Oscilloclock.com

Handcrafted Scope Clocks with circle graphics

Category: Circuit Theory

  • The Secrets to Long Life

    The Secrets to Long Life

    It’s a sobering thought, and not a particularly pleasant one, that your Oscilloclock might just outlive you…

    But let’s not dwell on such talk! The real focus today is the oft-asked question: “How long will my Oscilloclock last?”

    The honest answer is: we don’t know.

    However, we do know how we try to maximize longevity, and we do have repair and return statistics from 15 years of delivering beautiful Oscilloclocks. We’ll go through all of this with you!

    Your Oscilloclock

    There are many different models and styles of Oscilloclocks (see the Gallery), with infinite variations in terms of parts that make up the final product.

    But in terms of longevity, we can broadly categorize components like this:

    • CRT – the cathode-ray tube display
    • Hardware – the case, mounting supports, thermal parts, nuts and bolts
    • Oscilloclock boards – the electronics designed and built right here in the Oscilloclock lab
    • Original device circuitry – the host device’s original electronics that are kept in use (if any)
    • Harnesses and cabling – wires, plugs and sockets; both internal and external

    In today’s post, we’ll tackle the proverbial elephant in the room – the CRT!

    Your CRT

    Your clock’s cathode-ray tube is actually a type of vacuum tube. There is a glass enclosure, with a screen coated with chemical phosphor. It has a heater (or filament), and other electrodes made of special materials. These are welded to wires that are soldered to pins protruding through airtight seals in the glass.

    Each italicized word adds up to this: A CRT is quite fragile!

    The CRT – easily the most delicate part of any Oscilloclock!

    CRTs have many “failure modes” – and we’ve seen them all! Let’s explore.

    Failure mode A: Natural causes

    Vacuum tubes (or valves) rely on thermionic emission. Electrons are emitted from one of the electrodes called the cathode, when it is heated up and voltage is applied.

    In a CRT, thermionic emission is used to create the all-important electron beam

    In any vacuum tube, this emission capability decreases over long periods of active use. This is most commonly due to a degradation of the special emissive material and coatings that are used in the cathode.

    Your Oscilloclock’s beautiful CRT will face the same issue eventually. As the number of electrons bombarding the phosphor screen decreases, the image will gradually get dimmer and dimmer, until eventually it cannot be seen.

    How long will a new, unused CRT last before it succumbs? Well, manufacturers quote working lifespans of tens of thousands of hours of active use (heated and voltage applied). This equates to a few years.

    We want our Oscilloclock CRTs to last decades, not years! So what do we do?

    Secret 1: 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). Alternatively, owners can set a specific “Off at:” time.

    It may sound counter-intuitive, but in practice, all Oscilloclock owners to date have been comfortable to turn their unit on just when they intend to enjoy it, and allow it to switch itself off.

    For clocks that are permanent fixtures in offices and restaurants, staff manually turn their clocks on together with other appliances in the premises, and set them to turn off at the business closing time.

    Secret 2: CRT type and manufacturer selection

    While working with the owner to choose their CRT, we emphatically avoid tubes where the manufacturer quotes short lifetime ratings.

    Sadly, some CRTs that are most readily available today fall into this category. See the data sheet below, specifying an incredibly short maximum longevity of just thousands of hours!

    Q. What can be done for a CRT ‘on its last legs’?

    Sadly, it isn’t feasible to restore a dead CRT to factory condition. But there are two things that can be done before it reaches that state, to prolong the inevitable:

    Firstly, Oscilloclock owners can adjust the Intensity control, as described in the Operation Guide. This will drive the CRT harder and brighten the image.

    Secondly, here in the Oscilloclock lab, we can attempt a CRT rejuvenation. This procedure involves carefully applying higher-than-normal voltages to the heater, and between certain electrodes. Done correctly, this can ‘peel back’ a thin layer of the cathode surface that has degraded or suffered from ‘cathode poisoning’, to reveal a more emissive layer of material beneath.

    Q. Will a new (unused) CRT last longer than a used one?

    Theoretically, yes.

    BUT in all our experience at Oscilloclock.com, we see no evidence that new-old-stock CRTs last any longer than used ones.

    Why is that? Well, most CRTs we use are harvested from laboratory test equipment. Most operators typically switch lab equipment on only when needed – so the accumulated operating time is often very short.

    In fact, we openly encourage the owners to choose a pre-loved tube! We vet all our CRTs, testing them electrically and inspecting for any damage to heater, phosphor, glassware, or seals. No electrode is unturned; no emission-impacting detail is omitted!

    Failure mode B: Humpty Dumpty

    Humpty Dumpty sat on a wall…
    Humpty Dumpty had a great fall…

    Visit A Humpty Dumpty CRT for a truly woeful tale…

    If the CRT glass is cracked or broken, there will be rapid loss of vacuum inside, halting all electron emission. If voltage is applied, the heater will quickly burn out, due to oxidation.

    All the king’s horses and all the king’s men,
    Couldn’t put Humpty together again.

    Sadly, several CRTs have arrived at our lab in this woeful state.

    Secret 3: Shipping precautions

    We take great pains to ensure that Oscilloclock owners do not experience a Humpty Dumpty episode.

    • CRT mounting – in all Oscilloclock models we ensure the CRT is mounted with sufficient cushioning (silicon or rubber) against its mechanical supports.
    • Double-boxing – all separable components of an Oscilloclock are individually boxed prior to packing into a larger box for shipping.
    • Packing material – we use a combination of bubble wrap, foam peas, and Styrofoam to cushion the internal boxes and their contents.
    • Box selection – we love to recycle, and we have loads of used boxes on hand. We pick the stronger ones and make sure they are the right size – large enough to fit cushioning material, but never so large that the inner boxes might slide around!
    • Carrier – we have had extremely good results with the standard EMS service available from Japan Post, and this is what we always recommend.
    • Insurance – we always insure the shipment to a sufficient value.

    Thanks to this secret, to date we have only had one case of breakage for an item shipped out from our lab! And even then, the insurance claims process working with Japan Post was quite straightforward – if not even pleasant.

    Failure mode C: Gassy CRT

    No, CRTs can’t eat too many potatoes! But CRTs definitely do not like air.

    A CRT may become “gassy” if too much air leaks in via the pin seals or a fracture in the glass, such that its internal self-healing mechanism (formed by the getter electrode) is overwhelmed.

    This CRT is gassy, as indicated by white precipitate near the “getter”

    On a gassy CRT, the image will become dimmer and dimmer until it disappears entirely.

    While there is no true remedy for this malaise, an owner can postpone the inevitable by adjusting the Intensity control. And in rare cases, the CRT rejuvenation procedure described earlier may stimulate the getter electrode to mop up some of the excess gas.

    Secret 4: Avoid potatoes mechanical shock

    Gassy CRTs crop up occasionally, usually as a result of excessive mechanical stress or shock.

    Besides shipping precautions (Secret 4), we are even careful when storing CRTs. Being situated in the Japanese archipelago, the Oscilloclock lab and all its contents must endure significant earthquakes occasionally.

    We therefore place the most precious CRTs in strongholds – small cavities in the woodwork that suffer less shaking and are very unlikely to collapse (even if the rest of the lab does). Touch wood!

    Our miniature lab securely houses more than 130 rare CRTs…
    … but where?

    Failure mode D: Phosphor burn

    Roughly 10% of the CRTs we harvest exhibit a permanent scar, prominently visible to the naked eye…

    Phosphor burn – it 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!

    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 result:

    • 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’.

    Devastatingly, it just isn’t possible to restore the phosphor. But since these CRTs are otherwise perfectly healthy, we put them to good use in the lab for testing and experiments.

    Secret 5: Choose a decent CRT

    Some CRT types and brands are more susceptible to screen burn-in than others. Some factors include:

    • The factory list price (you do get what you pay for)
    • The manufacturer’s credit rating for reliability
    • The phosphor compound used
    • The thickness of the phosphor coating
    • Any additional technology; e.g. aluminized screens

    For more details, see our deep-dive post: Burn-in? Nope!

    Secret 6: Screen-savers and other protection mechanisms

    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.

    In addition to Secret 1 (Auto power off), Oscilloclocks have several more screen-saving features that protect the phosphor:

    • Hourly XY Bump – shifts the image by a small amount in the X and Y directions every hour
    • Auto screen switch – cycles through the screens (clock faces) at regular intervals
    • Bright/dim control – switches between preset beam intensities via a front-panel control (on some models)
    • Intensity control – manually adjust beam intensity if required to suit darker rooms

    For more details, see our deep-dive post: Burn-in? Nope!

    Failure mode E: Disconnected electrode

    Very rarely, the weld between an electrode and its connecting wire fails. Or the soldered joint between the wire and the external pin fails.

    The symptoms depend on which electrode has been disconnected, but one thing is for sure: the CRT becomes defunct. How awfully sad.

    This cutie is perfectly healthy.. Except, it can’t focus. See the weld failure at right ..

    Secret 7: Cry and move on…

    I would like to simply write, “Choose a reliable manufacturer.” However, they don’t get much more reliable than Tektronix!

    Besides protecting the CRT from mechanical shock (see previous Secrets), all we can do is accept fate…

    Failure mode F: Open heater

    A CRT heater (filament), just visible

    Remember incandescent light bulbs of yore, with a delicate filament wire suspended inside the glass? They burned out over time – typically with a break in the wire that you could even see with the naked eye!

    Well, the heater in a CRT is also formed from filament wire (albeit with different metals designed to emit more heat than light). If a CRT heater burns out, the cathode cannot be heated sufficiently to emit electrons, and the tube is rendered useless. A sad, sad state of affairs…

    But what causes such failure?

    Well, when did light bulbs typically fail? Yes! Right when you switched them on!

    The reason is that a cold filament has a very low resistance. When you apply voltage, a huge amount of current flows (called inrush current). This settles as the heater warms, but the initial power and sudden temperature change causes metal fatigue. And after many switch-on cycles, the wire can break.

    Secret 8: Soft-start!

    The best way to preserve the heater is to limit the inrush current, so that the filament can warm up gradually. Every Oscilloclock employs one of the following 3 types of inrush current limiter:

    1. The sacrificial lamb – a light bulb!

    In this scheme, we simply place a specially-selected incandescent light bulb in series with the CRT heater. Upon switch-on, most of the supply voltage is applied to the light bulb’s filament (because the CRT heater’s resistance is low), making it light up brightly.

    Primitive. Low-cost. Yet immensely effective!

    As the CRT heater gradually warms up, its resistance increases. The voltage across the light bulb decreases, making it dim and cool down, and its resistance lowers. By this time, the CRT has fully warmed up and stabilized, with most of the voltage now shifted to the CRT heater.

    Functional, AND beautiful to watch! Besides the Exo in the video, we’ve used it in the Heathkit OR-1 Oscilloclock and a few other custom pieces.

    2. Mister thermistor

    These long-legged beauties are called thermistors. They have an odd characteristic called NTC (negative-temperature-coefficient). The hotter they get, the less their resistance!

    Does that sound familiar? Yes! They can replace the light bulb used in method (1) above. Most of our Oscilloclocks employ these devices, because they are reliable, predictable, and very small.

    Nonetheless, we enjoy the switch-on supernova of the old-fashioned light bulb. And some owners do, too!

    3. Electronic soft start

    Both light bulbs and thermistors are passive devices; their resistance vs. temperature profile is known (and can be charted in a specifications sheet). BUT they are not aware. They don’t have any kind of feedback loop, so they don’t actively control the voltage across the CRT.

    Recent Oscilloclock Power Board designs provide an active soft-start option. This is a circuit that dynamically ramps the output voltage up from 0V to the final voltage in a preconfigured number of seconds.

    Effective and reliable, but just a little more complex!

    Q. Will running the heater at a lower voltage prolong the CRT?

    No. According to many folks, running filaments at lower voltages than specified can accelerate “cathode poisoning” – degradation of the cathode material due to absorption or chemical reaction with trace foreign substances. We don’t recommend this.

    Q. “Sacrificial lamb” approach – won’t the light bulb itself die?

    Yes, eventually. However, it will certainly outlast the CRT filament. Although the light bulb filament does suffer a high inrush current, even a cold CRT presents a small resistance into the circuit. The voltage across the bulb at turn-on is therefore less than its rated voltage, and this extends its life.

    Q. Isn’t there something that can be done to restore a CRT heater?

    Maybe. Some folks have managed to ‘fuse’ a broken heater together, by injecting a very high voltage (thousands of volts) across the gap. The resulting arc effectively welds the broken filament. We haven’t yet had the pleasure of trying this, but if we do we will certainly write it up for you!

    Replacing the CRT

    Fact: In 15 years of crafting Oscilloclocks, not a single unit has ever come back for CRT replacement!

    That said, every CRT we shipped will reach its end of life. It’s just a matter of time.

    But don’t despair! Oscilloclock carries spares for most common tubes, and we can supply and replace them. Some owners even choose to purchase spare CRTs with their original order, so that they have them on hand.

    Q. What about rare CRTs?

    If a clock was crafted from a particularly rare CRT, there may be no spare available. But again – do not despair! We can work with the owner to select another type of CRT, and modify their precious device to suit. By rejuvenating their clock ‘with a twist’, the owner may experience even more of a thrill than if we simply restored it to its previous state!

    A rare CRT: type D4P. Don’t worry – we can replace it with something!

    Q. Can owners replace the CRT by themselves?

    We always recommend shipping clocks back to the lab for CRT replacement.

    However some models, especially those in the Oscilloclock Exo series, employ a simple and safe mechanism to swap CRTs – and we provide instructions in the Operation Guide for doing this.

    Q. Does Oscilloclock.com produce or repair CRTs?

    No. We dream of one day establishing a CRT factory. Or at least a CRT repair facility. However with all the toxic chemicals, high vacuum, glasswork, and intricate welding involved, this is likely to remain a dream.

    Q. Are new CRTs being manufactured anywhere in the world?

    Yes – some types of CRTs are being manufactured in some countries. However many are not suitable for Oscilloclocks. They may employ electromagnetic deflection (which we don’t yet support), they are special-purpose for military or aerospace applications (too expensive!), they are very cheaply-produced (not reliable), or they have short lifetimes per design and require frequent replacement.

    Swappable CRTs!

    Many of our ‘Full Package’ type clocks (see Gallery) support display swapping.

    Essentially, we craft complete additional display units, which the owner can swap in at will simply by swapping cables to the Control Unit. There is no need to open a case, touch the CRT itself, or any form of delicate operation.

    This is normally used to change the ‘mood’ of an Oscilloclock, by swapping in different phosphor colors. But it also can be used to more easily swap in a replacement CRT.

    Do you want long life, both for yourself and for your precious electronic devices? Are you tired of modern society’s throwaway culture, built-in obsolescence, and device non-serviceability? Our goal: electronic artwork that might be passed down a generation (or more) in actual working order!

    Stay tuned for Secrets Parte II, where we will explore the life of other components!

    , , , ,
  • Z Core makes Blanking easy!

    Z Core makes Blanking easy!

    Here at the Oscilloclock lab there’s nothing more pleasurable than helping put a cherished vintage oscilloscope back into action. A new lease on life!

    That’s why when [Chris] reached out about his early 1970’s Conar 255 oscilloscope, wanting to convert it into a Vectrex gaming machine, we were naturally excited!

    The Conar 255 – “space age technology” per NRI Journal Nov/Dec 1973
    Beautiful vector graphics! Image by When Chemists Attack

    The original Vectrex was an incredibly cool device. Instead of the pixelated, blocky graphics of the time (anyone remember Pac-Man?), the system used vector graphics to draw smooth line-art images. Each vector was a straight line, or a smooth arc, connecting point A to B. Vectrex games were true works of art, and the original hardware is quite rare (and $$$)!

    Scopetrex

    The Scopetrex

    Well, [Chris] caught the vector graphics bug. But he decided to build a Scopetrex – a hardware emulator that allows you to run Vectrex games on an oscilloscope! He would theoretically just connect this to the Conar 255’s existing X, Y, and Z (blanking) inputs.

    We like this “minimum invasion, maximum re-use” approach. We’ve gone down this route numerous times to craft Oscilloclocks out of still-usable hardware. (The alternative? Install a full set of modern boards that drive the CRT directly.)

    Sample specimens of “minimum invasion, maximum re-use”

    [Chris] got down to planning. He could interface the X and Y inputs easily. But he faced a problem with the Z (blanking, or intensity modulation) signal, which instructs the scope when to turn the beam on and off:

    • The Scopetrex outputs a 5V DC digital blanking pulse.
    • The Conar requires at least 20V peak-to-peak blanking signal – and employs analog AC coupling.

    We’ve solved this mismatch problem before using various non-standard Oscilloclock board setups and complex hook-ins to the existing circuits. Always on a case-by-case basis, always unique.

    But now, at last, it was time to standardise the process. To make it easy. To adapt any vintage oscilloscope for digital blanking from a microcontroller! We proudly announce the next member of the Core family: The Z Core!

    The Z Core (in this case, a Z Core 2 Ex) …

    … joins the Oscilloclock Core family!

    How to install it

    Believe it or not, the minimal installation requires just 3 steps. For almost any oscilloscope! The Z Core effectively sits in series between your device’s blanking supply and the CRT grid.

    1. Snip the wire connecting to CRT grid.
    2. Connect the orange wire from the Z Core to the circuit side of the cut wire.
    3. Connect the green/yellow wire to the CRT grid.
    Snip.
    Connect!

    Visit the Z Core Support Page for lots more detail, including the obligatory warnings about high voltage. There are also details on how to connect the Z Core to your controller, detailed specifications, and some fun Q&A to help answer your most burning questions!

    The Z Core 2 Ex!

    We’ve wanted to develop a dedicated, built-for-purpose Z Core product for a very long time. This would consist of a single, miniaturised, low-power board called (ingeniously) a “Z Core Board”, and a few harnesses.

    But [Chris] didn’t want to wait for Oscilloclock labs to work through its ever-growing bucket list. Could we deliver within 2024?

    Yes!

    In past retrofits such as the Kikusui 537, we’ve taken spare boards that were originally designed for fully-featured Oscilloclocks, and partially populated them with only the necessary components to serve the blanking purpose.

    Partially populated Oscilloclock Power Board

    For [Chris], we found an almost fully-populated new-old-stock Power Board v2.27 and compatible CRT Board v1.21 lying around, just dying to be used and loved by someone. Older revision boards do tend to be set aside, as folks want the latest and greatest.

    With just a few minor modifications, this assembly shipped – and is now branded as the Z Core 2 Ex. The “2” refers to the Power Board’s major revision, and the “Ex” stands for “external blanking amplifier” (the function of the CRT Board). The Power Board rev2.2x series boasts an on-board blanking amplifier, but this section wasn’t already populated. What a great opportunity to use up a stock CRT Board!

    [Chris] will be happy. And we’ll keep up this spirit of minimising waste. You’ll see some other Z Core assemblies popping up in future: a Z Core 1 Ex, a Z Core 2, and potential variations of Z Core 3’s.

    And finally, one day, a genuine dedicated Z Core will be born!

    Why your scope needs a Z Core …

    Many old oscilloscopes simply don’t have any input for Z blanking, Z axis, intensity modulation, or cathode modulation. (Look carefully – it goes by many names!) Or, the input may be there, but it’s not compatible with a microcontroller. Why couldn’t the designers offer a decent interface?

    Well, it all has to do with high voltage! To get there, let’s cover how CRTs work in just three short sections:

    Gun

    A cathode-ray tube (CRT) has an electron gun that shoots electrons at the phosphor molecules on the screen. The electron beam is deflected by putting positive and negative voltages into electrodes placed in the CRT’s neck, and this is how patterns are drawn on the screen.

    This is how a CRT works. It’s awesome.

    But the electron beam has to be turned on and off, to break the pattern and make meaningful images on screen. This is known as blanking.

    Blanking

    Oscilloscopes, particularly, have to blank the beam when it goes back (retrace), from the right to the left again. If there were no blanking, you’d see a retrace line – wickedly cool for us artists, but devastatingly distracting for engineers who want to focus on the waveform itself!

    Retrace lines – arty but not desirable

    Oscilloclocks also rely on blanking. In Circle Graphics, where all figures are composed of lines and circles, blanking is crucial to creating meaningful segments. For example, a “C” is readily created from an ellipse “O”, simply by blanking the beam at just the right place!

    A blanking pulse kills the beam to get a ‘C’

    Grid

    CRTs are designed for blanking. There’s a valve-like electrode called a grid that sits inside the gun, just in front of the cathode where the electrons are spat out. If you inject a negative voltage into the grid (compared to the cathode), it repels those electron babies and sends them back where they came from. They don’t bombard the screen, and no more light is emitted. Blanking in action!

    Titillating! Electron field density is reduced when a negative voltage is applied to the grid!
    A fuller explanation – from The Bible
    The bible

    A change in grid voltage influences the field distribution of the first lens, and in so doing controls the emission from the cathode. For any fixed value of voltage applied to anode 1, it influences the number of electrons which pass through the cross-over point. Let us see how this comes about. In Fig. 5-17 is shown the field distribution in the first lens for two values of grid bias, O and -30 volts, and a fixed value of voltage on the plate.? It is clearly evident that with zero bias, the area adjacent to the cathode, between the cathode and the control-grid aperture, has a comparatively high positive potential as the consequence of the field between the control grid and the first anode. Under such conditions of zero grid voltage, it has been found that the area of the cathode which is emitting corresponds approximately to a projection of the area of the grid aperture; the maximum number of electrons are passing through the grid opening and the beam-current density is high.

    When the control grid is made negative by an increase in the bias, —30 volts in the illustration, the field distribution in the vicinity of the cathode is altered so that only the center of the emitting surface is behaving as an emitter. The other areas are influenced by the space charge and effectively are not emitting. The result is a reduction in beam density and several other related effects.

    High voltage

    So – back to the high voltage aspect. The cathode and grid are usually about 2kV (that’s right – 2,000 volts!) negative compared to the rest of the circuits. If you connected an external input signal directly to the grid, something would fry.

    Old-school oscilloscope designers took a very easy (read: cheap) solution: they stuck a high voltage capacitor between the grid (or cathode) and the external signal. This is called AC coupling because the capacitor blocks the DC voltage (2kV), and only couples through the AC (the fluctuating blanking) component of the signal.

    AC coupled external intensity modulation in the Conar 255 (L) and the Trio CS-1554 (R)

    This method of intensity modulation was fine for the regular, repeating signals observed in old TVs and radios. But it isn’t what [Chris], or so many millions out there like him, needs! They need to send through an irregular, sometimes not-fluctuating-at-all (i.e., DC) signal. They need DC coupling! And it has to be isolated – standing off more than 2kV!

    And there’s another voltage related problem: the grid has to go substantially negative with respect to the cathode, in order to completely block the electron flow. We’re talking 20-50V typically. This is not a voltage that a modern microcontroller board will deliver! This requires an amplifier.

    Summing it up

    So that’s it! Just three(?) words. We need an isolated DC-coupled amplifier. And it needs 2kV isolation with a 10x amplification factor.

    Welcome to the Z Core!

    Demo

    No assembly can leave our lab without being fully tested, and without a demonstration to ensure the customer’s utmost satisfaction. Here’s how the demo went:

    The host device: Trio CS-1554

    This venerable Trio (also branded as Kenwood) hails from around the same era as the Conar 255. It was attractive, had fairly good specifications, and a low(-ish) price tag, making it very popular both in Japan and overseas. Documentation is freely available and… more importantly, I had one lying around!

    Look carefully – it’s bulging and leaking!

    Of course this device is full of high voltage oil capacitors. These were effective in their day, but they break down over time, and things get very nasty. One particular HV capacitor in this unit was overheating to the point that the metal case had warped, and oil was even leaking out! Ick.

    A few modern-day capacitors hacked together replaced the leaky unit and saved the day. Onwards!

    The controller: Oscilloclock Connect

    Oscilloclock Connect

    As mentioned on the Availability page, one lovely Oscilloclock Connect unit is in stock. What better controller to verify the Z Core’s performance?

    The demo

    1. Connect Connect X output to Trio EXT HORIZ input at rear 1
    2. Connect Connect Y output to Trio CH1 vertical input
    3. Connect Connect Z output to Z Core input 2
    4. Connect Z Core outputs to Trio CRT grid and grid circuit (as shown in earlier section)
    1. Incompatibility! The Trio’s horizontal input seemed to want 10V peak-to-peak for maximum deflection (this is way off its original specs of 250mV/cm. I think it’s broken!) The Connect by default has only a 3V peak-to-peak output signal. The image is going to be small… ↩︎
    2. Trickery! The Connect by default is designed for a display device with a high-impedance Z input. The Z Core 2 Ex has a low-impedance input and 15mA drain at 5V. A temporary mod was needed in the Connect – which was promptly reversed after the test. ↩︎

    The result? A relatively clean image, albeit small! But the blanking works well. [Chris] was okay with the jagged edges and other blemishes; these are attributable to the Trio’s rough condition.

    Performance testing

    The Oscilloclock cave is not a precision testing laboratory. But we do have a significant collection of equipment, and every piece plays its part. In this case, we deployed a Hewlett Packard 1901A Pulse Generator.

    Choosing amongst a plethora of delightful old oscilloscopes, we stayed with the HP theme and used a venerable but still digital HP54615B.

    Yes! This HP has an undocumented Tetris game built in!

    The setup was simple:

    1. Set up the pulse generator for 100kHz square wave
    2. Set rise and fall times to minimum (around 10ns)
    3. Set output to 5V and connect to the Z Core’s input
    4. Connect a 20pF capacitor across the Z Core’s output, via the standard 200mm 22AWG harness
    5. Connect Ch1 of the scope to the input, Ch2 of the scope to the output

    Results

    MeasurementAssembly: Z Core 2 Ex
    Waveform base voltage-46V
    Rise time130 ±10 ns
    Fall time180 ±10 ns
    Propagation delay120 ±10 ns
    Effective bandwidthDC to 3 MHz
    (limited by rise/fall time)

    These results were satisfactory. But at some point, we’ll try the same with a Z Core 1 and a Z Core 3. And one day – a purpose-built pure Z Core. Stay tuned!

    In conclusion

    Well, that’s a wrap! The tested assembly has now shipped, and soon [Chris] will be able to try out a Scopetrex on his minimally-modified Conar oscilloscope. Fingers crossed!

    For more technical info, fun facts and Q&A, check out the Z Core Support page. And for a peek at our range of gadgets, be sure to check out the Gallery.

    , , ,
  • Garmin “puck” USB adapter – Finale

    Garmin “puck” USB adapter – Finale

    In the first post in the series, 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.

    In Part 2, we went through the design of an Oscilloclock Garmin 18x USB Adapter, that would allow the GPS to connect to a PC where the Garmin software runs to upgrade the firmware.

    Now we conclude the series, with a treatise on the construction of the Adapter. Enjoy!

    The final design

    Here’s the design we arrived at in the last post. Let’s go through the steps to build it!

    Fish out Fake Chips

    TTL serial to USB adapter – watch out for fakes!

    The key component required is a decent TTL serial to USB adapter with programmable inversion on the signal lines. But here we have to careful: many low-cost adapters out there are built around fake FTDI chips!

    As mentioned before, we at Oscilloclock are pacifists. But if we were to wage war against anything, it would be fake components. They are unsafe, unreliable, unworkable, and entirely unethical. You get what you pay for, if you pay the right people. The people who design, manufacture, and support the real McCoy.

    Besides ethics and reliability, there is also a practical reason we must avoid adapters based on fake FTDI chips – often the fake chips are not programmable. A true no-no. So watch out.

    Program the inversion

    FTDI provide a nifty utility called FT_Prog. Below shows the utility running on a PC with the adapter connected, and configuring to invert the transmit (TXD) and receive (RXD) signals.

    Is it complicated? No – quite the inverse!

    Dividing the input signal

    We need to figure out the most elegant way to install the voltage divider – the two resistors we described earlier that reduce the impact of noise.

    The cleanest way seemed to be to install the 1.2k shunt resistor directly across the receive and ground pins in the adapter itself, as below.

    What about the 270 ohm series resistor on the RXD line? Well, installing this inside the adapter unit itself would require cutting tracks on the PCB. And that would compromise our effort, reliability, and aesthetics goals! So instead, we’ll insert this into the cable later on.

    Cable Connector Conundrum

    Recall that [Andrew] has two Garmin 18x units – one fitted with a small GPS connector and the other with a large connector. Wiring up two independent cables would have been natural. However, the TTL Serial to USB adapter came with only one cable pre-fitted with the necessary “DuPont” (a.k.a. Qi or 2550) connector.

    DuPont, Qi, 2550 – they look low-cost but… Read this excellent writeup and weep

    What’s the big deal? Surely we can just attach a Qi connector to another cable?

    Ha! Connector tech is never that easy! It turns out that to make a perfect connection with Qi connectors, you need a special crimping tool. The Oscilloclock Lab does not have this tool. And we do NOT compromise on perfection! Given that this adapter is not the best reason to invest in an incredibly expensive tool, we decided to use the single pre-fitted cable and split out to two GPS connectors, with the larger one serving as the split point.

    (In hindsight, we could have separately purchased another quality cable that was pre-fitted with the connector. Next time, folks!)

    Wire up the cable

    Our beloved ultra-quality Hirose connectors are a joy to look at, and a joy to use. But wiring the tiny smaller units up with high precision doesn’t exactly “spark joy”. Still, we persevere…

    Now we need to install the 270 ohm series resistor. We simply cut the wire and splice it in.

    A bit more heatshrink applied, and we’re done!

    Closure at last

    Using the 18x USB adapter, [Andrew] is at last able to upgrade his pucks and enjoy his clocks in their full glory with GPS-synchronized time and date once again!

    Instructions for how to upgrade the software are posted on the Support – Garmin 18x page.

    Did you enjoy this series? Stay tuned for more, as Oscillolife returns to nor….. Okay, not quite normal, but at least it returns!

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  • Garmin “puck” USB adapter – Part 2

    Garmin “puck” USB adapter – Part 2

    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 USB
    18x PC
    18x 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:

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  • Longevity, and the Garmin “puck”

    Longevity, and the Garmin “puck”

    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.

    Toshiba ST-1248D Oscilloclock - GPS connector
    -- We don't scrimp - we only crimp!
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