I recently discovered Arduino (http://arduino.cc), which is a simple microcontroller with a standard PCB board layout, where assembled boards are sold cheaply. The Arduino Uno seems like a good one to use for prototypes, as all the I/O pins are taken out to headers that you can attach jumper wires to easily. For 'production' versions though, the Arduino Nano seems like a better option, as it is much smaller, and you can solder connections directly onto the board rather than using jumpers etc. I bought a few of these (or at least clones of them) very cheap (~£11 each) off Ebay.
You can download a simple development environment where you can write the code for the boards in C/C++, compile it, and load it onto the board via USB - seems to work very well.
By far the best feature of Arduino though is the user contributed libraries - there are libraries for accessing one-wire devices, LCD displays etc., so you do not have to start from scratch for each project, which makes development much, much quicker.
So, I am starting to think of all of those 'I could make one of those, but it is a bit of a waste to use a full-blown computer for it' projects. The ones I am starting on are:
- Solar Thermal Monitor (Power Meter for water heater solar panel) - I have a first version working - see the solThMon directory in my Github repository. A bit more description is provided in the github wiki.
- Alternative Weather Station Receiver - the idea is to use a simple 433MHz radio receiver to read the signals from our weather station, so we do not need the big LCD display that came with it (no progress yet, but I have the hardware for it...).
To give an idea of what these things look like, here is a picture: