Original Design by Markus Frejek
The software (hex-file) can be downloaded from the above website.
Schematics rev B
Schematics (with error)
In the first version of the schematics (no revision) The values of the resistors R9 and R10 were confused, rendering the reading of the battery voltage inoperable. Low battery is not detected. Rev B of the schematics corrects this and has some other cleanup.