The Nixie Tube Calculator is a fusion of vintage and modern technology. It’s intended to serve as much as a piece of art as it is to serve as a functional device. The calculator is available in a variety of kit forms, depending on how much existing components you have on hand, as well as a fully assembled version.
I’ve focused on two key concepts: hackability and modularity. Hackability is achieved by using a Raspberry Pi to serve as the ‘brain’ of the clock. The Raspberry Pi is a robust inexpensive single board computer that typically runs the Linux operating system. The calculator software is written in Python and source code will be provided.
Modularity is achieved by separating the project into several subassemblies. There are three keypads and two Nixie Displays modules. An I2C bus connects the keypads and displays, allowing you to easily reconfigure, delete, or add additional modules. The basic design could easily be extended to a 12-digit calculator, or a 4x2 keypad could be swapped with a 4x4 keypad to yield more functions.
The Nixie display modules, pictured above, feature four tubes per module. Rather than multiplexing, an individual dedicated driver chip is assigned to each tube. The drivers are then connected to I2C IO expanders, which in turn talk to the I2C bus on the Raspberry Pi. There is a provision for LED tube backlighting already designed into the driver boards, although the pictures above do not show the LED backlighting in use. It’s an option that’s there if you want it.
The keypads, pictured above, use Cherry MX blue key switches with custom printed keycaps. The Cherry MX blue is a quality key switch, often favored by gamers for its tactile feel and clicky sound. Key caps can easily be removed and replaced. If you don’t like the functions that I have chosen for the keys, you could have your own keycaps printed.
The final subassembly of the kit is the power supply board, pictured above next to the raspberry pi. A standard 12V wall wart is used to supply power to the power supply board, which features a 5V switching regulator to supply the pi and other electronics, as well as a high voltage switching power supply to power the Nixie Tubes.
The entire kit is designed using through-hole components, making it accessible to builders who do not have the complex tools or skills that are necessary to work with SMD devices. A high-quality temperature controlled soldering iron is recommended (a $90 Hakko is a good choice). Only two IO pins on the Raspberry Pi are used for the I2C communication to the modules, leaving the vast majority of IO pins available for custom hacks should you choose to do so.
The pc-boards are all professionally designed using modern CAD software, and will be professionally manufactured using a reliable board fabricator. They will feature all the amenities of modern pcboard manufacturing, such as plating of surfaces for easy soldering, solder mask, etc. Note that although only one of each pc-board is pictured above, the kits will come with two nixie display boards and two 4x4 keypads
The case is laser-cut acrylic. For the kits, it will come as a set of flat pieces that are easily assembled using 4-40 machine screw hardware. The case currently pictured in the video and screenshots is prototype quality. The final case that is included in the kits will have a full back and bottom sections to keep fingers out of the electronics.
Risks and challenges
The kit is more complex than the average Nixie clock kit, having more tubes and having the added complication and expense of the keypads. Creating a robust modular design was a challenge, and this led to the use of I2C as a bus mechanism. My personal preference is to have as many components as possible socketed so that they may be replaced in the unlikely event of a failure, so IC sockets are used for all ICs, and socket pins are used for the IN-12 tube. As the design is complete and the prototype constructed, there are few risks remaining. Most of the uncertainty relates to the supply chain – tubes have to be obtained from Eastern Europe, the acrylic needs to be laser cut, and the pcboards need to be mass produced.Learn about accountability on Kickstarter
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