I've two offices, so I'm requiring two of this timers.
The second one I built with a three-digit display and auto-power-down and start with a push-button.
This thing consumes in operation about 20mA, which is a real lot for so few functionality, but most of the power goes into the display. I was looking for a simple LCD on ebay, but it seems that most of the LCD 7-segment display have only one common and one pin for every single segment instead of one common per digit. These are too many pins for the 2553 and I didn't want to put an additional LCD controller on the board.
However, when the thing goes in LPM4, it only consumes about 0,1uA, as it is written in the datasheet. Very important to achieve this low power consumption: an input pin requires more power than an output pin put into the right level. And of course the reference generator of the ADC needs to be shutdown.
The sources are still available here https://bitbucket.org/wollud1969/teathermotimer https://gitlab.com/wolutator/TeaThermoTimer/tree/SecondEdition, look for the branch SecondEdition.
The schematic is more or less the same, just on digit display more and a reset push-button.
