In the previous post, we looked at the Garmin 18x LVC “puck”. We talked about a particularly insidious issue that affected [Andrew] – both of his GPS units. And we saw that Oscilloclock owners really need to be able to update the firmware in these units.
We introduced the Oscilloclock Garmin 18x USB Adapter, that allows an Oscilloclock owner to connect their puck to a PC to enable the firmware upgrade.
In this post, we’ll take a look at the design of the Oscilloclock Garmin 18x USB Adapter. It wasn’t GPS satellite launcher (a.k.a. ‘rocket’) science, but it certainly wasn’t as straightforward as it might seem!
The Garmin 18x LVC electrical interface
Referencing the manual, the Garmin 18x series comes in 3 basic interface variations:
USB – USB 1.x interface, with a USB(-A) connector to plug into a PC
PC – RS-232 serial interface*, with a DB9 connector to plug into a PC, and a massive cigarette lighter adapter plug to obtain power
LVC – RS-232 serial interface*, with no connector – for wiring into a device
18x USB18x PC18x LVC
For our Oscilloclocks, we use the LVC variation and fit an attractive custom connector solution, avoiding the PC variation with its venerable, utilitarian, and aesthetically unpleasant DB-9 connector and cigarette lighter plug combo. (We may buck the trend one day and intentionally fit such sockets into that special retro clock build – who knows?!)
* Astute readers noticed the earlier asterisks. PC and LVC units are not quite true RS-232; their output voltage swings between 0V and +5V. Not so with devices having true RS-232 interfaces! A swing from -25V to +25V is legal and also lethal for any unsuspecting microcontroller. In the Oscilloclock design, we take advantage of Garmin’s voltage range cap to avoid having additional circuitry to adjust voltage levels.
Interfacing the 18x LVC to a PC
To upgrade the GPS firmware, the 18x LVC needs to connect nicely to a PC. But [Andrew] is an Oscilloclock Owner. He deserves more than just a good electrical connection. The interface also must be elegant and aesthetically pleasing, lightweight (for shipping), and easy to build. And – most of all – it has to be interesting enough to write a blog series about!
We can start with Figure 1 in the manual, which describes the most basic interface hook-up possible.
This interconnection option assumes two things: the PC has a DB-9 serial port, and there is a power source.
If we extend this option slightly, to take power from the PC’s USB port, we arrive at this:
A few months ago, [Andrew] – of Metropolis Clock fame – reached out for help. He had just pulled his lovely Oscilloclocks out of storage to put on display, when he observed odd behaviour in both units: the time was accurate, but the date was stuck – to some random date back in 2003!
What on earth was going on?
What’s going on was not “on Earth” after all! [Andrew]’s clocks synchronise time and date against satellites, using an external Garmin GPS unit. And this unit happened to have a serious flaw. In this series of three articles, we’ll look closer at this accessory, identify this issue, and see how we were able to resolve it. Enjoy!
Our longevity dream
We want your Oscilloclock up and running as long as you are – and even beyond! Our dream is to see these beloved devices inherited by loved ones, and even available on the second-hand market as antiques one day.
In an era of throw-away technology, we flaunt an unthinkable target: Decades of trouble-free* operation.
* Excluding the CRT itself – although we really try hard with that as well, as this post explains!
To maximise usable lifetime (and safety!), we construct Oscilloclock units from the finest materials and components available. As part of this, we also select manufacturers that guarantee their components and provide decent after-sales support.
And Garmin is one such manufacturer…
Welcome to the Garmin GPS ‘Puck’
All Oscilloclock models that synchronise time using an external GPS unit have so far been supplied with a Garmin 18x LVC GPS unit, colloquially known as a ‘puck‘. (Note: to extend the lifetime of the pucks, we do not recommend using them on the hockey court.)
Now, this is not the smallest external GPS unit on the market today. But it has been available from Garmin since 2007, and is even being manufactured today! It is one of the most sensitive, robust, and well-supported units out there.
(Of course, for every new Oscilloclock delivered we evaluate afresh based on the latest devices available.)
This puck has a special connector …
How many times have you relegated an expensive laptop, phone, or other random device to the trash just because the power socket or headphone jack failed? Some of the weakest components of any electrical device are its connectors – plugs and sockets.
To combat such failures, your puck is wired with an exceptionally high quality connector from Hirose. This connectivity solution is not only robust, it even feels good! There’s a lovely audible and tactile ‘click’ when you engage the plug, and it locks securely in place. And unlike cheap chrome-plated connectors, we’ve proven that these babies do NOT corrode, even after a decade.
Recently I had an enquiry from [Frank], who had just begun a life-long love affair with scope clocks by purchasing one on eBay. The clock was great – but he felt that the two available screens (simple analogue and digital clock faces) lacked a certain oomph.
He then stumbled across Oscilloclock.com, and in his smitten state immediately reached out with his number one question: just what screens are available on an Oscilloclock?
Well, let me save Frank’s time trawling through years of blog posts. Right here in one place are most of the Oscilloclock screens and features created to date.
Enjoy the show!
Standard Time Screens
These stock-standard analogue and digital time screens may be quite simple, but they do evoke the ‘retro’ look that most people appreciate.
And you can flip a menu setting to display days, months, years in Japanese:
There are also some ‘random’ screens that add in a bit of dynamic visual entertainment:
Random number screen
Random letter sequence screen
Random four letter word screen (clean words only, by default!)
Random phrase screen (the phrase list is typically customized to a theme)
Over the years many folks have requested that I render custom logos in Circle Graphics. Here are some examples:
“Seasonal Treats”
Up next are some fun, mildly interactive animation features. Not exactly screens per se, these animations pop up after a predefined period of inactivity – but only during certain months of the year. Can you guess which months?
There are far too many configuration menu and test screens to present here. Fiddle to your heart’s content!
Q. How are screens switched?
Screens are switched simply by rotating the control knob in one direction or other.
There is also a configurable auto-switch feature; the screen is changed every 90 seconds in a predefined order (with the exception of some animation screens). The display time is configurable, and the auto-switch feature can also be turned off for those who prefer to switch screens manually.
Q. How are screens selected & configured?
Customers can request screens to include and/or specify the switching order. The configuration is done here in the lab before clocks are delivered.
Oscilloclock also provides a firmware upgrade kit, which allows the customer to upload a revised version of the firmware into the clock themselves. Using this, updates to screens and other features can be uploaded without shipping the clock back to the lab.
Q. What is the process for rendering a custom screen or logo?
We typically prepare a mock-up based on the customer’s description, sketch, or image file. This is tweaked as needed until the screen looks just right to the customer.
As I’ve hinted before, your friendly Oscilloclock gang is entirely pacifistic. We abhor the thought of actual military activity in this modern day and age. BUT we love games just as much as anyone – and we also love light-hearted movies with happy endings!
So when [Ian] (of Bunker Club Clock fame) came up with the idea of a feature based on the iconic 1984 flick “War Games“, I pounced on the chance!
Now, this may look like a simple animation. But Ian’s Oscilloclock is powered by a tiny processor with minimal specifications, and 100% of the code is written in assembly language. Implementing this baby in assembly and keeping within just 3K of RAM was quite an accomplishment!!
About the host clock
The gorgeous model shown here is a painstakingly-retrofitted Heathkit CO-1015 Engine Analyzer. It’s the perfect play-toy for any serious motor-head who grew up during the Cold War!
First up on the custom build list is the original meter fitted with amber LED lighting and ticking audibly each second. (And yes, the tick intensity can be easily adjusted.)
Next up, there is the optional External X-Y input feature. Normally, this is used for plain and simple Lissajous figures like the below…
… but by tweaking some settings, we can get some segments of Jerobeam Fenderson’s incredible Oscilloscope Music Kickstarter video to display quite nicely!
Peeking inside the Engine Analyzer Oscilloclock is also a must-do! Not only is this visually appealing, but you also get a significant olfactory kick from the sweet smell of vintage electronic components…
Attractive Oscilloclock boards and cabling, neatly tucked awayThe original circuit is completely bypassed – but still looks awesome!
Tech Talk – Strategies, Maps, and Missiles
The War Games feature uses the Oscilloclock’s Sprite Engine module to display the world map and up to 9 missiles when the W.O.P.R. system is simulating various war strategies.
32 of the 130+ strategies seen in the movie are implemented. For each strategy, a random number of missiles are launched along a predefined Primary trajectory, followed by a random number of missiles along a predefined Retaliatory trajectory. If any of the 9 missiles remain, they are launched along randomly selected (but predefined) trajectories.
Trajectories are predefined because computing them using 8-bit arithmetic would consume a huge number of cycles! At least, a small amount of randomness is added to the launch position and velocity parameters at run-time, to make things more interesting.
As the simulation progresses through the strategies, the speed of the launches increases and the delay between launches decreases. This gives a similar effect to that in the move, where WOPR moves through strategies at warp speed until it realises that there is no winning this game…
A Joint Effort
Creating a huge number of realistic trajectories (68 in total), translating start and end X and Y coordinates from latitude and longitude into the Oscilloclock’s Cartesian plane was a task of mind-blowing proportions! Here we see our 2nd junior technician eagerly earning his room and board.
Like what you see?
Are you a petrol-head? You need an Engine Analyzer ticking over at your bedside or in your office! Were you brought up during the Cold War, perhaps in the Soviet Union or in the US? Get the War Games feature and fry the world safely! Contact me if you like what you see.
(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.)
Many folks have asked whether screenburn-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.
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.
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!
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!
