A Countdown Clock With LEDs


Introduction: A Countdown Clock With LEDs

About: I'm an Engineer, who originally inherited the family business (Thanks Dad (RIP JC Taylor, 1938-2011)) after working in it for 25 years, designing and building scientific instruments. In 2013, I was head-h...

These are some brief notes about a 'Countdown clock' I built 10 years ago for Y2K, The clock is 4 feet square from the front. It is about 4 inches thick, and runs on an embedded microcontroller. Each Segment is made from around 20x 10mm LEDS.

I can't take a picture with it on, because it is WAAAY too bright !

The panel was carved from a template I made for an ordinary router, with an extended template following cutter. I made the template in hardboard (fibre board US-ian ?) and just carefully aligned it with marks on the panel to cut it out.

Laying out the second Leds was more of a bitch than I expected - do the math carefully to pitch them PERFECTLY.

Step 1: A Digit

Here's a view of the back of a segment. I used the classic LM317 constant current circuit to drive each bank of LEDs.

The drivers for the displays are done with serial-to-parallel converters which seem to have been replaced with these things:

...these new parts will do all I did then with the 317 as well - a complete LED driver in one chip. Only a single resistor sets the brightness for all the leds !

Each digit is driven by that chained ribbon cable, which carries all the common signals for these chips, Vcc, GND Clock, Latch Enable and output enable. So there are only 6 wires leave the computer for ALL the segments of ALL the characters AND the 60 second LEDS round the edge. Each drive chip though has one unique line( the pink wire) that daisy chains through the whole system. The display looks like a very long shift register - see diagram below

An update for the display takes a very tiny fraction of a second.

Step 2: The Microcontroller.

I absolutely love the 8052 microcontroller, its second sourced and tweaked by just about everyone. A professional user, can even download VHDL code to implement one in an FPGA, and tweak the whole core to drive any weird hardware I care to conceive.

Makers include Atmel, NXP and WinBond.

Development tools are dead cheap, there are free assemblers and free 'C' compilers (SDCC) too.

I actually programmed this entirely in Pascal with a piece of assembler code specially written to do the display update as fast as possible. At some point I'll post the code too.

This is the controlling computer. The CPU is a called a Dallas DS2250T, and it came as a little SIMM card style board containing 32K of battery backed RAM, used for programs and 8K of RAM for program data use. The big 40 pin chips are more Serial to parallel chips for the second LEDs.

Beneath the 40 pin packs is an LS125 line driver chip, to drive the ribbon cables.

The white connector at the top was for a set of push buttons for setting the clock.

Step 3: Software Notes

I wrote a simple piece of PC code to work out exactly how many hours there were in any interval between when you wanted the countdown to start and "zero hour",

The embedded program just tested its internal clock every second and decremented the display. Every minute, all the Leds lit up, and gradually turned off until you reached 60 again.

There is a little pushbutton panel for setting up the display, just like an alarm clock.



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    25 Discussions

    Hey "steveastrouk" di you ever make a video or a new diagram for this clock? I want to make one for the 2012 countdown just for a joke around here but I am a very new novice on these things.

    If you did or if you can make a diagram and or a video with the up to date way could you please email it to me through this site that would be awsome for me.

    This I really would like to make.

    Thank you

    9 replies

    I've got the design of the segments nearly ready to go - driving them can be done with any flavour of control you like.


    Hi Steve, I bet you don't remember me but I sent you a couple of messages about 6 years ago about this LED countdown clock and you were supposed to send me the design of the new segment and a few other things. I did the same thing that you did I forgot all about it until now when I was going through my comments and questions and ran across your post again...LOL I am trying to get into learning how to code and Arduino's and things like that more now that I have more time. I was wondering if it would still be possible if I could still get all that info? I have been trying to find the best info that I need to learn how to code the quickest and easiest way but I cant even figure out what is the best program to use to run the code and even how to get it. I really want to get into LED's so much that at the moment I am trying to put together a LED Markee and I have the array build but I am stuck at finding the program to use to start the code.

    Ok I think that's about it for now I just thought that I would send you a note to see if we could still do this. Sorry about the book righting but thanks again for your time and I hope to talk to you soon.


    Thanks Steve for replying back to me.

    I would like to put one together with the days,hours ,minutes, seconds and tenths 0f a second if that is the next in line, I am very tired right now I can't think straight right now so I hope you can under stand what im wanting to put together. I you have and questions please feel free to just ask anything
    you want.

    I am in the process of trying to put together the computer in a tool case. I have almost everything I need to do it so im trying it to see if I really can do it or not. This is my first time doing anything like this and if I can do this project it will boost me up so much and help me really help me get into this more and I will fell better about myself to try the clock that you have. I would really like that to be my neat project after this computer.

    If you don't mind I may need some help when I get to loading the BIOS so I might be hollaing at ya for a bit if you don't mind. and if you do mind thats ok to.

    Thank you for all you help and please send me the files or video when you get it done. I really want to get into LEDs so I think that one will be a fun project.

    Thanks again and I hope to here from you again soon.

    Just so I understand, your Instructable describes in outline form how you built this LED clock. The Instructable really does not give enough information for readers to build it, unless they already have some specialized background expertise. It is impressive and deserves a nice case for display.

    9 replies

    Sorry, its an aid for a guy who posted a question in the site forum rather than a blow-by-blow account of building it - 10 years ago ! Of course, if I knew then what I know now, I would have recorded in better.... If the interest is there, I can reverse engineer it, and post my circuit diagrams. Using the serially addressed LED drivers saves a hell of a lot of wire !

    I wanted to make one like this b4 y2K. if you finally do a reversed engineering, could you add more digits , like the seconds and tenth of a second count? please do provide the circuit drawings please please . thanks. great project.

    I've a further instructable on the way with the PCBs for the segments. Putting more digits on would be pretty easy.

    Thank you for the reverse engineering offer. It is beyond my knowledge base, unless there is a "for dummies" edition. I probably do not need one badly enough to get it done.

    Indeed - (I'm starting to sound like I want to marry an arduino) - An arduino would have plenty enough memory, program space, and speed to do a 42 segment + 60 led sign...It would need some sipo registers, or max led drivers... I want to build projects like this, just because...I can never come up with a reason why.

    Do it please Mr. Frollard. for better or for worst, i'd like to be introduced to an arduino mp. I heard they're easier to work with.

    ....the 8052's are cheaper and more functional.... Nothing like as trendy here though :-( Steve