VGA display… On a 3″ scope tube!

Yes, you’ve all thrown away your lunky old CRT monitors, in favour of sleek ultra-thin LCD displays. And, you thought you’d never see another one again…

But this CRT display has a twist! It’s round. It’s small at just 3 inches diameter. And it’s awfully cute.

Oscilloclock 3-inch CRT VGA Display Assembly - overview

Last year, I was approached by a dedicated flight simulation enthusiast, who needed a radar indicator to use in a fighter cockpit replica. The indicator should employ a CRT, for the most realistic look. Could Oscilloclock design and construct such a display?

It didn’t take much convincing! Diverging only temporarily from building clocks, I took up the challenge to create my first raster-scan CRT display unit. In the ensuing months, difficulties sprang forth from every direction in the project, but ultimately I was able to avoid a diraster (sic) and deliver a functional assembly:

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The Setup

The key component of this setup is a new prototype VGA Board that converts a VGA signal into analogue X and Y outputs. Both analogue intensity and binary blanking outputs are provided.

Oscilloclock VGA Board prototype

Oscilloclock VGA Board prototype

The X and Y outputs drive an Oscilloclock Deflection Board, while the binary blanking output drives the blanking amplifier in a CRT Board.

Oscilloclock Deflection Board - modified for ultra-linear HV output

Deflection Board – modified for ultra-linear HV output

CRT Board - heavily modified for improved frequency response

CRT Board – modified for improved frequency response

Blanking isolation, heater, and HV supplies are provided by a Power Board.

Power Board - with improved optocoupler

Power Board – with improved optocoupler

It all looks so easy! But noooo. Astute readers will recall from other posts that every Oscilloclock project involves sleepless slumbers, horrific hair-pulling, and forgotten family members. Let’s see what caused me grief this time…

Challenge: How to get a BRIGHT raster scan?

TVs and monitors use raster scanning to display images. The electron beam moves continuously and rapidly across the screen in a predetermined pattern, while the beam is turned on and off at the right locations to generate an image.

This is actually quite bad for me.

To see why, pretend you are a graffiti artist, painting a circle on a wall. Normally, you would just move your arm in a circle, and paint. This is effective. You could get a thick circle in just one or two iterations.

Now instead, try a raster scan: move your arm across, back, down a little, across, back, down a little, across, back, … , and press the paint button at just the right places to draw bits of the circle. Your circle will start out very light, and it will take you many, many iterations of the raster scan to get a nice dark circle.

Graffiti circle sprayed normally (left) vs. using raster scanning (right)

Graffiti circle sprayed normally (left) vs. using raster scanning (right)

The CRT is just like your spray can: the electron gun streams electrons at a limited rate. If the beam is moved in a fast raster scan pattern, the number of electrons hitting a given spot of the screen at once is limited, and this limits the brightness of that spot.

The brightness vs. DEFLECTION trade-off

To offset this limited electron flow, CRTs in real computer monitors apply a very high voltage (often 10-20kV for monochrome monitors) as post-deflection acceleration (PDA). After the beam is deflected, the electrons are greatly accelerated by this potential, and they smash into the screen with incredible force. The sheer speed of the electrons offsets their small number, and this creates an immensely bright spot.

Unfortunately, most of the cute 3″ CRTs available in quantity today do NOT have this post-deflection acceleration. Indeed, the customer hoped to use the general-purpose non-PDA type 3RP1A, as it is widely available. But a raster-scanned image on this tube would be quite faint. And to make matters worse, the customer required a bright trace even with a green-colour acrylic filter applied!

The constraints here did NOT look promising. But I rarely give up.

I decided to configure the Power Board to deliver 2kV to the deflection plates, which is nearly double what most circuits supply for this tube. This would forcefully accelerate the electrons to a great extent; maybe even enough to get a bright trace?

But there is always a catch! Without PDA, the beam gets accelerated before it exits the deflection area. Due to electron inertia this means that the beam can’t be bent as easily, and the image gets smaller. To offset this, a much larger signal is required to deflect the beam sufficiently to reach the edge of the CRT screen.

Could my poor Deflection Board deliver a signal with enough magnitude?

Reflecting on Deflection

Let’s review the 3RP1A’s specifications below, and see just what is needed! Running at 2kV, and taking the worst end of the range, the X-axis deflection plates (“Deflecting Plates 1-2″) require a whopping 198V signal to deflect just ONE inch from centre!

Sylvania 3RP1A typical operating conditions

For our 3″ screen, we need 1.5 times 198 = +/-300V (approx), to deflect the beam from centre to either edge of the screen. So far this sounds fine; the then-standard Oscilloclock Deflection Board could just barely deliver +/-300V before losing linearity.

BUT it turns out we actually need to deflect more than 1.5″ from centre!

Take a look at the diagram below of the raster image I wanted to display, as it appears via an 800×600 VGA signal. See how much dead space there is, particularly at the left and right sides? This space is specified in the VGA standard as sync pulse, front porch, and back porch timings, to allow time for the display circuitry to prepare for processing each line.

VGA overlay showing dead space (timings courtesy

VGA overlay showing dead space (timings courtesy

A further complication (can there be more?) is that we want to display a circle in 800 x 600 (a 4:3 aspect ratio), on a round screen (a 1:1 aspect ratio)! After converting all the above dimensions into a 1:1 aspect ratio, and expressing in inches for convenience, we arrive at this:

Aspect ratio changed to 1:1 and converted to inches

Aspect ratio changed to 1:1 and converted to inches

And THUS we conclude that the beam must travel a maximum of +2.525″ to the right, and -3.325″ to the left, to make the actual radar image’s circle travel +/-1.5″ and touch the edge of the screen. And a -3.325″ deflection on the X axis (“Deflecting Plates 1-2″) at 198V/inch equates to no less than -658V ! Oh, my poor, poor 300V Deflection Board…

Stuck – But NOT beaten!

After hours of fretting, I hit upon a brilliant idea. Here are the facts:

  1. Looking at the VGA diagram, most of the dead space is in the X direction. The Y direction has very little dead space.
  2. Looking at the CRT specs, the deflection is more sensitive at “Deflecting Plates 3-4″ than at “Deflecting Plates 1-2″. This is because 3-4 are closer to the electron gun than 1-2, and at that location the electrons are moving more slowly.
  3. Because the closer plates 3-4 are more sensitive, nearly all oscilloscopes apply the VERTICAL signal to these plates. And blindly following this convention, I, too, was planning to assign the Y output to these plates.
  4. BUT in a VGA display, neither vertical nor horizontal signals are high frequency! And, the two signals have the same amplitude (0-5V), so deflection sensitivity doesn’t really matter.

So wow! Hang convention -  Why not apply the troublesome X output, which needs way more deflection than Y in order to overcome the dead space, to the more sensitive plates 3-4? And then simply rotate the tube 90 degrees!

Let’s do the math again…

3.325″ deflection on the X axis using the more sensitive (“Deflecting Plates 3-4″) at 140V/inch equates to -466V! This is a fantastic improvement over -658V. But it’s still much more than the +/-300V my Deflection Board could deliver….

Healing the Deflection Board

Oops – I’ve run out of space for this post – and you, dear reader, have run out of patience.

Keep your eyes pealed for Part 2 – where we’ll take a look at the basic circuit of the Deflection Board, try to understand WHY it wouldn’t track more than +/-300V linearly, and finally see how I resolved the limitation. Challenge after challenge after challenge!

From the Archives – a 400-LED Oscilloscope

Long, long ago… In a workshop far away…

Recently, I’ve seen quite a few search hits and even an enquiry regarding the 400-LED dual-trace oscilloscope that I briefly mentioned on my History page. With renewed enthusiasm therefore, let’s take a trip down history lane and see what I was doing back in 1990!

A compact dual-trace 1MHz DC scope - what more could a high school kid want?

A compact dual-trace 1MHz DC scope – what more could a high school kid want?

This scope even has a Fill mode. Castles anyone?

This scope even has a Fill mode. Castles anyone?

Lots of controls for such a tiny case...

Lots of controls for such a tiny case…


Subject: Dual-Trace Oscilloscope Design and Construction
Period: 7/90 – 10/90
Submitted to: Mr R. Young, Physics Department
Project Designed and Constructed by: [Aaron] (present-day


When students studying Grade Twelve Physics began a unit on Electronics during the third term of the year, I became increasingly involved with the apparatus used by the teacher, Mr. R. Young. As I was already familiar with most of the material set out in the unit, I often helped Mr Young construct test circuits and/or set up equipment as teaching aids. In this context, I soon came to know the oscilloscope to a great extent. Having been an electronics hobbyist for the last twelve years, I was well aware of the functions of the oscilloscope, and to use it quickly became second nature to me. I was amazed at the detail of the information which the instrument gives the user about a circuit, and felt inclined to construct my own.

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Tek 520A VectorClock!

Television broadcasting has switched from analog to digital - and if you’ve got a nice HD TV, you’ll be loving it!

But with that transition came the death of an entire breed of equipment – the Vectorscope.

Tektronix 1420 Vectorscope

Just to be clear, these are not monitors for playing ancient video games using vector graphics!!  No, the Vectorscope is (was) used to give a delightful view of the ‘vectors’ inside an NTSC or PAL video signal, describing the color components of the signal.

If you were lucky enough to be a TV broadcast technician, you’d use your Vectorscope all the time to check your vectors’ amplitudes and phase. You would even give your vectors names like ‘Jack’ and ‘Jill’, and check up on their relationships daily, just as any responsible guardian would!

But above all, you would marvel every single day at the beautiful hardware you were using, and the complex circuitry involved. Take a look at my Tektronix 526 Vectorscope, which has oodles of delicious tubes to heat my shop on a nice winter’s day:

Tektronix 526 Vectorscope

Well, it all went digital and there is no longer any need for analog color signal analysis. But dry your tears… There is something even better:

Announcing the Tek 520A VectorClock

This lovely Oscilloclock reincarnation of a Tektronix 520A, sold at Maker Faire Tokyo 2013, allows its new owner to forever relive the magic of NTSC, PAL and SECAM analog color.

Tektronix 520A VectorClock - brilliant blend of the old and new!

Tektronix 520A VectorClock – brilliant blend of the old and new!

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The Tektronix 520A has a stunning built-in array of lights for illuminating the CRT graticules. By simply removing the bezel and external graticule, the Tek 520A morphs into a deliciously moody timepiece!

Tek 520A VectorClock - Glorious Glow

Normally, I shun CRTs with built-in graticules. Their lines detract dreadfully from an Oscilloclock image. But here! The Tek 520A’s internal vectorscope graticule is round! What better way to accentuate a Circle Graphics driven display?

Silky smooth Circle Graphics on steroids!

Silky smooth Circle Graphics on steroids!

Under the Cover…

The Tek 520A is solid-state. It can be left on 24 hours a day and not fail for many years. This makes it a perfect match for my Maximum Re-use + Minimum Invasion policy: nearly all existing circuits – HV power supply, deflection amplifiers, blanking – are put to use, with just a few (reversible) tweaks.

Tek 520A VectorClock - Maximum re-use, Minimum invasion

The Oscilloclock Power Board is mounted neatly next to its own dedicated low voltage supply. A small relay board can be seen below, for controlling the Tek’s main power unit. All cabling is HV-tolerant and neatly fastened with high-temperature cable ties.

Tek 520A VectorClock - Control Board mount and cabling

Of the more interesting reversible ‘tweaks’ needed for this retrofit, here we see a delightful little trimpot pretending to be a transistor. Quite an act, I would say!

Tek 520A VectorClock - an unorthodox transistor replacement

Like what you see?

If you love big, looming Vectorscopes and need to have one put to good use in your living room, Contact me. And be sure to subscribe from the front page, to track all the other exotic experiments and unique timepieces targeted for 2014!

Credits to [Quinn] in Canada, for providing the initial inspiration for the Tek 520A VectorClock project!

Santa in your Clock!

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

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

Beam me in, Santa!

Beam me in, Santa!

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

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Luxury 2013 edition Model 1-S!

This 2013 edition hand-crafted scope clock exudes sophistication and elegance, to match the most refined interior – be it the boardroom or the bedroom. The 1-S boasts solid brass fittings custom-turned in Japan, ultra-transparent cast acrylic housings, and a decadent harness with chrome connectors and gold-plated pins from France. The brand-new old stock CRT was selected especially for its gentle white-blue trace and extremely long persistence, to provide a relaxing and refreshing viewing experience.

2013 luxury edition Model 1-S scope clock from

This particular unit went on display at Maker Faire Tokyo 2013, and was sold within several hours. Enquire via the Contact page for pricing and availability of the Model 1-S and other exclusive Oscilloclocks.

See more related videos on my YouTube channel

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Oscilloclock at Maker Faire Tokyo!

Summer is over! But even as cool weather sets in, the lab is smoking hot, preparing for…

Maker Faire Tokyo 2013

Visit the booth, and check out the luxury 2013 edition Model 1S – to be announced in this blog at end October. One unit will go on sale at the event!

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Making the Heathkit Oscilloclock

Last month’s post about the Heathkit Oscilloclock generated tremendous interest, and I’ve heard from several folks keen to try their hand at preserving their own beloved instruments.

… so let’s take a brief look at what was involved in the Heathkit OR-1 conversion!

Heathkit Oscilloclock - inside

Approaches to conversion…

There are many approaches to retrofitting a scope into an Oscilloclock, but it really boils down to how much of the original circuit you want to re-use, vs. what you will bypass with Oscilloclock boards.

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A Heathkit Oscilloclock!

Anyone familiar with Heathkit®?

From 1947 to 1992, the U.S. based Heath Company produced electronic kits for everything you can imagine: radios, TVs, computers, robots, ham gear, and electronic test equipment. Yes, you guessed it – they also produced kits for oscilloscopes!

My Grandpa purchased one such scope, the Heathkit OR-1, around 1960. He wanted to kick off a new career in electronics repair, and the ‘build-your-own-equipment’ approach to training was in full bloom at the time. Also, since this was before the era of cheap overseas manufacturing, he could buy a Heathkit far cheaper than an assembled scope.

Heathkit OR-1 manual - a work of art

Heathkit OR-1 manual – a work of art

Unfortunately, Grandpa’s electronics career never really took off. But decades later, he introduced me to his gorgeous oscilloscope, and boy – did that kick MY career off! Much later, the OR-1 came to live with me. (You can read a bit more about my affinity for this scope in my History page.)

The problem is, I have too many oscilloscopes. But I don’t have enough Oscilloclocks. What more fitting way to keep Grandpa’s legacy alive, than to retrofit his Heathkit?

Heathkit OR-1 Oscilloclock

Heathkit Oscilloclock - Splash and Clock

Special features

Circle Graphics (see my earlier post) makes for smooth, graceful characters constructed entirely from lissajous figures! Never before has an oscilloscope looked so utterly delightful.

Heathkit Oscilloclock - circle graphics

The horizontal sweep frequency fine adjustment knob, conveniently located smack in the middle of the front panel, functions as the single control for the Oscilloclock. (A video showing what this control does is up on my YouTube channel.)

Heathkit Oscilloclock - single control

Eventually I might make an acrylic case, to show off not only the CRT but also Grandpa’s soldering prowess. In preparation for that, I’ve made sure that all the tubes (valves) still light up when you turn the original power switch on. What a beautiful scene!!

Heathkit Oscilloclock - tubes lit

The 5ADP2 CRT in the OR-1 is decidedly unattractive compared to other tubes I used in the Model 1 and the Prototype. It is also technically inferior, not having post-deflection acceleration. However, it has one redeeming feature – a P2 phosphor! This phosphor gives just a hint of blue, and it has a simply divine after-trace of just the right length to create soft, flowing figures while still maintaining reasonable sharpness and clarity. (Visit my earlier post for more info on the phosphorescence phenomenon!)

Heathkit Oscilloclock - P2 phosphor persistence

The Oscilloclock boards are mounted on attractive acrylic back-planes and are easily accessible from the side and top. Image size and position adjustments can be made with the case on. The case can be easily removed to reprogram the clock:

Heathkit Oscilloclock - programming

The OR-1 happened to have a trimmer control at the back, so I tucked this control inside the unit, leaving a nice big hole – perfect to mount the socket for the Garmin GPS unit. This baby never loses track of time!

Heathkit Oscilloclock - GPS socket

Like what you see?

If you have a cherished oscilloscope that you wish to preserve in entirety, but also want to put to practical use in your workshop, office, coffee shop, or museum, converting it to an Oscilloclock is a nice idea!

However, the conversion process depends heavily on the oscilloscope you have, and your preferred approach. There is no single ‘cookie-cutter’ step list, although the Oscilloclock boards are designed to be relatively flexible. In the next post, I’ve highlighted the key steps taken in converting the Heathkit OR-1. Take a look!

Lastly, a note regarding Heath Company: As far as I can tell from their web site, they are in business again, and are even planning to re-start kit production! They of course own the Heathkit logo and trademarks referred to in this article. It is my hope that rendering their logo on the Oscilloclock will not offend them.

Transformer Corner part 4

Winding your own HV Transformer

In Transformer Corner Part 3, I looked at how to choose materials for a custom HV transformer. One way was to pull stuff from the junk-box – I did this in my early Prototype. The much, much better way was to use an off-the-shelf core with documented specs.

Let’s look at winding up the transformer. It’s amazingly easy to get a workable result!
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Transformer Corner part 3

Designing your own HV Transformer

In Transformer Corner Part 2, I looked at the power supply used in my early Prototype, and showed how to determine the key requirements for the HV transformer.

Now, let’s see how I could choose the materials and design the transformer – without any pesky mathematical formulae!

A hand-wound HV transfomer!

The end goal – a hand-wound HV transfomer!

Picking a core

The first challenge was to find a suitable core from my junk box. First off, recall from Part 1 that this couldn’t be iron (too ‘slow’ for 151 kHz), and it couldn’t be air (too ‘weak’ for 25mA). I suppose I could have tried plastic, milk, or even beer – but I knew better. I knew about a substance called Ferrite.

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