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Electronics 7-segment LED Clock

Discussion in 'Modding' started by Explicit, 27 Sep 2004.

  1. Explicit

    Explicit New Member

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    I want a clock that's made out of 7-segment LED Displays, but blue ones instead of nasty green or red ones. Blue ones are available at Digikey.

    The thing is, the volatages are different for different collors, which isn't to big a deal.

    The other thing is most the alarm clocks I've taken apart seem to have custom displays built in, instead of the single ones that look like this:
    http://www.rohm.com/news/images/la-301bb_bl.jpg

    Does anyone know of any clocks that have the single block version of the 7 segment inside that could be hacked?

    Or does anyone know of how I could build a clock that would be designed to use the single block 7 segments?
     
  2. Skylined

    Skylined Active Member

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    It's the same, you can use single digit, two digits or any digit number 7 segment display.
    The ones that have several digits, they have a common cathode or common anode.
    They all work the same way, a common cathode or anode and then a pin to drive each segment.
     
  3. Turbokeu

    Turbokeu Member

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    I'm thinking since quite a bit of time to build a blue 7-segment clock too. :)
    I bought and used already 14 of those Digikey blue 7-segment displays (LTS-5501 and LTS-5503).

    Since most "standard" 6-digit 12-24H clock chips (MM5314,MM5315,MM5375 and other) are now obsolete, the most obvious solution is to use a µ-controller.

    I already build a 4-digit PIC16F84 based countdown timer with muliplexed 7-segment red displays, and also a PIC16F876 based clock/timer with 4x16 LCD and DCF77 receiver module, and also a digital flowmeter with blue displays.
    It would not be too difficult to merge the schematics to obtain a 6-digit blue 7-segment display clock (with or without DCF77 module) and to redevelop parts of the firmware.
    I was thinking of a cheap PIC16F648A (4KB Flash,16 I/O lines, DIP18) as the brain.

    More work to do now...:D

    CD :)
     
  4. theshadow27

    theshadow27 New Member

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    while you could poke around and change the resistor that sets the current for the whole display, i agree with turboku, a PIC would be a perfect soulution. howver, the pic does not have enugh IO lines to drive the leds directly. luckaly, there are a bunch of chips desigend especialy for driving LED arrays that work of a rs232 interface, so this wouldent be a problem.

    if you did build your own clock... you could get a seriel drive radio module and throw that in too. also dont forget snooze, alarm, etc.

    best of luck
     
  5. Turbokeu

    Turbokeu Member

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    Conrad and other stores sell those DCF77 radio modules.

    You don't need that much IO lines, I always use multiplexing for the displays.
    That makes:
    - 6 outputs for the display select (by using a 3 to 8 decoder -74HC138 or 74HC238- you can do it with 3 outputs).
    - 7 outputs to drive the 7 segments, 4 outputs if a BCD to 7-segment decoder is used.
    - 1 input for the DCF77 decoded signal. (no need for pushbuttons since the clock is synchronized with the DCF77 signal)

    Total: 8 or 14 IO-lines, not that much.

    If you need buzzer and alarm functionality, add a couple of IO's.

    PICs with up to 32 IO-lines are available (DIP40).

    CD :)
     
    Last edited: 10 Oct 2004
  6. Explicit

    Explicit New Member

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    The custom displays I was talking about are ones that don't look like the regular one, two, or three digit blocks. Instead they have AM/PM and the : inbetween the hours and minutes. So no, it's not an easy swap out.

    I also don't need snooze, alarm, radio etc. I just want a clock :)

    So, pic microcontroller eh?
     
  7. Turbokeu

    Turbokeu Member

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    When I was speaking about radio it's not common radio broadcasting (music), but the 50KW DCF 77.5KHz AM transmitter located in Mainflingen, Germany.
    This transmitter sends out a continuous serial 58bit time signal every minute (speed 1 baud!) containing hours, minutes, day of month, day of week, month, year and timezone with a precision of 1 millionth of a second (or 1 sec in 1 million year) and is usable in a range of about 1500km from the transmitter.
    Through a little module (DCF77 receiver) this signal can be decoded and used to synchronize clocks (my watch is DCF77 radio-controlled :D).

    Conrad used to carry these modules, maybe other stores do.

    Anyway, even equipped with a DCF module, a PIC based clock must have its own 24H time routines in case of absence of DCF signal (transmitter maintenance, bad reception...).

    I already developed 6-digit 24H clock routines, DCF77 synchronization routine, 4-digit LED 7-segment display routines, all that's left to do is modify the 4-digit routines to 6 digits, put all these routines together and develop the schematic.

    CD :)
     
  8. SteveyG

    SteveyG Electromodder

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    I made a clock a while back.

    They're not very difficult things to make, and when compared to my MSF clock it's only lost 4 seconds since I made it (April?), which isn't too bad...
     
  9. Explicit

    Explicit New Member

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    SteveyG I saw your clock, very nice...

    Yours would have been even more work than the one I want to make I think, all the LEDs needed to be controlled in groups I assume instead of just a 7 pin or 8 pin connection.

    So what did you use, a pic, a crystal of some sort, and a way for the info from the pic to be converted to display what you wanted?

    I think I'd rather have mine so that only the digits used show up instead of leading zeros...
     
  10. SteveyG

    SteveyG Electromodder

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    Each digit has one common cathode (or anode? - I can't remember now). All the segments are connected so that segment a of digit 1 is connected to segment a of digit 2 and of digit 3 and of digit 4 etc. and so on for all the segments. This leaves you with 6 cathodes and 7 anodes (+ colons)which are connected to the outputs of the PIC.

    You can get rid of the 0's easily in code if you wish. The only other components are buffers for the output of the PIC, which you won't need if you're using a 7 seg display (I only needed them because I was driving all those LED's) and a 4MHz crystal and buttons (+resistors and caps etc.)
     
  11. dfhaii

    dfhaii internets

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    Maplins in the UK sell msf antenna and decoders(about £20 all in), I have been planning a 'msf pic 7 segment clock' type affair for a while now.

    There is plenty of code available on the net for using the msf data or you could write your own as its very well documented.

    Good luck.
    Col.
     
  12. MrBadidea

    MrBadidea New Member

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    Or you can be just super-geeky and make a BINARY clock ;)

    I'll have to dig mine out, did it last year as my project for A-Level electronics... I pity the fools who made 10 second timers :rolleyes:
     
  13. Explicit

    Explicit New Member

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    Explain to me how I would make a binary clock with 7-segment LEDs? Actually don't.

    Isn't there any IC's designed for this task? What would Sony use in one of their alarm clocks?
     
  14. MrBadidea

    MrBadidea New Member

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    You don't.

    You use 4 LEDs per digit, in binary fasion, using BCD numbers. There is a chip designed for this... I just can't remeber what it was...

    I know that there are other chips you can stick on the output of that chip that would allow you to drive a 7-segment display, or there are other chips again that can do both jobs in one IC.

    The concept of my binary clock was amazingly simple but I just don't have the time to write it up atm.
     
  15. Explicit

    Explicit New Member

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  16. Explicit

    Explicit New Member

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    Anyone?
     
  17. Turbokeu

    Turbokeu Member

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    Found another integrated clock chip: the NTE2060/2061
    Available here.
    This one has alarm and snooze integrated too.
    Unfortunately I couldn't find any application note. :miffed:

    The older National Semiconductor chips (MM5414, MM5375) seem very difficult to source.

    Back in 1973 I made four 6-digit digital clocks with red LED 7-segment displays based on the MM5314N.
    One is still running (since more than 30 years!) at my parents house... (equipped that one later with 20mm displays instead of the original 8mm displays).
    At that time I paid about £15 for a MM5314N, and about £7-8 per (8mm) red 7-segment display from Opcoa...

    Anyway, actually busy drawing a schematic based on a PIC16F648 microcontroller, with 74HC138 or 74HC238 decoder followed by six BC337 driver transistors for addressing the muliplexed displays, 4543 BCD to 7-segment decoder and UDN2981 (or TD62783A) high-side driver to drive the Common Cathode segments (the 4543 can supply only 10mA peak per segment and as the displays are multiplexed (16.6% duty cycle for 6 digits) you need at least a current of about 40-50mA/segment for the blue Digikey displays to obtain a suitable brightness).

    Since the PIC routines are very time-critical to obtain a suitable long time precision I still prefer to use a DCF77 receiver-decoder module to synchronize those routines.

    This DCF module is available from Conrad Netherlands (search for part 641138), and priced at 9.95 Euro (about £6.86).

    Will post back as soon I have the schematic in electronic form.

    CD :)
     
  18. Explicit

    Explicit New Member

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    Oooh, the NTE2060 & NTE206 look very sweet, they can even drive LEDs directly.

    I'd like to just use a single chip if possible, because I don't know anything about microcontrollers, and programming them.

    I think this one runs off of a rectified mains line, and thats how it uses 60Hz as a reference, I read thats how the cheaper less accurate clocks work, and the more accurate ones run crystals or oscillators?
     
  19. Turbokeu

    Turbokeu Member

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    Yeah, the 4543 driver can drive LEDs directly too but is limited to 10mA peak per segment (so do most of those one-chip clocks) and therefore need low current/high intensity LED displays (5-10 mA per segment) to work properly.

    Unfortunately blue displays are nor low current, nor high intensity...
    Even with a one-chip clock you will need to use a ULN2003 low-side driver or a UDN2981 high-side driver, depending on the displays (CA or CC).

    CD :)
     
  20. TheAnimus

    TheAnimus Banned

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    The one i just opened up, a custom chip, prolly a PLD.

    but as people have said, there are BCD drivers etc about, but most clock parts (RTC's etc) are designed for micro based designs where reducing PCB tracks is paramount.
     

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