That generator info display project will have a box sitting outside in a shed - one that can get bloody cold during winter. LCDs are very temp-variable, and need their contrast adjusted to compensate.
I've done some digging around, and there are a couple of ways to do this. I've included a simple one below, modelled in SwitcherCAD spice. This is using a typical 10k thermistor, which ranges from around 70k at -20C to around 6k at +38C. There's a pot in there to allow you to adjust things a bit. The -ve voltage V1 is generated with an ICL7660. I have 12V available on the pcb, so V2 is at 12V. Using 5V just narrows the min Vee from -5.4V to -7.2V.
The green trace is with the pot at 470R, and the bottom dark blue one is the pot at 47k. One would adjust the pot at room temp (25C/10k) for good contrast, and as it gets colder or hotter, it *should* adjust. Getting it adjust correctly, ah, therein lies the art.
The articles I've seen talk about using a bias resistor (R3 here at 470k) equal to the thermistor resistance at room temp, in this case 10k for a 10k thermistor. But doing that really reduces the range of -ve voltage available to the LCD Vee. Hrm.
So, anyone done this before ? (Surely someone has). Does this look reasonable ?