LED based clock project

Discussion in 'The Projects Forum' started by Robert Walpole, Apr 25, 2010.

  1. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    Hi,
    I am working on a clock project at the moment and I need a little help with the circuits.

    It is to be built inside a Haywards pickled onion jar with an internal diameter of 3 3/4 inches and a height of 4 1/2 inches, there is a picture of the jar in question attached here.

    The clock is based on 168 LEDs.

    1. 1 LED for each second in a minute. Total of 60
    2. 1 LED for each minute in the hour. Total of 60
    3. 48 LEDs, two for each hour, split onto an upper and a lower level
    The second LEDs are red, the minutes are blue and the hours are green.

    These LEDs are split up into 12 panels, which will be pressed against the inside of the jar. I have included an image of the proposed layout, the numbers represent the sequence in which the LEDs should turn on. The black lines divide up the panels. Imagine the strip as if it wer glued on the outside of the jar and in proportion.

    I have a circuit that I designed in circuit wizard to count the seconds and keep the LEDs lit (so all 60 second leds would be lit at the turn of the minute, all 60 minute LEDs at the turn of the hour and all of the LEDs in the clock at 23:59:59). An identical circuit, taking its output from the end of the seconds circuit can be used for the minutes. I have included a copy of the Circuitwizard file for those who are interested. There are also three pictures of the circuit here, here and here

    There are a number of issues with this circuit though:

    1. It takes its timing form a 555 timer, if the 555 timer is off by a fraction of a second, the clock could be a few minutes off by the end of the day.
    2. I can’t work out how to make it reset, so once the LEDs are lit, they stay lit forever (or until the battery goes). Also, this makes it impossible to carry the seconds over to the minute side
    3. None of that matters anyway because the circuit boards required would be massive and there is now way that they would fit in a pickle jar. Even after modularising the circuit I cant get a single one to fit in the jar, never mind the 24 modules that would be required, plus the LEDs, 555 timer, battery and the inductive charger I was planning to put in the base.
    So, I am completely stumped. I really want to make this project work but I have reached the limit of my circuit design skills.

    Is there any chance you guys could help me out?
     
    Last edited: Apr 25, 2010
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    Well, well, well.

    Shrinking the circuit will be the easi(er) part. Getting it to work is the hard part.

    Using SMD leds and a flexible PCB, you could design it flat, then roll it and put it in the jar.
    That will take care of the "display"

    The timing is a little tougher. You can use an AND gate connected to the 60th and 1st second leds to give you a high when the 60 second mark is hit and going to the 1st second. That can be your reset pulse to reset the seconds led counter. The AND will also pulse a counter to add 1 to the minute counter.

    The minute counter will be EXACTLY the same. It will advance count from the seconds counter AND gate.

    The hours will advance from the and gate from the 60th and 1st minute AND gate.

    The hours counter will use an AND gate on the 24th and 1st hour to reset the whole kit and caboodle.
     
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  3. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    The circuit I have would work fine with the and gate layout you proposed.

    The size is the main issue though, im using a series if 4017 chips in a cascade at the moment. Is there a more compact method, perhaps using a different chip?
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    The AND gate should solve you problem.. just a simple add to your existing circuit.

    As for the 4017, you can get smaller 4017..like smd type packages, instead of PDIP.

    That will shrink the size. Also think of using multiple stacked boards for the processing part for the display.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Are you using scr's in series with the leds?

    When the leds are on one by one you could think of multiplexing.

    Bertus
     
  6. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    Youve lost me there.

    The SCRs are in series with the LEDs.

    I know what multiplexing is, but I would have no idea how to implement it.

    As for using a smaller 4017, circuit wizard a fairly basic design package. Could you reccomend a better (preferably free) one with a simulation feature.
     
  7. retched

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  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you use scr's in series with the leds, the leds will stay on and multiplexing is not possible.
    The leds will not go off until the power is disconnected.

    I also do not see current limiting resistors at the leds.

    Bertus
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    Yes, I dont see a need for the SCRs. Was this just to keep the LEDs lit?
     
  10. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    Yep, the SCRs are to keep the LEDs lit.

    Will a resisto be necessary. I was just going to use LEDs with a higl voltage tolerance. Not having them would save on parts.

    edit

    I see what youre getting at, resistors will be necessary. More parts though.
     
  11. retched

    AAC Fanatic!

    Dec 5, 2009
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    Well, you might just burn them up. You need the resistor.

    You may try to get LEDs with built in resistors.
    You can also use REALLY small SMD resistors directly on the anode leg of the led.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I have a binary coded decimal clock, only requiring about 21 LED's & now its location is lost to me, used for about a month. Dificult to read in the dark as frame of reference is lost without adding more different colored LEDs to mark collumns & levels. Your project is interesting, labor & $ intesive & may fall out of favor in relative short time.
    Are the SCRs something like 2N5060's? To reset , may need to interupt power to LEDs when logic is reset via FET switch.
    There is a recent discussion on AAC on clock time bases using quartz clock parts & 4060 IC. Battery drain is going to be cansiderable with 160 LEDs on all at once-part time.
     
  13. retched

    AAC Fanatic!

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    Battery drain and it will be awful HOT in that jar at 23:59:59. With all those LEDs lit..

    I cant believe it didnt cross my mind earilier.
     
  14. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    Battery drain shouldnt be a problem, it will be kept in a cradle with an induction charger powering it for 99.9% of the time. I only want a battery backup so I can pick it up and pass it around. The total power drain at 23:59:59 is 11-13 watts so I figured it would be near impossible to run it of a few AA batteries at the beginning.

    As for the heat, I dont think it should be too much of a problem LEDs put out next to no heat. Even is it is, I can just fill the jar with mineral oil to average out the heat over the 24 hour cycle.

    I have made a bit more progress on the circuitboards:

    1. The second count carries over to the minutes and the minutes to the hours and the whole kit resets at 24:00. I did this using reed relays that are tripped by the 5th pin of the 12th timer for the minutes and seconds, with the output from the pin being amplified by a transistor and the current to the anode leg of the thyristors being managed by a reed relay.
    2. I have designed a board that takes the thyristors, LEDs and resistors which frees up a lot of space. I dont think space will be an issue any more (Pictures of circuitboard here)
    Im running a sim of the circuit at the moment (picture). I am at 1hr 11min and 59 sec. Dont worry about the missing LEDs at the beginning of the second count. Thats only because I have set the pulse timing for the 555 to about 1/10 of a second so the beginning of the count tends to get cut off by the relay. It isnt a problem in a real time sim.

    Thanks
    -Robert
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
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    How are you SETTING the time?

    I guess the easy way would be to wait till 23:59:59 to turn it on. ;)
     
  16. Robert Walpole

    Thread Starter New Member

    Apr 25, 2010
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    There are two push to make switches (pictured here) that connect to the minute timing rail and the hour timing rail to the positive terminal on the battery. When one of the switches is pushed, it pings the 4017 cascade, advancing it one minute or one hour, depending on which switch you push.

    Oh, and I got my power calculations wrong. Peak drain is under 10w.
     
    Last edited: Apr 28, 2010
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