Metropolis Time

In an earlier rambling, I introduced the Metropolis Oscilloclock, themed after the classic 1927 science fiction movie. The clock seems to have garnered some attention, and thanks to the kind folks over at Hackaday, I now have two additional facts to relate:

  1. The “Maria” robot in Metropolis inspired the design for C-3PO in Star Wars!
  2. Some folks have considered the Workers’ clock to be Decimal !

The first point stands without dispute, but let’s take a closer look at this “Decimal” aspect, as I’d never considered it before.

Decimal Time vs. Metropolis Time

Below is what got folks interested – the 10 hour clock face. The Masters used this to dupe the Workers into believing they were working short shifts, when in fact they were slaving away for a full 12 hours. Ingenious!

But this is not Decimal Time, where time is divided into units that are purely decimally related. Yes, there are 10 hours on the face, but there are 20 hours per day, and 60 minutes to the hour. And, if you bother to count the dots around the edge, you can see there are 72 seconds per minute. None of these are decimally related.

Speaking of decimal time, I fondly remember a Metric Clock article in the April 1987 edition of Electronics Australia. Being but a wee lad at the time, I was gullible enough to believe that true Decimal Time was going to be introduced in Australia imminently. I ‘convinced’ my father (he led me on) that it was really happening, and I was just about to purchase the kit to build my own Metric Clock… when in the following month’s edition, the magazine came clean that it was actually an April Fool’s joke!

But enough fooling around – let’s now take a closer look at the Oscilloclock implementation of Metropolis Time…

Metropolis Time vs. Regular Time

The two clocks in Metropolis differ only in one way: the length of an ‘hour’. This is easy to grasp, since there are 20 hours per day in one, versus 24 hours per day in the other.

But from here, Metropolis messes with your mind! Below are some revelations that [Andrew] and I battled over numerous e-mails to come to terms with:

  • The hour hands on the 10h face and the 12h face must always be exactly aligned (they must go around at the same speed).
  • Since an M-time hour is 20% longer, the minute hand must go around slower.
  • To make the M-time minute hand go around slower, the second hand must also go around slower.

Even if this makes sense so far, the crunch comes when you think about how to implement it. If it were a physical clock, the tick speed could be slowed and the gears could be modified to make the seconds and minutes go slower but the hour hand itself move at the same speed. Easy!

But it’s not a physical clock, and in the current Control Board design, the tick speed is NOT readily adjustable as it is derived from the MCU clock, which all the critical display routines are optimised around. So essentially, the length of a second cannot be changed.

Without changing the length of a second, how can we make the minute hand go around 20% slower? Well, there are only two options:

  1. Have 72 seconds per minute, with 60 minutes per hour
  2. Have 60 seconds per minute, with 72 minutes per hour

We decided on the first option, and you can see from the video below that the second hand indeed moves through 360 degrees in 72 steps (actually half that, since there is a half-tick).

An interesting tweak here is the shape of the hands. Note that they have triangular outlines, to more accurately mimic the hands in the film. But computing the angles and projecting these outlined hands using Circle Graphics was a true challenge – especially as the current Oscilloclock firmware is written 100% in PIC18F assembly code! Assembly is great for optimizing timing, but with no maths related processor instructions or functions to leverage, this feature was a huge effort…

Why assembly code? Just because I can!

Digital Metropolis Time

Everything was now all fine and dandy for the analogue 10h clock face, but what about all those nice digital faces that are stock standard in every Oscilloclock? Could I make Metropolis Time make sense in a digital format as well?

Of course! Except there was one hitch. Since we have 72 seconds per minute, the clock would show times like 09:16:65. This would look odd. Andrew wanted to keep the seconds in the range 0-59, like in a normal clock. Something would have to give… but what?

The answer was to simply ‘ignore’ one second in every six; i.e. the 5th second shows for 2 seconds before incrementing. This is easiest illustrated with another video (note what happens at the 10:57:55 mark):

But easiest of all is to see this in Excel. The duplicate second is highlighted:

Switching between Metropolis and Regular Time

Now, let’s face it: Metropolis time is really not very useful in day-to-day life; not for us Masters. Andrew wanted to be able to revert all faces at will to show Regular time instead of Metropolis time (except the 10h analogue clock face).

This was duly implemented during production of the 2nd Metropolis Oscilloclock – which will be presented in an upcoming post. Stay tuned!

If, like me, you are hopeless at simple time zone conversions but you’ve actually managed to fully get your head around the above, Congratulations! Stay tuned for more posts in the Metropolis series.

Timedrops in Spring

Spring… a beautiful time of year! I particularly enjoy the warm rains, with the soothing effects of raindrops pit-pattering into puddles outside my window.

But no longer do I need to look outside! Inspired by a recent post on Hackaday, a suggestion from [A-Nonamus] in the neonixie-l group, and by Spring itself, I can now enjoy Timedrops on my Oscilloclocks:

See this in HD, and find more exciting videos on my YouTube channel
Music credits: Space Bazooka by Kirkoid (c) 2013 Licensed under a Creative Commons Attribution (3.0) license.


The current Oscilloclock firmware is written entirely in PIC 18F Assembly. The Timedrops feature leverages a Sprite Engine module, first developed for Halloween Seasonal Treats and later utilized in the Santa’s sleigh feature.

A sprite engine

A sprite engine

To display Timedrops, the sprite engine is initialized with 10 sprites – 4 digits for hours and minutes, a colon, and 5 ellipses as ‘ripples’. The 5 characters are set at the top of the screen with a randomized negative velocity. When a character reaches the bottom boundary, the sprite engine’s default explode sequence is started, and the associated ripple sprite is made visible and set to expand. When the explosion sequence for a character sprite is complete, the sprite is reset at the top of the screen.

Looking for the source code? Sorry – refactoring is still under way, and the latest revision with the Timedrops feature will be uploaded in the near future.

Santa in your Clock!

The world-renowned Santa Claus. How does he get in your house to deliver presents? Does he go down the chimney (if you have one)? Does he shrink and squeeze under your door? Of course not! What silly ideas.

Santa simply converts himself into pure energy and beams in!! I’ve seen this glorious event myself, and now you can too – with the latest Seasonal Treats enhancement from

Beam me in, Santa!

Beam me in, Santa!

Not only can you watch Santa on his travels, but you can even control where he drops his presents! Can YOU help him deliver the gifts?

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Do chips have bugs?

There are probably many people who think that microcontrollers are bug-free. After all, they are glorified integrated circuits; a hard-wired jumble of infinitesimal transistor logic gates. There should be no unexpected behavior, as long as you operate the device within the rated voltage and temperature parameters….


What we tend to forget from our CPU architecture classes is that a CPU actually has a program inside. Known as microcode, its primary function is to interpret each instruction into the right electrical signals to drive the various parts of the CPU. For example, an addlw 0x7F instruction might involve directing the ALU’s input to the next word in program memory (0x7F), and then telling the ALU to add it to WREG, with output set back in WREG. The microcode for addwf MyVar would be different again; it needs to get a value in RAM, and set the result back there too.

Well, where there is a program, there will definitely be bugs.

My first experience with a microcontroller bug cost me several weekends of frustration, fretting, and frantic but fruitless rework. Here’s how it happened:

Oscilloclock Gone Wild

It was the early days of the Prototype, And things were looking great! My dream was coming to fruition! Except… every once in a while, the clock would go absolutely berserk. Seemingly at random, it would start displaying crazy, meaningless images, and controls would cease to function. Sometimes it would recover; other times, it would exhibit brain death – requiring a hard reset.

April Fool's? No - it's a PIC bug!

April Fool’s? No – it’s a PIC bug!

No amount of testing or experimentation could tell me what the problem was. I rewrote huge blocks of code. I removed massive chunks to simplify the code. I drank more and more coffee. Sleepless nights and grumpy days ensued, wasting my precious youth!

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Font & Figure Creator!

Those of you who own, or are building, an Oscilloclock may have realized how tedious it is to create a new character or drawing. My little Casper (October, Seasonal Treats post) required a grueling 5 hours to get him looking good!

Casper - as drawn by my son (L) and then the Oscilloclock (R)

Casper – as drawn by my son (L) and then the Oscilloclock (R)

The current method – Painful

I have another blog post series in progress describing the theory behind Circle Graphics figure display, so I won’t elaborate on details, but the current process of getting a figure from paper to screen is very much manual:

  1. Roughly sketch out your figure on graph paper.
  2. Split out your lines and curves into blanked circle and line segments.
  3. For each segment, roughly ascertain the circle’s radius (width and height) and centre coordinates.
  4. Type the numbers into the code file, in PIC assembly language syntax.
  5. Build the code and Program the PIC.

NO.The figure looks NOTHING like you expect. The size is wrong. The edges don’t meet up. The curvature is out. The thing is upside down. All of the above!

  • Repeat steps 3, 4, 5 for several hours. Drink coffee. Redraw and repeat for yet another few hours.

  • Finally – Celebrate the birth of a new figure!

The Easier Way

The new Oscilloclock Figure Creator utility allows you to easily create and modify font characters, graphic images, and sprites – interactively.

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Circle Graphics – Lissajous figures

By the time you read this post, you must have seen the term “Circle Graphics” in a thousand places across the site.

In fact, “Circle Graphics” is not an official term – I just use it to describe how shapes are drawn on these clocks:

Everything you see on this screen is made up of CIRCLES! Blank out part of a circle and you get an arc. Squish an arc and you get a line. This clock simply draws circles, lines, and arcs of different sizes at various points around the screen. It does it quickly. And it does it very, very well!

The effect of using circles is beautiful – shapes are smooth and precise, with no jagged edges or pixelation.

Beautiful circles with no jagged edges

Making “perfect” circles

I carry on as if it were some incredible new concept or discovery, like the Higgs boson. But in fact, the analog technique of constructing perfect circles, ovals, and lines on a CRT is very, very old. These figures are really part of a class of shapes called Lissajous Figures.

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BOO! proudly presents a new feature – Seasonal Treats !

This month, the ghosts come out of the attic and merge with the electron stream, leaving their telltale prints in the phosphor… but if you get too scared? Just push the button and blow them up!

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