By: Sebastian Moruszewicz, Jacob Tentis, and Mike Lee

Statement of Purpose

Our project is a numeric character display that utilizes cold cathode tubes, colloquially known as nixie tubes, in order to display customizable data streams from the internet. Although there are multiple designs that incorporate nixie tube displays, our solution will differ by polling information from the internet rather than exclusively displaying local data like time or date.

Background Research

General Tube Characteristics:

Cold cathode tubes are neon filled glass tubes used for displaying numbers and symbols. They rely on a metallic grid for a common anode with numeral cathodes placed behind it, and unlike other vacuum tubes, they do not require the cathode to be heated to high temperature in order to function. Cold cathode tubes come in multiple standards with set sizes and electrical connections, these include IN-11, IN-12, and IN-13. Each tube has pins for every digit, the anode grid, as well as pins for any additional indicator cathodes. 

Electrical Driving Characteristics:

Nixie tubes require a high voltage rail at approximately 200 Volts DC in order to energize the neon gas contained within and illuminate the selected digit. Although they require high voltages to operate, nixies tubes have a low current draw, and as such can be driven from common voltage levels using a boost converter. Additionally, due to these tubes not requiring high temperatures to operate, they do not require that a voltage be applied to a constant starter element to preheat the tube.

Design Details

Block Diagram:

System Overview:

Our nixie tube driving solution begins with an ESP-32 which is responsible for connecting to the internet, pulling data, and interfacing with the driver modules. The driver modules consist of constant current led drivers paired with a transistor on each cathode, allowing us not only to witch which digit or digits are at a given time per tube, but also allows us to pulse width modulate our transistor base voltage in order to dim the tubes. These driver modules are connected via SPI bus, and depending on MCU internal peripherals may be separated into two busses,  thus allowing for high speed communications and implementing visually appealing pwm curves across all tubes. Powering the high voltage side we have a synchronous boost converter to minimize losses, taking a regulated low voltage DC input and boosting it to the ~200V. required to drive the nixie tubes.

Bill of Materials:

Possible Challenges

Due to the high voltage rails across the system, working on the system while live can be a concern without proper diligence. Additionally, if the boost converter IC were to fail it is possible that a runaway condition could occur and drive the capacitor beyond its maximum rated voltage, and subsequently explode. Finally, it is our goal for the end solution to use one pcb, and none of the members of the group are familiar with pcb design software.

References

[1]"exixe: Low-cost miniature Nixie tube driver modules", GitHub, 2017. [Online]. Available: https://github.com/dekuNukem/exixe. [Accessed: 15- Feb- 2020].

[2]"Nixie Indicator Tubes", Frank.pocnet.net. [Online]. Available: https://frank.pocnet.net/other/Burroughs/616.pdf. [Accessed: 15- Feb- 2020].

[3]"The IN-12A", Hackaday.io, 2014. [Online]. Available: https://hackaday.io/project/1940-modular-nixie-display/log/11038-the-in-12a. [Accessed: 15- Feb- 2020].