What is The Fortress E1T Clock? It's the culmination of two like-minded individuals who like to tinker with vintage display technologies and turn them into functional time-pieces. This clock is unique in many respects. It is, to our best knowledge, the only "commercial" E1T clock offered for sale at this time. Others have offered PCBs etc., but this is the whole enchilada and as such is a rarity to be treasured and enjoyed. The Fortress E1T Clock is a combination of old-skool technology married with a very modern micro-controller and 21st century case construction and aesthetics. It offers lots of customisation options, such as different "faces", LED colours (bling), chimes, GPS or WIFI disciplined timekeeping and is also open source in its design philosophy.

What is an E1T tube?

The plethora of methods developed during the late 1940's to the 1970's for displaying/counting numerical information were numerous and varied. These included incandescent displays (e.g. edge lit displays such as those from Non-Linear Systems), neon gas based displays such as Nixie tubes and Dekatrons, vacuum fluorescent displays (VFDs), light-emitting diodes (LEDs) and liquid crystal displays (LCDs). Some of these possess a certain charm, such as nixie tubes and Dekatrons with their warm orange glow and others not so much. What makes the E1T stand out from these technologies is that it represents the adaptation of another vintage display technology, the cathode ray tube into a discrete counting device. The E1T uses a cathode ray and some neat tricks to display a green line in 10 positions, each cunningly numbered from 0 to 9. These were used in early counters, such as the one pictured here:

A far more detailed explanation of how to electrically drive an E1T can be found in the project documents. There are also some great resources on the web for history and data about the E1T.

Here's a complete Counter by Philips that uses five E1T tubes:

Although this webpage almost exclusively talks about the E1T tube, there should be no reason why the close clone or the E1T, the S10S1 made in East Germany, will not operate successfully as well.

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Describing the Hardware

The clock hardware is complex and we think comprehensive. We wanted to respect the rarity of these tubes by creating a first class clock to use them. The main elements of the hardware are:

The items marked * above are primarily intended to prolong the life of the E1T tubes although they may have secondary benefits such as reducing power consumption.

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Describing the Case and Cover Options

Build your own

The simplest case option is to craft your own design. The physical size and board layouts will limit what you can do. But the choice of materials is entirely your own.

Safety: If you have a metal case or exposed metal parts then you must electrically bond the metal to the clock's negative supply. There is a screw connector on the main board for this purpose.

Simple Acrylic Case and Cover

Currently unavailable

Premium Acrylic Case and Cover

Because the premium cases are made to order, please allow about 4 weeks from ordering to shipping.

The choice of acrylic colours is wide and includes translucent, frosted, mirrored, tinted, fluorescent as well as conventional colours. If the case sides are opaque to IR then an additional hole is cut in front of the IR receiver. The premium case has additional engraved elements and these can be filled with a choice of colours.

The costs presented on shop page are for a fairly typical selection of acrylic colours. If you plan something exotic then the costs may be higher …

Limited Edition Aluminium Case and Acrylic Cover

A case using black anodised aluminium sides is in development. The cover will be welded 6.35mm thick clear or tinted acrylic.

Likely timescale and costs are not available at the moment.

The case will only be available for fully built and tested clocks.

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Describing the Software

For the SAM3X8C

This is written in C using Atmel Studio 7 and the GCC ARM compiler. It makes extensive use of the Atmel libraries.

The source code is open. You can download the complete source code from the project dropbox together with compiled binary file. The binary is burned into the SAM3X8C using the external programmer and BOSSA flash programming utility.

Instructions for burning the SAM3X8C using the external programmer and, should you wish, compiling the source code are in the project documentation.

For the ESP32-BIN

The ESP32-BIN module uses compiled binaries from the ESPRESSIF website.

Instructions for burning the ESP32-BIN using the external programmer are in the project documentation.

For the MEGA16U2 (on the external programmer)

This is written in C using Atmel Studio 7 and the GCC AVR compiler. It is open source. It uses the Atmel and LUFA libraries.

The source code is open. You can download the complete source code from the project dropbox together with compiled binary file. The binary is burned into the SAM3X8C using the external programmer and BOSSA flash programming utility. The SAM module will normally be supplied fully assembled and tested with the latest firmware burned.

Instructions for burning the MEGA16U2 and, should you wish, compiling the source code are in the project documentation. The MEGA16U2 will normally be delivered burned with the latest firmware and the programmer partially built and partially tested.

About Nuggle

Ok, you are now thinking, what's a Nuggle?

What has a mythical creature from Shetland folklore got to do with the Fortress E1T Clock? I will explain some of the details…

Consider what happens when the clock is running:

Happenings or Events occur such as shown on the left … such as the clock ticks, the PIR senses motion and so on. The clock software must then decide what to do. So, for example, if the clock is currently showing the time in a hh:mm:ss format and the clock ticks one second then the E1T display will need updating, the clock colons, if flashing, will need their state changing and if a tick sound is played then that will need to be started.

In other words, given a range of Events, the clock software must Decide on what Actions to take.

The starting events are fairly few in number as seemingly are the actions to take. But when you consider that there are twenty one events for the IR handset (one for each key), there are about a dozen sleep states and six types of tick (second, minute, hour, day, month and year) the starting event list grows in size. The actions you can take for the chime sounds is to play any audio file on the SD card (so the number of audio files is only limited by the SD card capacity), the number of beeps (frequency, duration, stereo channel) is similarly a large number, there are 32 bling LED modules, each module can (in theory) display over sixteen million colours. Against these numbers the E1T tubes are much more defined with only eleven states to consider (0…9 and off) giving a mere sixty six options.

A common course would be to write code in C that handled a number of configurations where the actions taken for each event are programmed and burned into the SAM3X8C microcontroller. There is a disadvantage to this approach - editing or creating new clock configurations requires the source code to be edited, compiled, burned and then tested. It also makes the distribution of any new configuration more difficult. Therefore a different approach has been taken - to encompass the decision making process in a simple text script on the SD card. Here's an example:

program Time01 - Put hh:mm:ss on the E1Ts - Blank Bling ; customise the colour colour: Constant colon_colour 0x001000 Number Hr ; Called on start event_start: WriteLn "Time 01 - No bling" Default Stop ; Called every second event_tick: ; respect user's 12 or 24 hour time ; assume 24 hour clock to start- Hr := hour ; perhaps a 12 hour clock? If Low(fmt_time) == fmt_hr12 ; user wants 12 hr format? If Hr == 0 Hr := 12 Else If Hr > 12 Hr -= 12 IfEnd IfEnd IfEnd ; check leading hour zero suppression If Hr > 9 E1T 0, Hr / 10 Else If MidLow(fmt_time) == fmt_hh ; is zero wanted? E1T 0, 0 Else E1T 0, E1Toff ; not so turn off the E1T IfEnd IfEnd ; fill in the other tubes E1T 1, Hr % 10 E1T 2, minute10 E1T 3, minute1 E1T 4, second10 E1T 5, second1 ; flash the colons together If Odd(second1) Fill colon_colour, 1, led_colon Else Fill black, 1, led_colon IfEnd Transmit Default Stop End

The script "language" is a mixture of Pascal and C, and, for reasons that I'm going to leave obscure, I called it Nuggle. The text files on the SD card have a .NUG extension.

The example above does no more than display the current local time on the six E1T tubes. It does allow for the user time display preference (leading zero suppressing on the hours and 12 or 24 hour format). And it flashes the colon light guides each second. But it makes no use of the other light guides, no use of the chimes and it certainly does not beep.

The Nuggle language manual is available from the the project dropbox. Nuggle has a Fortress E1T clock supplement covering the Nuggle commands that are unique to this clock. The intention is that Nuggle will be extended to work with future Sgitheach clocks.

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About Open Source

One intent of the Fortress E1T Clock project from the outset was that the hardware and software would be fully open. The project documentation is held on a dropbox where you will find:

If I have missed anything from the list that I should be providing then rest assured that I will.

The 3D printed parts and other case components were designed in Fusion 360. Whilst the F360 files are not immediately available on the dropbox, I will provide them if asked. The reasons I don't immediately provide them is they are a bit of a faff to export from F360, that I suspect the demand for them will be low and they would represent yet something else to keep updated.

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The distribution centre for documentation specific to the Fortress E1T clock is available from this Public Dropbox folder, "/E1T Projects/Fortress E1T Clock", dedicated to the project.

A second folder, "Common Stuff", provides access to information that used by the Fortress E1T Clock but is also common to many other Sgitheach Projects:

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Fortress E1T Clock Kits have sold out!

Built and tested clocks are still available from Stock's Clocks.

N.B. None of these kits include E1T tubes - they are yours to provide or can be bought separately!

The prices of all these kits and E1T tubes are here.

Minimum Electronics Kit

This kit includes:

If you take this kit then I assume you know what you are doing! There are a lot of parts to collect. You need to be confident to be able to solder parts as small as 0603 and a LQFP100 part with 0.5mm lead spacing. You will need access to a 3D printer and be able to cut acrylic tubing accurately.

The photograph of the minimum kit shows 2x3 panellised GPS and WIFI plug in boards. You will receive only one …

Of course the real minimum kit is nothing at all - you take the Gerbers and get your own boards made and get the custom transformer wound yourself. The minimum kit here represents what I think is a more likely kit where I supply the bare PCBs and the flyback transformer.

Standard Electronics Kit

This kit includes:

The photograph of the standard electronics kit includes both the GPS and WIFI plug in components. You will only receive those you buy …

The SAM3X8C programmer board uses a ATMEGA16U2 microcontroller that must be programmed using a suitable AVR programmer. If you wish I will burn the mega for you for no charge.

Standard Electronics, Simple Case and Cover

In addition to the standard electronics kit above, the Standard Electronics, Case and Cover kits includes additionally:

  • 3mm and 5mm thick laser cut clear acrylic to build the cases for the clock and power supply
  • 3mm thick laser cut clear acrylic to build a dust cover for the clock
  • 3D printed parts used to joint the acrylic together, a knob, and cable gland
  • All the required nuts, bolts etc. to assemble the acrylic and 3D printed parts

Standard Electronics, Premium Case and Cover

In addition to the standard electronics kit above. The Standard Electronics, Premium Case and Cover kits includes additionally:

There is a wide range of acrylic colours you can choose from for the 3D printed parts, case and cover.

What if the kit you want is not listed?

In principle, I will assemble a kit containing the parts you request.

But I am reluctant to provide a kit containing all the SMD parts loose for several reasons. It takes a considerable time to bag and label all the SMD parts; a considerable amount of waste is generated by the kit purchaser when all the bags have been emptied. Unassembled kits I will normally fully refund (other than the postage) if returned. However, I cannot easily use short lengths of SMD tapes on my pick and place machine so I can only offer a partial refund.

Fully built?

Built and tested clocks are still available from Stock's Clocks.


The electronics kits and simple acrylic case and cover kits are shipped from Scotland. Postage will be whatever I have to pay and no more. A complete kit will normally be shipped with tracking and insurance. Outside of the UK shipping will be by air. Inside the UK shipped Royal Mail "Special Delivery" is normally used. I will give you an estimate for shipping to your location based on Royal Mail prices and then the actual cost when posted.

The Premium Case and Cover kit (with no electronics) are shipped from San Diego USA. USPS will normally be used.

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Please contact me with any questions or enquires about ordering or postage.

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Further Reading

Electronic Counting Circuits JB Dance 1967 Iffle Books Ltd.

E1T, from Dieter Wächter
S10S1 from Dieter Wächter
From Ronald Dekker and also on the making of the E1T.
An E1T Tester
Joachim Gittel (in German)
Elektor - registered users only
E1T Frank Philpise
S10S1 Frank Philpise
Philips PW4032 Counter
S11S1 HT Schmidt (in German)

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Acknowledgements, E1T Clocks and Testers, E1T on YouTube

Dieter Wächter
Ronald Dekker
Ronald Dekker on YouTube
Steampunk Alchemy - this link doesn't open correctly for me
Benadski on YouTube
KainkaLabs on YouTube
moelarryshemp on YouTube
MACBSD on YouTube
Armin Schoen on YouTube
Jens Pahl on YouTube
An E1T counting forwards on YouTube
An E1T counting backwards on YouTube
An E1T counting backwards - an oscilloscope's view on YouTube
Mike's Electric Stuff has a brief mention

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