6 digit nixie clock made from modular IN12A nixie displays.
For the time keeping it has been decided to use the M41T81 Real Time Clock (RTC) from STMicroelectronics.
Communication to the RTC is done over I2C and an important feature is the alarm capability. It was easy to develop the following schematic from the datasheet.
From there we were able to etch a break-out board and start testing it using a PIC microcontroller development board.
Above is top side view without CR2032 battery installed and below is the bottom side view.
Useful table outlining the pin out for the board.
Thus, we have been able to communicate with device, set the time and read the time.
So far the time keeping is seems accurate, however, we might need to calibrate to ensure long term accuracy.