Yet Another Nixie Clock

After two years of stalling, I finally finished my first nixie clock. It uses B-5092 nixies from an old TSI rack-mount event counter. The heart is an Atmel AT90S1200 microcontroller, with the nixies driven by TI 75468 HV buffer chips via a shift register. This version uses a transformerless voltage doubler power supply and as such is suitable only for laboratory use. Software for the microcontroller was written in assembly languge using avr-gcc (this particular chip has no RAM and so is not supported by the gcc C compiler).

This was really intended to be a kitchen timer, and when I get around to it I'll build another one and put it in a kid-proof box with a beeper (and transformer-isolated supply!) and write some new software.

Meanwhile here's the clock on the wall of my office. Setting is currently accomplished by shorting together various pins on a header on the PCB. I'm making a plexiglas cover which will have two setting switches (and keep prying fingers out).

Large (136K)

Large (208K)

Large (152K)

WARNING! Hazardous Voltages Used! If you try to build one of these, use an isolation transformer, and do not touch any part of the circuit while it is powered.

Here's the basic documentation. The PCBs were "mini-boards" from expresspcb.com (three for $59 including shipping). All other parts except nixies were from Digi-Key.

timer_sch.pdf	Schematic
timer_pcb.pdf	PCB Layout
timer_1.zip	Layout/schematic files for ExpressPCB
clock_sw.zip	Software (requires avr-gcc)

Construction Hints:

• the Nixie symbols on the schematic are used for connectors, and on two of them I only hooked up the anodes 0-5 (I originally designed the circuit for a kitchen timer which would display 59:59 maximum). Of course the resistor is actually wired to the cathode.
• I used the TI drivers (SN75468N). The ExpressPCB library had ULN2003 symbols which are pin compatible so I used them. As I recall ULN2003 are rated for 50V while the TI parts are (I think) rated for 90V.
• R1 (10k) should be 2W also to be safe.
• There is one error on my PCB layout. Just to the right of D4 (see the PDF layout on the web) there is a missing via (thru-hole) in the +5V line. You can see a wire patch on the close-up photo of the PCB if you look closely.