I know, this project has been rather quiescent.

One unknown was whether the trick of using a charge pump to supply the LCD contrast voltage would work or not. The basic idea is not completely unknown, but I had never done it.

To recall, the XMega controller at the heart of this project only works at 3.3 volts, and the LCD spec says it requires 5 volts. If you didn't use this trick, then ostensibly you'd need half a dozen bidirectional level shifters to bridge the gap. In fact, the LCD controller chip in the module works just fine at 3.3 volts, and the LCD simply requires the contrast voltage to be around 4.5 volts lower than Vcc. So using an inverting charge pump to make -3.3 volts would allow the contrast voltage to range between 3.3 and 6.6 volts lower than Vcc.

Well, I built up a Toast-R-Reflow II controller with a 3.3 volt supply for the entire system (it had a 3.3v thermocouple interface chip, so it was a good candidate), and sure enough, the LCD works just fine.

Now I need to port/replace the Arduino LiquidCrystal library to straight AVR libc.