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Handcrafted Scope Clocks with circle graphics

  • Bunker Club Clock

    Bunker Club Clock

    It’s the 1970’s. The cold war. The U.S. and Russia aim nuclear weapons at each other. How do you prepare for the worst? Why, you build a bunker, of course!

    Today, [Ian] has done just that. Not a real nuclear fallout shelter, of course, but a period-themed bar called the Bunker Club. What better way to face disaster, than over drinks with the mates!

    Ian decided to pepper his bar with vintage equipment that looked the part. But he wanted to make them truly functional, to entertain his retro-loving customers. So, he commissioned the Bunker Club VectorClock!

    Now, regular followers of the blog will easily recognize the base unit here as a Tektronix 520A Vectorscope. So far a total of four of these delightfully-lighted machines have been converted to retro Oscilloclocks – see the Gallery for other examples.

    But as always with any model, Ian wanted to make some cool customizations. Let’s look at two of them.

    1. External XY Input

    First introduced in the Metropolis Clock, this feature allows Ian to input two signals and visualize them in X-Y format on the screen. This is very, very useful for generating custom Lissajous figures externally – using either a cheap signal generator, or even an iPhone!

    Lissajous figures from an iPhone!
    Cool Lissajous figures – even from a humble iPhone! (note, this picture is of the Metropolis Clock)

    The external signals are rendered within a rectangular ‘window’, pre-configured to look nice alongside other standard parts of the Oscilloclock screens. For some screens, the window is drawn large but with a lower intensity, forming a kind of ‘watermark’. This is an awesome effect!

    2. Custom Logos

    Nearly all Oscilloclocks feature some kind of customized logo. Past examples include the customers’ business’ name, the name of the oscilloscope manufacturer, or even the name of the customer’s favourite film:

    Toshiba ST-1248D - Brass bezel
    Kikusui 537
    Metropolis Clock

    In Ian’s case, the obvious candidate was his new bar’s official logo – a very chunky-looking rocket blasting through the atmosphere!

    Further enhancements … on the way

    It seems Ian enjoyed his first clock so much, that he has commissioned a second, with a completely different physical look. Some further special effects and display animation are planned, to further enhance the nuclear theme and keep his customers happy. Stay tuned!

    Like what you see?

    Do you own a bar? Well, normally you wouldn’t want a clock in your premises, as it would help customers keep track of their time, which would be bad for business. But Oscilloclocks are so much more than timekeepers! Recent feature additions make them lots of fun to watch and fiddle with. If you have special ideas, let me know!

    (Disclaimer: Oscilloclock.com hopes that no-one is offended by the deliberately light-hearted tone of this post, in referring to the decidedly serious topic of nuclear warfare.)

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  • Improper Prop!

    Veering slightly off the subject of the CRT and onto its cousin, the illustrious Magic Eye tube – it’s been a couple years since I wrote about the fortuitous visit to Robbie’s Place, where I picked up a beautiful Westminster ZA 617.

    Not a CRT, but it’s lesser cousin – a soothing Y63 magic eye valve

    Recently I was watching an episode of the British-Irish crime drama Quirke. Imagine my surprise when I spotted a ZA 617 in one of the scenes!

    The fascinating thing was that this particular scene was set in a convent in the United States. But this radio was likely never sold in America! First and foremost, the radio doesn’t support 120V operation. Second, the dial markings, barely visible in the blurry close-up, reflect European radio station frequencies of of the time. Also, Long Wave was not particularly popular for public transmissions in the U.S. (as far as I know).

    While it’s a clear case of an improper prop, the BBC had exceedingly good taste to choose this beautiful radio for the show. Long live magic eyes!

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  • The VGA Cube!

    The VGA Cube!

    It’s been a long while since I wrote about the 3″ VGA Display assembly, which was used for an RWR indicator in a fighter cockpit simulator.

    The customer came back and requested four more. But could I stack the boards to make the units more compact? Of course!!

    This particular assembly is rather tall because the client requested an in-built mains supply board, sitting at the bottom. The normal configuration using an external power pack is half the height. (In which case it’s not quite a “cube”…)

    With green filter and replica RWR escutcheon fabricated by the customer. How real is that!!

    And if you aren’t into aircraft indicators, you could always have a bit of fun!

    Is a VGA Cube right for you?

    Maybe. Or maybe not! These units incorporate binary blanking – I.e. The beam is either on or off; no shades of grey. Hence any VGA image composed of thick line art like RWR will display well, but shaded or coloured displays such as an attitude / horizon indicator would not work so well.

    Below is a Windows XP login screen… Not exactly a flattering image!!

    VGA Board – better and better

    The latest VGA Board rev 1.1x is small and cute, and is compatible with the standard Oscilloclock Deflection and Power Boards.

    In keeping with tradition, the VGA Board employs entirely analogue techniques to generate the horizontal and vertical sweep, triggered by incoming sync pulses. A high-speed analogue comparator with adjustable levelling is used to convert analogue RGB into binary blanking. Naturally, inputs are ESD protected so you can’t easily blow the chips!

    New VGA Board revision (left) – meaner and leaner!

    Like what you see?

    VGA Cubes are like any other Oscilloclock product – each unit is hand-crafted to order and fully tested so that I can optimise for the selected CRT and provide a decent satisfaction guarantee. To date I’ve made five – and always happy to discuss a sixth! If you have a passion for raster rendering, let me know!

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  • Burn-in? Nope!

    Many folks have asked whether screen burn-in, or phosphor burn, is not a problem. They are concerned by what was a frequent occurrence in the CRT monitors and oscilloscopes of yesteryear: a permanent scar prominently visible on the screen…

    Phosphor burn – this old spectrum analyser looks ‘on’ even when it’s off!

    To understand why this occurs, first think of an iron burn. If you deliver too much heat for too long into the same spot, your nice new Oscilloclock brand T-shirt will feature a prominent (and permanent) mark as shown below.

    Iron burn – this shirt’s fibres have been literally scorched!

    (I could push for another analogy, and describe livestock branding – but I think you get the message.)

    In a CRT, a beam of fast-moving electrons bombards the phosphor coating on the screen to produce an image. If the beam is too intense, or it is allowed to trace the same route on the screen over a long period of time, the phosphor compound may degrade and lose its luminance. The end result is:

    • The screen won’t light up well in those spots any longer.
    • The damaged areas may appear dark even with the power off – a ‘ghost image’.

    Interestingly, this damage does not actually shorten the working life of the CRT! (It does not affect the longevity of the heater, or the amount of gas permeating the vacuum.) However, it is certainly not attractive, and is most definitely NOT an effect you wish to observe on your fancy custom-crafted Oscilloclock…

    Keeping the ghosts at bay

    Happily, screen burn-in is not much a problem with the Oscilloclock. Let’s see why.

    1. CRT selection

    Some CRT types and brands are more susceptible to screen burn-in than others. There are a number of factors for this, and all of these are considered during CRT selection to minimize the risk of burn-in:

    First, there is the phosphor compound used. Some phosphors, just by their chemical makeup, degrade faster than others. More significant, though, is the fact that some phosphors require more energy (electron beam intensity) to produce the same level of visible light output as others.

    For example, a long-persistence blue P7 phosphor, such as used in the Model 1-S and the Prototype, is by its nature ‘darker’; it requires a higher beam intensity than the crisp green P1 or P31 phosphors used in many other models. The higher beam does make the P7 more vulnerable to burn-in.

    Different phosphors need different intensities to appear ‘bright’ – so some will burn faster

    Fortunately, the simple protection mechanisms in place in the Oscilloclock (we’ll get to these later) will avoid burn-in even on sensitive phosphors. The customer need not be concerned about this risk factor, and can select any of the available phosphors.

    The second factor is the thickness of the phosphor coating. The thicker the phosphor, the less burn-in for the same beam intensity. Some CRTs are infamous for having ridiculously thin phosphor coatings, making them extremely susceptible to burn-in. Sadly, some CRTs that are most readily available today fall into this category, and their data sheets even specify an incredibly short maximum longevity of 1000 hours. That’s less than 2 months of continuous use!

    Beware CRTs with short lifetime ratings – they may have ridiculously thin phosphors!

    Most CRT manufacturers did not publish lifetime ratings, nor did they publish specifications of phosphor thickness. In the Oscilloclock lab, I rely mainly on my and others’ experiences with the manufacturer, and pick and choose only the highest-quality CRTs. Expensive – but definitely worth it!

    The third factor is the use of any additional technology in the CRT that would allow for reduced beam intensities. The most common example is the aluminized screen, an additional coating on the rear of the phosphor. This coating reflects the light that would normally emanate from the phosphor towards the rear of the CRT, back into the phosphor (and the front of the screen). A much more efficient use of energy!

    However, this technology was a later development, so many CRTs with an aluminized screen tend to be rectangular and have an in-built graticule. These may not be as visually pleasing in a standard Oscilloclock as non-aluminized CRTs.

    2. Software (Firmware) protection mechanisms

    My favourite screensaver – Flying Toasters!
    (Image used under Fair Use terms)

    Remember the phrase “screen saver”? In the pre-LCD monitor days, most computers employed some form of software that would stop the same image being displayed for too long, to avoid screen burn-in.

    While there is nothing as fancy as flying toasters, the Oscilloclock has several mechanisms in place.

    1. Hourly XY Bump screen saver
      This feature simply shifts the image by a small amount in the X and Y directions every hour. The shift pattern repeats every 31 hours (a prime number), to ensure that every hour numeral will be placed in every screen position.
    2. Auto screen switch
      This feature simply cycles through the screens (clock faces) at regular intervals, configurable from 0 (off) to 90 seconds. This is by far the most commonly enabled feature, as it allows one to enjoy all the Oscilloclock screens without touching the control!
    3. Auto power off
      Strongly recommended by Oscilloclock labs, this feature simply turns the Oscilloclock off after a period of non-activity (not touching the control), configurable from 0 (off) to 90 minutes.

      This may sound counter-intuitive, but in practice, nearly all Oscilloclock owners are comfortable to turn their unit on just when they intend to enjoy it, and allow it to switch itself off. The exceptions are clocks that are permanent fixtures in offices and restaurants, in which case the owners manually turn their clocks on and off together with other appliances in the premises.

    These features are of course highlighted in the Operation Guide that accompanies every Oscilloclock.

    Summing it up

    So there we have it – there’s not so much to be concerned about after all. While CRTs do have a delicate phosphor coating, by selecting a decent CRT in the first place and looking after it in use, the risk of screen burn-in is drastically reduced. In fact, in 7 years of constructing Oscilloclocks, as of today not a single unit has come back for a CRT replacement!

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  • Metropolis Time

    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).

    The Metropolis 10-hour clock face!

    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.

    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.

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