6 digit Nixie Clock

##Motivation

Steins;Gate's Divergence meter

This project is based on this instructable by Andrea Biffi with modifications.

##Project structure

• clock_firmware - firmware for our display(powered by Arduino Nano)
• esp8266_firmware - firmware for our ESP01 that handles NTP sync
• src - PCB design and schematics in DipTrace format
• tools - binaries for flashing the ESP01 WiFi module
• docs - various PDF datasheets for our components

##BOM Summary Main components

• IN4 Nixie tubes
• SN74141 BCD decoder IC
• Arduino Nano v3
• ESP01 esp8266 WiFi module

The BCD decoder IC and Nixie tubes is hard to obtain, so far they're only available on ebay and most of them are NOS(new old stock)

Check the schematics for the rest of the passives

##Theory of operation

###Display Unlike LED segment displays, Nixie tubes requires high voltage DC to illuminate. This poses a challenge as the decoder IC has to accommodate for this requirement, luckily, Texas Instrument has a jellybean solution that we can use. For cost considerations, we multiplex the tubes with 12 high power transistors.

###Architecture Arduino Nano drives all the displays. Nixie tubes are multiplexed and given a 2ms illumination interval. For 6 displays, this is equivalent to a refresh rate of ~83Hz. Time keeping is also done with the Nano, a basic serial API is exposed:

(Commands must be the start of line and prefixed with "@")

h<string>:<string> - heartbeat, returns the given string
s <long>:<bool> - set current time in millisecond
c:<long>- returns current time in milliseconds
r:<bool> - invalidate display now
t <int>:<bool> - display invalidate interval, default 1s (1000ms)
m <[c+(H|M|S|s)]|[s]>:<bool>- display mode for each display

ESP01 handles time synchronization via NTP through WiFi. The module is programmed to sync every hour with a predefined NTP server.

Nano and ESP01 communicates via serial. A software serial interface is also exposed on the Nano for debugging.

###Software

• Display firmware is written in C++ and compiled using the gcc-avr toolchain
• esp8266 firmware is written in lua running on top of the NodeMCU platform

##Firmware build instruction

###Clock firmware

1. Download and setup Arduino software
2. Navigate into clock_firmware, open the clock_firmware.ino file
3. Connect your Arduino Nano to your computer
4. Verify and flash

ESP8266 firmware

1. Download the latest NodeMCU firmware
2. Connect your ESP01 via USB TTL adapter
3. Flash NodeMCU firmware using the Flasher tool in the tools directory
4. Start up ESPlorer(also located in tools)
5. Load both init.lua and ntp.lua files

##NTP sync

##Photos

Completed clock Board wiring Case prototype with PCB installed Back side of PCB Testing (@9V 121mA) PCB exposed on the back HVDC prototype PCB Nixie display board socket assembly Display board assembly Display board close up All PCB All PCB close up HVDC testing(300VDC)