Nixie Clock 2
From neurotica.com
I built this clock in 2007 as a Christmas gift for someone. It uses Nixie tubes (a gas-discharge display device from the 1950s) and is built around a classic 8751 microcontroller. It runs from a 12V "wall wart" power supply and uses a step-up switching converter to generate 170V to drive the Nixie tubes. It's built into a "shadow box" picture frame that I purchased at Ikea. These frames make excellent chassis for home-brewed electronic widgets which are intended to be mounted on a wall or stand up on a desk.
The microcontroller is clocked at 11.0592MHz, though a much lower clock rate would've been fine...I just have a big bag of 11.0592MHz crystals so I tend to use those first. The RTC functionality is built around a Philips PCF8583 chip. The microcontroller communicates with it via I2C, which is bit-banged in firmware. The hour & minute Nixie tubes are IN-14s, the seconds tubes are tiny IN-17s. These are both late-model Russian tubes. The switching converter is built around an MC34063 DC-DC converter controller chip. The tubes are 3x2 multiplexed using MPSA92 HV PNP transistors to switch the anodes. The firmware is written in a mix of C (using the SDCC compiler) and assembly language.
The step-up switching converter is a very simple circuit based around an MC34063 chip. The circuit design is derived from similar circuits in the MC34063 application notes. While some component types are critical, such as the use of low-ESR input and output capacitors and a fast-recovery catch diode, all components are inexpensive and easily obtained. I encourage you to use this circuit in your own designs. The schematic is available on this page.
