Digital Clock made with discrete Transistor/Diode Logic

[State Machine]

I have always had a fascination for time pieces. Especially for electronic ones designed using digital logic. I had worked part time as an engineer and designed in a "smart clock" digital timer and clock module for a garage door opener system using a microcontroller and a few hundred lines of assembly code and even though I use these modern methods, I still am fascinated with design methods of yesteryear. Continuing my fascination with digital time pieces early on in my career, many years ago I designed a digital clock using bunch of MSI TTL logic IC's which were all crammed onto a 4" x 6" vector prototype board. I am a sucker for anything nostalgic and the latest offering by "Nuts and Volts" magazine really sucked me into this one and I ended up purchasing the kit today that they offer on their store

The feature article in the new July 2009 magazine describes a 12 hour format digital clock that is designed using what is considered a very old and outdated logic by today's standards ...... diode/transistor logic.

Why bother doing anything like this you ask? Well doing a clock design with nearly 200 transistors and over 550 diodes is no small feat, and, it really gets you thinking of just how a toggle type or "T" flip flop (TFF) "really" works using crossed coupled BJT transistors and current steering diodes to facilitate the toggle action. Or how to design a transistor based comparator with hysteresis or wave shapers. It gets you thinking "inside the box" and gets you past that "black box" mentality. Of course, you would be laughed out of your design department using this methodology and normally you would be using integrated circuits or programmable logic for your designs BUT for hobby purposes and understanding logic circuits at the transistor level, you can't beat these sorts of projects.

Some early computers that used this very logic design technology were the Philco 212 shown below and the IBM System 360 series. Also, don;t forget the TX-2 computer, and the sketchpad drawing programs, that was built using discrete transistor/diode logic circuits, at Lincoln Labs. It really was a precursor to modern CAD drawing systems.

What next? Well, going even further back, how about a digital clock made with vacuum tubes? I am not willing to go that far but it really makes you appreciate ENIAC or Joniac series of mainframe computers with 1000's of tubes!!! The ENIAC computer, used flip-flops composed of vacuum tubes enabled the first computer to represent numbers electronically.

Here are the links to the N&V project ...

http://www.nutsvolts.com/
http://store.nutsvolts.com/product.php?productid=16868&cat=0&page=1

Bill

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[Inventor]

Bill,

They taught us DTL in school briefly for historical reasons, interesting project.

I made a clock for my master's thesis. It was a ring oscillator extended into a mesh form. The idea was to lower clock skew so faster processor speeds would be possible. The idea never took off but it was interesting. Provided multiphase clocks across the chip with distributed aggregation. Tick Tock goes the clock!

Les

[iceowl]

I've built 3 or 4 of their Russian Nixie Tube clock kits. Every time I finish one and put it in a nice case and set it up in my house, one of my relatives scams it from me and I have to build another one.

It's an easy build. The design is somewhat of a digital "cheat" -- uses a PIC to generate the timing pulses & state. Everything else is analog (would have to be).

But there's nothing quite as fun as a couple hundred volts on a tiny circuit board without any accompanying cussing, smoke, and sparks.

Now this kit sounds like just the sort of : slam-your-head-into-the-wall-as-hard-as-you-can project that warrants extreme investigation. 1200+ parts to do what you could reproduce in one 8-pin IC - well, I agree with the cover of the magazine. It is a terminal force that cannot be resisted. I'm pulling out my credit card as we speak....

[andrewF]

all tube clock?
you could do one of these -


here

[State Machine]

Thanks for the comments guys ....

Here is the technical manual for the transistor clock in case anyone wants a closer look at this project.

Here is the website for KABtronics in case you want a look at their other items.

http://www.kabtronics.com/index.htm

It's also worth noting that a NIXIE tube version of this clock will be released sometime in the future by KABtronics. It probably would not be much of a stretch to modify the current kit by adding an outboard power supply and NIXIE display and just tapping off the 4-to-10 decoder outputs to drive the NIXIE displays. This way you could have both 7-SEGMENT LED displays AND Nixie displays showing off the two technologies.

Here is the link to the IN THE LAB feature of the website:

http://www.kabtronics.com/index_files/Page367.htm

Bill

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transistor clock manual.pdf
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[Tasmanian Alkaloid]

[State Machine]