Category: CRTs

  • 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.

    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!

    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.

    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!

  • Exo 3KP1

    Huh? R2D2’s cousin? C3PO’s sister?

    No! We’re not here to talk about a new Star Wars character! The 3KP1 is a type of cathode-ray tube that was used in many low-cost 1960s-1970s Japanese oscilloscopes.

    And the Exo is a series in our Oscilloclock range that fully exposes the CRT both visually and physically, much to the delight of the owner and visitors – while of course protecting high voltage areas from dust and prying fingers.

    The Exo 3KP1!

    First crafted for [Jerry] back in 2019, the Oscilloclock Exo 3KP1 is the default character in the Exo series, alongside the arguably oddball Oscilloblock – Summer Dusk Edition and the slightly more exotic OscilloTerm Exo B7S4.

    There’s nothing more soothing than the green glow of flourescent phosphor backed by the amber ambience of the CRT heater. Ahhh, that’s nice.

    This Exo shipped with all the “standard” screens, like the analog clock face below. But why stop there? We’ve done custom logos, movie themed features, oddball time systems, and so much more!

    From the top, [Jerry] and his dinner guests can readily inspect every square centimeter of the CRT and its exquisite innards. Cooool.

    Inside the unit, neatly tied cabling lends an air of gentle sophistication, while the green of the circuit boards harmonizes well with the phosphor.

    Even as a baseline model in the series, the Exo 3KP1 is distinctly attractive.

    [Jerry] did make some choices along the way, including which CRT to use. Let’s explore his CRT options in more detail!

    Round vs. flat

    As shown in the photos, the CRT that [Jerry] selected has a slightly convex face. This was the standard shape of the original 3KP1 type CRT, and is a perfect choice for the Exo case style, as it visually softens the glass edge exposed in front of the acrylic ring supports.

    The round-faced 3KP1 was superseded after some years on the market, by a flat-faced version: the 3KP1(F). This version is rather more commonly found and they are delightful to use. We used a 3KP1(F) in the Exo series Oscilloblock, as shown at right.

    Which would YOU prefer – round or flat?

    Phosphors and flavours

    [Jerry] had another choice to make: the phosphor! While the standard phosphor of most CRTs of the day was green, other colours were available such as amber, blue, white, purple. Such CRTs are more rare, but we have some… and so could Jerry!

    The “trailing effect” on a long-persistence CRT

    There were also varieties of CRT with different persistences; i.e., how long the trace would continue to show on the screen! We love this shot of the moving second hand on a blue, long-persistence CRT:

    And, we just happened to have a 3KP7 CRT in stock with exactly these characteristics.

    But in the end, [Jerry] wanted the nostalgic look of an old green-screen computer monitor, and chose the stock-standard 3KP1.

    Nice choice!!

    The longevity question

    [Jerry]’s clock shipped with a used 3KP1 CRT. Pre-owned, pre-loved, and pre-21st century.

    But we don’t sell junk. [Jerry]’s CRT was selected for its unblemished phosphor, and for its still-bright and vibrant performance. And, of course, there is the standard warranty of 1 month for a used CRT:

    But the question often comes: “How long will a CRT really last?”

    Here at Oscilloclock we don’t mince words, and we don’t use euphemisms (much!). But the fact is this – after 15 years of crafting Oscilloclocks for customers around the globe, no-one has reported having to change their CRT. Maybe it’s happened and we are oblivious. Even better!

    Our secrets to CRT longevity are:

    1. We select only the highest quality CRTs, made by reputable manufacturers. [Jerry]’s CRT was manufactured by Toshiba, a key supplier of the day.
    2. We check CRT specifications carefully, and avoid those with any hint of short lifetimes. (Some CRTs had very short expectancies, such as 1000 hours! Perhaps these were used for demanding applications where even a tiny degradation in performance could not be accepted.)
    3. Oscilloclocks employ multiple mechanisms to avoid screen burn-in (phosphor burn).
    4. Oscilloclocks employ a soft-start mechanism to minimize stress on the CRT heater.

    The Spare

    Notwithstanding our facts around longevity, [Jerry] decided to plan ahead for an eventual CRT replacement. He purchased a stunning new-old-stock Hitachi 3KP1, with quality certificate and even in its original box.

    They don’t get more original than this!

    But is a Hitachi 3KP1 better than a Toshiba 3KP1?

    We’ve compared them, and couldn’t tell any difference in performance or characteristics. We did notice one thing, though: the Hitachi is significantly heavier than the Toshiba. Hmmm….

    One day, we’ll dissect some (defunct) units, and get to the bottom of that odd observation. Stay tuned for a post!


    Like what you see? [Jerry] did. Check out our other creations!

  • Some time ago, [javadesigner] asked something that no doubt many of you have been wondering: Do Oscilloclocks emit radiation?

    Had a question about oscilloscopes – specifically cathode-ray tubes (CRTs). X-rays etc were discovered in similar tubes, and I’ve read that high kV tubes produce both beta and X-ray radiation.

    … Have you ever measured x-ray emissivity with CRTs, and if so, are there any mitigation strategies – especially for X-rays? Leaded glass enclosures, etc.?

    Great question!

    Will your faithful Oscilloclock do this to you?
    CRT used in this demo: 130BFB31

    Fortunately the answer is a clear NO. Our hand-crafted Oscilloclocks do not emit dangerous radiation.

    The general rule of thumb with CRTs (in fact, any electrical equipment operated in a vacuum) is that X-ray emission is negligible at anode voltages less than around 10kV. The accelerated electron beam simple does not have enough energy to generate X-rays when striking the phosphor screen.

    But above 10kV, X-rays can and are produced as a result of the higher-energy bombardment. The high-voltage CRTs used in television and computer monitors of the day always incorporated lead glass (strontium-barium glass), to block these X-rays. (And… to protect against implosion!)

    In any case, all Oscilloclocks operate at voltages well below 10kV, so this does not become an issue.

    A few of the CRTs in stock - 6498, D4P, 3WP1, 50SB1, CV2302. None emit X-rays!
    Just a few of our CRTs in stock – and none of them emit X-rays!

    Thats right – whether we craft your custom timepiece from a behemoth 6498 (at left, operating at 6 kilovolts), a delightful D4P (3kV), a sleek 3WP1 (1.5kV), a cute 50SB1 (1kV) or an eentsy-weentsy CV2302 (500V), you’ll be illuminated but never irradiated.


    Fascinated by electron beams and phosphor bombardment? Do you have a question that everyone else wants to ask? Query away, we love Q&A!

  • New stash!

    These beautiful vintage British* CRTs have travelled the world over the last half century. And like homing pigeons, they have found their way at last to the Oscilloclock Lab!

    From left: SE5F/P31, DHM9-11, E10-12GP, SE4DP31, SE5F/P7. Brands: Brimar, GEC, Valvo

    Here, each piece of glorious glassware will receive the attention they have craved for years. They will be cleaned, rejuvenated, and start their latter-day lives performing retro electronic miracles for loving new owners from all over the world.
    * In fact, one of these CRTs was not made by a British manufacturer. Can you spot which?

    From Unloved to Loved

    This SE4DP31 is brand new, complete with protective paper sticker that was attached at the factory to protect the front glass. It’s never been loved. Such a waste, and we will certainly rectify that, as we have done previously for similar CRTs:

    Two is better than One

    These bad boys are dual-beam CRTs. They have two electron guns and two sets of deflection plates, meaning they can display two completely independent figures at the same time.

    We used one of these in the custom Aftershock Clock, to overlay standard clock faces against a map hewn entirely from Lissajous figures. The intensity (brightness) and positioning of each beam can be independently adjusted to get the overlay effect just right!

    But importantly – the innards look so cool!

    Feeling Blue?

    We’ve talked before about rare blue phosphor finds. The newly landed Brimar SE5F/P7 will one day boast both presence and persistence:

    With thanks…

    We dedicate this post and the promise of seeing these CRTs reincarnated to [Atif]. Many thanks for helping these pigeons find their roost!


    Are you in a state of cathode-ray rapture? Check out other CRT related posts, and see the Gallery to see examples of vintage glassware objects given new leases on life!

  • Zork on an OscilloTerm!

    Today’s story began with a mail from [Eric], who’d read up on the Oscilloclock 3-inch VGA Assembly and wondered if it could be used to create an old-school serial terminal display on a vintage oscilloscope CRT.

    Yes it could! In fact, the Oscilloclock Lab did one better. Instead of just a VGA display controlled by an external device, we developed native terminal firmware that accepts DEC VT52 compatible commands over a serial port, and renders all text and graphics using beautiful, curvy Lissajous figures.

    The stuff of dreams. The OscilloTerm Exo B7S4.

    Demonstrating basic terminal features, connecting to a PC via serial cable
    Oh, did I mention? It’s a clock as well!

    Zork, anyone?

    Ultimately, [Eric] just wanted to play Zork. And together we made it happen.

    The CRT. The Case.

    [Eric] wanted a sleek ‘skeleton’ look. His choice of a gorgeous B7S4 CRT, mounted in custom-machined cast acrylic supports, exposes all glassware and allows for a titillating rear viewing experience.

    CRT rings and supports – originally introduced for the Oscilloblock “Summer Dusk” edition

    And with a high-transparency cast acrylic case housing the electronics, the OscilloTerm Exo can be enjoyed from every angle!

    Astute readers may wonder about the 2.1 kilovolts of high voltage coursing through their innocent-looking device. Rest assured! All internal wiring is sealed off, and Oscilloclock CRT harnesses are hand-crafted with heavy insulation and precautions taken against dust, prying fingers, rats, and even salivating cats.

    An O-ring blocks dust from entering the CRT/socket gap (picture from the Oscilloblock)

    This case and CRT mounting variation is branded the Oscilloclock Exo, and has proven its wow-factor at several public exhibits to date. We certainly love it, and [Eric] did too!

    The Terminal.

    This post would never be complete without showing you what real serial terminals from the 1970’s looked like, and explaining what they actually did! Here goes…

    Terminals such as the above were physical input/output console devices, back when computers were the size of massive refrigerators, and the operator would sit remotely – at a desk in a separate area, or even a different room.

    Gregory Lloyd, CC BY 2.0, via Wikimedia Commons

    The terminal and the remote computer were connected via a cable, and would communicate each other by sending data back and forth across the cable; mainly terminal commands and ascii encoded text. Most commonly, a serial communication protocol was used to get the data safely from one end to the other – and hence the devices were known as serial terminals or even serial consoles.

    Amusingly, they were also called dumb terminals, because they had no computing power of their own; they were only extensions of the computer to which they were connected.

    The OscilloTerm Terminal.

    [Eric] wanted a special Oscilloclock that he could also operate as a terminal, connecting it to a remote computer via cable. The remote computer would control the display, using the same serial protocol and commands as an ancient dumb terminal.

    But an Oscilloclock is anything but dumb. [Eric] wanted to keep all the standard exciting screens and features of his Oscilloclock active, and only display the special Terminal screen when the remote computer started to send commands. Then, when the commands stopped, the Oscilloclock should go back to the screen it was on!

    His wish was our command! Here’s a demo of smart screen switching in the final product:

    Some technical Comments

    Naturally, the terminal emulator firmware was written entirely in assembly language.

    PIC18F2680 – the Oscilloclock workhorse.

    We use assembly mainly because the minimalist PIC microcontroller used in the current Control Board revision has only 64K ROM, and an unbelievable 3328 bytes (yes, BYTES!) of RAM. To squeeze all the lovely Oscilloclock features in, while driving Circle Graphics real-time processing, the code and memory space has to be clean, tight, and heavily optimized at the machine code level.

    Assembly. It’s the ONLY way to squeeze it all in!

    For even more technical details, such as the list of VT52 (and VT100) commands supported by the OscilloTerm, and the various configuration parameters that can be tweaked to make the terminal emulator more ‘friendly’ when connecting to a specific device, check out the Support page. Worth a visit!

    Why Zork? And HOW?

    Zork is an interactive adventure game. But it’s old. And it’s text-based, because it was run on computers long before fancy graphics capabilities were widely available. The player explores mysterious locations, solves puzzles, and collects treasures while avoiding various hazards and creatures. All by reading text and typing commands and responses!

    [Eric] was able to play Zork by loading the game’s Z-code into a Z-machine interpreter known as Frotz, on a PC connected to the OscilloTerm. But there was trickery involved!

    1. He had to recompile a version of dfrotz (the dumb terminal version of frotz) to remove the status bar and audio from the game.
    2. He needed to wrap the dfrotz output with a custom Python script to support the OscilloTerm’s 16×8 screen and simulate the required baud rate.

    But now that’s done, he can play any Infocom game that runs in dfrotz on his OscilloTerm!

    What’s next?

    Readers would probably agree that adding a generative AI feature would be incredibly cool. For example, the War Games feature is great, but the text on the screens is all pre-programmed. What if you could interact more naturally with your Oscilloclock?

    Another one for the list!


    Are you a serial serial terminal collector? Do you want to play Zork on the oddest device imaginable? Or, you fancy a clock in the Oscilloclock Exo range? Contact us and let us know!