Would it be possible to extend OpenSprinkler to monitor temperature readings from sensors and turn sprinklers on based on that information? In addition to using it in the regular daily programming, I would like to also use it to prevent frost from ruining the garden by turning on the sprinklers when the temperature goes below a certain degree.
You could also use something like a Hunter Freeze-click and wire it up to the Rain Sense port. If the temperature gets too low then this sensor will activate your Rain Delay. With that said, you could also wire a Wind-Click sensor to stop watering if the wind speed is too high.
On the FAQ page, I read this: “Also, if not using the RFM12B transceiver, digital pins D2 and D10 are free in all hardware versions.” Does the RFM12B transceiver come with the standard purchase of OpenSprinkler, or do I have to buy the pair listed on the website?
The idea would then be that if I have a wireless temperature sensor (such as this one: http://altelectronics.co.uk/shop/arduino/temperature-humidity-sensor-with-enclosure/prod_80.html), I would just have to modify the source code to receive this data.
RFM12B is not included in the package and you have to purchase it separately. We used to carry them in store but they are now replaced by the simpler, cheaper and more common 433MHz and 315MHz RF transmitter / receiver. You can purchase RFM12B from a variety of places such as SparkFun, Modern Device etc. Note that only OpenSprinkler DIY 1.42u has PCB pads designed to fit RFM12B — the newer version of OpenSprinkler 2.0 does not have PCB pads for it (although it’s still possible to connect it manually to the SPI bus).