So What IS This Gadget?

The Nixie Tube Propeller Clock (NTPClock) is a unique timekeeping device that combines the vintage charm of the Nixie tube with the modern display idea utilizing the persistence of vision (a.k.a positive after-images) phenomenon. A single Nixie tube mounted on a spinning "propeller" board displays the time and date along a horizontal circular path, with multiple different scrolling or stationary patterns. The device uses the motor of an ancient 5 ¼ inch floppy disc drive as the source of regulated angular speed for the propeller; the heart of the circuitry is a PIC16F84A microcontroller.

With a later addition, the clock can now also play what is commonly referred to as 8-bit music using a small piezo speaker.

Motivation

The inescapable question is, why anybody would want to build such a thing, and the answer is this: having joined the Nixie-enthusiast NEONIXIE-L Yahoo! Group (now closed and migrated to the neonixie-l Google Group) as one of the first members, I decided to create something novel. Being a devoted clock freak myself, my obvious choice was building another clock. Nixie tube clocks had existed prior to NEONIXIE-L, so if I wanted to make a lasting contribution, I needed to up the ante. Rather quickly the propeller clock design came to mind. Propeller clocks had also existed before [since around the mid-90's], but they all used a column of LEDs as the moving display element. Building the world's first Nixie tube propeller clock was just too great of an opportunity to pass on.

Features

The clock provides a single-button interface, with different functions assigned to different button presses:

Short press: Cycle through the display patterns
Double press: Cycle through the tune options
Long press: Enter Settings Mode and navigate the clock fields

The implemented display patterns are as follows:

Stationary patterns - the digits are displayed in a fixed position in the front and back:

Time & date alternating in front & back side
Time in front, date in back
Date in front, time in back

Scrolling patterns - the digits are displayed in a scrolling (rotating) manner:

Right-scroll (continuous scrolling in anti-clockwise direction)
Left-scroll (continuous scrolling in clockwise direction)
Stand-scroll (quasi-stationary display, for tuning display timing)
MagnetoSpin (rapid anti-clockwise scroll, with slow-down for time & date in the middle)

In the tune department, the options are:

Off: When silence is gold
Chirpie: Chirping sound pattern reflecting the displayed digits
Manic Miner jingle: Hat-tip to the once popular ZX Spectrum game
Jet Set Willy jingle: Hat-tip to the other popular ZX Spectrum game
Woodycock: The well-known beautiful melody by an anonymous composer
Frequency test: Repeated sounding of the A4 (440 Hz), A5 (880 Hz) and A6 (1760 Hz) notes, for 8 seconds each
Frequency sweep: Continuous sweep of all frequencies supported by the sound engine (330 Hz to 77.7 kHz in 256 steps)

The clock also supports the different hour-display modes, selectable via a jumper on the circuit board:

12-hour mode: The jumper is removed (to disambiguate, the decimal points are flashing for PM)
24-hour mode: The jumper is in place

Press

An article about the clock was published in the February 2007 edition of the Circuit Cellar electronics magazine. It gives a detailed account of the development process and technical details of the project, featuring the v2 design prior to the addition of the piezo buzzer and the sound engine.

Click on the image above to open the article in PDF format (posted on this website with the permission of Circuit Cellar).

Project Details

The different aspects of the project are introduced in the following sections:

	Nixie & Clock History
	Mechanical Design
	Hardware
	Firmware