IN-8 single nixie tube clock

After receiving one IN-8 tube from a friend (thanks), I decided to build myself a clock. This clock is more an ornament than a useful machine because it consists of just one digit (tube) so it displays current time every minute for three times. It is built inside of an old wooden box and it's powered from a 7V DC wall adapter. Under a nixie tube there is a very bright green LED which makes everything look more beautiful. When time is not displayed, this LED blinks with 1 second period (seconds counter).

To power-up a nixie, some 170V DC is required, which means that there is a step-up converter on board with MC34063A IC.

You can download the project files at the bottom of this page by clicking on red "download" button.

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On the back there is a small push-button to set and display current time on demand.

backside
Back side

opensmall
Inside of a box

Setting up the time
To set the time press the button and power-up the clock. This will enter the programming mode. Now 00, 00, 00,... will be displayed. Press and hold the button until hours are set. Release the button to switch to minutes. Now do the same thing with the minutes and that's it! After programming, the current time will be displayed.

Setting the time to 17:03

Timekeeping and measuring
Inside of this box there is a 3V Lithium battery (CR2032) that keeps the PIC microcontroller running even when the clock is turned off (the wall adapter). This is very convenient because after powering it up again, we don't need to set the time - again. If a button is pressed during a power-down, nothing will happen. With PIC microcontroller I used a "watch" crystal at 32,768kHz. It's value is pretty cool and now we will see why. PIC16F84 has internal TMR0 counter that increments itself no matter what the PIC is doing at the moment. Think of it as a threaded sub-program. This counter can generate an interrupt when it's value overflows from 255->0. We can also prescale this counter to slow it down a bit so we can make it generate an interrupt on every 2, 4, 8, 16, 32, 64, 128 or 256 overflows. So, when we finally connect our 32,768kHz crystal on PIC microcontroller, we should also know that the speed it runs at is divided by 4 and this characteristic is only found with PIC microcontrollers. This all means that our PIC runs at 8,192kHz which tells us that TMR0 will overflow 32 times per second. Now when we prescale it by 32 it means that it will overflow once per second and generate us an interrupt. This we can use as a very precise time measurement. Anyway, source code is available for download so you can poke around.

Time display request at 16:57

23:00

Note: PCB is double-sided.

pcbtop
Front side
pcbbottom
Back side