So having got fed up with not knowing what the temperature in my office is, or how hot it is outside my house rather than several km away where the Bureau of Meteorology site is, and having heard about the neat little DS18S20 digital temperature sensors, built one of the “k145” kits from kitsrus.com, thinking that 4 sensors would be enough, and I’d hang one outside somewhere. The “1-Wire” bus these devices use can go quite a long way, so it seemed like a simple thing.
Then I started reading a bit about weather monitoring stuff, and I realized I was going to have to think about what might happen in the event of a lightning strike.
First I looked at isolating the 1-Wire bus back to the existing k145, but that turns out to be distinctly non-trivial; the application note on how to isolate a 1-wire bus involves a transformer, and actually results in the bus no longer being a 1-wire at the microcontroller end but having separate transmit and receive paths, which means it wouldn’t work on the existing widget.
The I bought an Arduino work-alike (an ET-Easy168 – more or less a clone of the older Nano with the ‘168 chip on it) and played around for a bit. I thought maybe I could put the microcontroller out in the garden as well, and use something like RS422 (which isn’t so hard to isolate) to communicate with it.
Then I found the cheap little 315MHz receivers and transmitters sold by Little Bird Electronics (receiver, transmitter) and was persuaded by a couple of colleagues that wireless would be worth trying. They also do bare ATmega chips with the Arduino bootloader on them, so I bought one of them planning to build my own board and keep the Easy168 as a development unit. A quick trip to Jaycar and and the order from Little Bird and I had all the bits I needed to get started.