Nixie Tube Clock
Functional Overview
Real-Time Clock
The DS3231 module is used to keep time accurate to +-2ppm.
It communicates over I2C to the MCU with readily available libraries for Arduino & different Atmel chips.
The RTC module includes a backup battery for precise time-keeping while the rest of the circuit is unpowered.
Time & date can be set easily through the MCU.
ICs
The 74HC595 shift register and the K155ID1/SN74141 are used in the clock.
The former converts a serial output to a parallel 8 bit binary number, allowing each one to control two digits.
The latter IC is a 4 bit BCD-Decimal converter intended to drive nixie tubes. It converts a 4 bit parallel input to a single output on one of 10 pins.
MCU
The code for this project is simple enough that many low power MCUs can be integrated. The requirement of 5-6 GPIO pins makes even an ATTINY85 suitable.
I2C capability and the ability to communicate with the shift registers is required.
How Do Nixie Tubes Work?
Nixie tubes are cold-cathode(with no heater element) vacuum tubes functioning similarly to neon lamps, and are designed to display information.
An evacuated chamber is filled inert gases(neon, argon, etc.) with two types of electrode - the anode and the cathode.
When a high voltage is applied to the anode and the cathode is grounded, emission of electrons from the cathode causes the gases surrounding it to glow.
In the case of the IN-4 tubes used in this project, there are 10 cathodes, each shaped for a digit 1-9.
Grounding any one cathode causes the tube to display the corresponding digit.
