I've built a wireless temperature monitor with the following features:
Very low-power (7uA) sleep mode
Dual 1-wire dallas temperature sensor inputs, to measure two temperature sensors at the same time.
A 2-line LCD display that displays the current measurement for 15 seconds when a button is pushed.
2xAA battery supply, with charge pump to power the LCD, temperature sensors and 433Mhz wireless module.
Uses VirtualWire to transmit the data to an MSP430-powered receiver module.
This is all currently sitting outside, and the indoor rx unit is uploading the measured temperatures as well as the battery voltage to Cosm.
I've attached to this post the eagle files for the outdoor unit, and the veroboard layout for the same. I'll upload some photos also, and details of the indoor unit and the python script that uploads the data to cosm. The indoor unit is currently sitting on a breadboard, not in a nice project box, but its time will come
I've hacked the VirtualWire library to bits, leaving only the transmitting portion of the code. This was so that I could understand it, and so that I could have it running at a lower timer speed for (very slightly) lower power.
There's a few things in the schematic that might not really be necessary. I've used two fets to switch off the radio and the lcd/sensor separately, because I was under the impression that the radio transmitted the whole time while powered on. I now realise that it only transmits when the data pin is high, so I could have saved myself a component there. Also I'm using a whole hex level shifter IC just for the one input into the radio, because the other shifter's lines are all used up by the LCD. This also isn't necessary, since a singe fet would have done the job if I'd inverted the output of VirtualWire in software.
But in any case, it all works, and seems (so far) fairly reliable. There are some spurious readings that I accidentally uploaded to cosm while working on the receiver end, but other than that I'm pretty happy. What I'm really quite interested in is how the battery voltage is going to change over the coming few years.
Please feel free to use any of the code that I've uploaded, but be aware that in the words of some other forum poster somewhere, it's not supposed to be pretty - it's just supposed to work!