadstudio.com, it includes AtMega328P (Arduino Uno-level hardware), 4 electromechanical relays, SD card slot, and Xbee and nrf24l01 modules interfaces. RBoard is just more convenient (and more compact) for my purposes.

LCD is C0220BIZ-FS(RGB)-FBW-3VM display from Jameco, it provides 20x2 character mode with RGB back light, it connects via I2C interface and runs on 3.3V - perfect fit for RBoard.

As the RF interface I'm using Xbee Pro 900MHz modules - I need sufficient range and power to be able to reach far end of my property in adverse link conditions - foliage, rain (you still need to get sensor readings!), devices location in a wet box near the ground etc. Unfortunately regular inexpensive modules like nrf24l01 cannot do it, but Xbee Pro 900 can. Xbee modules are more expensive, but for a few devices in a home DIY project it does not really matter that much. Good thing is that it is possible to use nrf24l01 modules instead of Xbee, I might experiment with it later.

Remote station supports both regular 24VAC valves, and Orbit DC valves. 24VAC valves are connected directly to control relays, while Orbit DC valves are connected via my voltage converter module (simple circuit that produces DC pulses on On and Off).

Remote station is powered from a standard 24VAC line. It is actually possible to use any suitable power sources (e.g. 12VAC or 24V DC), main constrain is the need to have sufficient voltage to drive irrigation valves.

Remote station is powered by a small rectifier/buck converter module. I could've build one, but there was a suitable module available on Amazon, and I went an easy route:-)


RBoard




The station is assembled in a clear plastic 6"x4" box. The box is reasonably weather-sealed, although I would not risk putting it under the rain - I had to drill few holes for buttons and LCD mounting screws, and it is hard to make it truly watertight.

All together it looks like this:



The empty space at the bottom of the box is the space for the Orbit DC voltage converter - it is not required for 24VAC valves but is necessary for driving Orbit DC valves.

I have baseline software up and running, except Xbee communication part. That code needs more work, and it requires also updates to the Master station (to add Remote stations support).

Next steps - hopefully I will have more time available before the end of this year to finish up the code and to get RF hookup going. Once it is done - it will be possible to start making 3-4 stations to get ready for the next irrigation season.

Another thing I'm considering to try - moving Master controller to a small tablet like HP Stream 7. It has very nice 7" screen, and pretty powerful hardware - all for $99 (!). Initially I was thinking about moving it to RPi, but Stream 7 is a way better machine - it has more resources, nice 7" screen, WiFi, decent storage, even backup battery. And it is running full Windows, which makes development a lot easier.