Nixie Tube Clock Projects

Click Here to see my current tube collection

 

In 2003, I found this website that showed a homemade digital clock that used tubes to display the time. I immediately thought it was it was neat and wanted to build one for myself. This started my fascination with nixie tubes. At the time, I lacked the knowledge in programming but I was able to solder a kit together. I purchased my first nixie clock kit from CathodeCorner. The build was a success but now I wanted to build one from scratch. I did some more research and came across Mike's Electric Stuff. He gives plans on how to make your own nixie clock using readily available CMOS integrated circuit chips. Following his schematics, I made this clock in 2005:

Click here to see the Nixie Clock gallery

 

About two years later, I built a clock with the big IN-18 nixie tubes installed in an old power supply case. Industrial switches and led's were also added.

 

 

 

Click here for Nixie Clock related website links

What are Nixie Tubes?

Nixie tubes are filled with neon gas and contain 10 stamped plates, one for each number, 0-9. Apply +175volts DC at the anode and connect the ground to one of the 10 cathodes, and the respective number will glow orange with a slight purple hue. These displays were used before led's became cheaper. By the 1970's, led's replaced nixie tubes but led's can't replace the orange-purple glow from nixie tubes. The vintage-retro look is what i'm after. It's also neat to see the seconds change in a nixie tube. Since the stamped number plates are stacked one behind the other, the numbers appear to be moving.

I have several different styles of tubes in my collection. The most easibly obtainable (on ebay) are the Russian made tubes. I also have tubes made from Poland and the United States. Most of my tubes were bought from Russia. Click here to see my current tube collection.

 

 

Latest Nixie Clock Project

Click here to see the Nixie Clock gallery

My latest prototype nixie clock is an all digital version. After I learned assembly language for the Z80, I knew I was able to learn it for another processor. The clock is multiplexed 2x3, which means that only 2 out of the 6 tubes are lit at any given time. You don't see the flickering because it switches at approximately 200Hz as shown here. Multiplexing also reduces the parts count by 2/3. The clock is run by an Atmel atmega168 microcontroller running at 8Mhz. Timekeeping is kept by a DS1307 real time clock and a DS32Khz temperature compensated crystal oscillator. The RTC keeps time while the clock is off and the TXCO is accurate within a minute a year! Here is the frequency shown on the scope using the counter/timer function (should be 32.768Khz). Why such an odd number you ask? Because 32768 converted to hexadecimal is 8000h. It's quite simple to divide 8000h using a microcontroller to derive the needed 1Hz for timekeeping. The three anode "switches" (one for every two tubes) consists of one npn and one pnp transistor rated for 400 volts. They are essentially high voltage switches controlled by the microcontroller to turn on and off each set of two tubes in a successive order and frequency. Three tubes have their 10 cathodes connected in parallel. The selection of which cathode is grounded is done by a 74141 high voltage BCD to decimal decoder chip. This easily allows you to select a number to light up by using 4 bits from the microcontroller. One 74141 controls three tubes (two chips total). The clock is powered by a switch mode power supply shown here. Any input voltage between 9 and 14 volts AC or DC can be used. I used Mike's schematic for plans to build the power supply. It works great and provides more than enough voltage and current for 6 medium sized tubes. The 7805 supplies regulated 5v for the IC's. While the tubes are lit, the voltage remains at about 253v but by using an oscilloscope, you'll see that the voltage actually goes up to 352v for a very brief period of time. This spike doesn't affect the operation of the clock.

Time selection is done by two buttons, one selects which digit you would like to change and the other advances the number. For right now, that's all I have implemented in the software but I may add more features like the date and temperature in the future. I eventually plan to make a small production run of this clock with printed circuit boards. A schematic will be available soon.

 

 

 

Home

Contact: Tai Oliphant

Copyright © Tai Oliphant 2009