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Electronics 7-segment LED Clock

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

  1. Turbokeu

    Turbokeu Member

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    Weird, I got 49 mails in my skynet mailbox this morning... :confused:

    The exact syntax is:
    turbokeu at skynet dot be or chris dot deceuninck at skynet dot be

    Or you can also use:
    turbokeu at turbokeu dot com

    CD :)
     
  2. tomjediknightt

    tomjediknightt New Member

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    ummm, Hi chris,
    I was using turbokeu@turbokeu.com and it isnt going to you. i keep getting it back.
    Yep, just doublechecked. thats what I have down for you. No matter glad to still chat here on bit-tech forum.
    I got my PIC book the other day. They are using the 16F84 as a sample chip to use.
    Now b4 I can go on, I have to get the PICbasic complier and programmer.
    And I am fresh out of money :(
    -tom
     
  3. tomjediknightt

    tomjediknightt New Member

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    Hi StevyG,
    I really liek your 1" clock there. Using a pic micro? I just got some 1" green from digi-key. Can you share schematic and/or program? if not, plan on selling a kit?
    can you make it switchable between 12 and 24 hr display?
    thanks
    -tom
     
  4. star_treking

    star_treking New Member

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    Anyone know of any led alarm clocks that have seconds on it.

    All I can find that has seconds is something in the $200 dollar range. There are plenty of cheap lcd clocks with seconds but I wouldn't know where to begin to mod it to accept custom led display.

    Velleman has exactly what I want except its still too expensive for me.

    Am I blind or are there no cheap led clocks with seconds?
     
  5. kazawolf

    kazawolf New Member

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    non-multiplexed 7-segment clock chip

    Hi,

    I was wondering if anyone knew of a non-multiplexed 7-segment display clock chip. I am building a clock with unusual output and just need raw data that doesn't have to be decoded.
     
  6. SteveyG

    SteveyG Electromodder

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    Tom: I could draw up a schematic for you, but I'm not living at home at the moment (where my computer is) so I can't give you any code. I'll try to draw something up when I get a spare moment at work today. The 12hr/24hr thing is easy to setup in code.

    kazawolf: You won't find any devices that directly drive all the segments of a display. You could either use a standard clock chip with a series of data latches to drive them directly, or create your own circuit.
     
  7. SteveyG

    SteveyG Electromodder

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    The schematic is a bit brief, but you get the idea:

    [​IMG]

    The displays are digit-at-a-time multiplexed, so you may want to beef up the NPN transistors if you drive the LEDs near their peak pulsed forward current. I used the ULN2003 on my clock so that wasn't an issue.

    Secs/Mins/Hours were on external interrupts, and pull ups enabled on port b. I think I had other buttons for brightness, alarm etc on PortB too leaving PortB<6:7> for ICSP.

    If you have bigger displays with more than two LEDs in series per segment, you'll want to run the displays from a higher voltage than 5V, so add pull-up resistors to the base of the PNP's and change the multiplexing strategy so that only the pins driving the active segments are pulled low and the others are high impedance (not high!).

    Hope that helps.
     
  8. kazawolf

    kazawolf New Member

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    SteveyG,

    Thanks for the advice using D latches...hadn't thought of that but it makes perfect sense. I'm sure I will be back with more queries!

    Roger
     
  9. foxx

    foxx New Member

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    Well, I have noticed this thread before, and clocks have always amazed me. So this weekend I decided to start learning about them. I havnt read every detail to this thread, but Ive skimmed every page. So if a question of mine is already answered, please direct me to the page that it was asked, thank you.

    As for my clock that I am hopefuly going to build...well, pictures are worth 1000 words.

    (Here is the metafile.)
    [​IMG]

    If you see ANYTHING wrong with my circuit diagram (Im not exactly an electronics guru), or if you see anything that could be made simpler (less chips!), please point it out to me.

    If you are confused over some of it, see if this clears it up. If not, feel free to ask me about it.

    (Here is the parts list)
    Code:
    Bill of Materials for:
    6 digit clock.BOM
    
    Item	Label-Value	Attributes	Designation
    1	1uF		POLAR0.6	C1
    2	.01uF		RAD0.2		C2
    3	LED1		DIP2		D1
    4	LED1		DIP2		D2
    5	LED1		DIP2		D3
    6	LED1		DIP2		D4
    7	1N4934		DIODE0.4	D5
    8	1N4934		DIODE0.4	D6
    9	1N4934		DIODE0.4	D7
    10	1N4934		DIODE0.4	D8
    11	1N4934		DIODE0.4	D9
    12	1N4934		DIODE0.4	D10
    13	REDCC		(none)		DISP1
    14	REDCC		(none)		DISP2
    15	REDCC		(none)		DISP3
    16	REDCC		(none)		DISP4
    17	REDCC		(none)		DISP5
    18	REDCC		(none)		DISP6
    19	716.42k		AXIAL0.4	R1
    20	7.16k		AXIAL0.4	R2
    21	48.33		AXIAL0.4	R9
    22	48.33		AXIAL0.4	R10
    23	48.33		AXIAL0.4	R11
    24	48.33		AXIAL0.4	R12
    25	48.33		AXIAL0.4	R13
    26	48.33		AXIAL0.4	R14
    27	72.5		AXIAL0.4	R15
    28	72.5		AXIAL0.4	R16
    29			DIP2		S1
    30			DIP2		S2
    31			DIP2		S3
    32	74LS90		DIP14		U1
    33	74LS248		DIP16		U2
    34	74LS248		DIP16		U3
    35	74LS90		DIP14		U4
    36	74LS90		DIP14		U5
    37	74LS90		DIP14		U6
    38	74LS248		DIP16		U7
    39	74LS248		DIP16		U8
    40	74LS90		DIP14		U9
    41	74LS248		DIP16		U10
    42	74LS90		DIP14		U11
    43	74LS248		DIP16		U12
    44	7408		DIP14		U13
    45	555		DIP8		U14
    46	7402		DIP14		U15
    46	7402		DIP14		U15
    
    If you are wondering why I am using a 555 its because I have no idea how oscillators/crystals work and I dont know how to use them properly (cookie to anyone who will replace the 555 in my circuit with a 1hz crystal :D ).

    If you are wondeing why I am using TTL instead of a PIC its because I have tried to learn assembly before and I just dont like it. Also I like TTL more than programing (its just so fascinating to me :p ) and if I wanted to program it, I would just use my Basic Stamp.

    Finaly if you want some more spiffy stuff.
    (Color/slightly smaller.)
    [​IMG]

    (Half way through simulation.)
    [​IMG]

    (download to the circuitmaker .ckt)
    http://www.sendspace.com/file/ip1lgc

    Questions? Comments? Concernes? Ideas? Etc?
     
  10. Xiachunyi

    Xiachunyi New Member

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    For your 555 IC timer replacement, you can purchase one of those TTL output Crystal Oscillators - TTL compatible output and just divide the frequency down to 1 Hz.

    What exactly are the diodes for in the schematic diagram?

    You also seem to be relying on the pull-up capability of the LS family for input, you should go ahead and indicate that in your schematic or go ahead and add in a 1K ohm pull-up resistor.
     
  11. foxx

    foxx New Member

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    Thank you for helping,but...

    The slowest (I guess thats the right term) oscillator I can find is 1mhz. If Im getting this right, thats 1 million more than I need, right? In order to get it down to the 1hz I need I would need at least 6 decade counters. Silly me, forgot to tell you I acctualy do have a space/money constraint and I just dont have room/money compared to having a single 555. Unless, do they make centacade/millacade (SP?) counters?

    The diodes are there to prevent the 1hz signal from messing up the previous digits (if you look at the minutes and the seconds) the minutes get there frequency from the seconds. And in order to set the clock, you send the seconds frequency through the minutes, but without a diode it will screw up the digits in the seconds. (Wow, that sounds complicated, please tell me if im making no sence :hehe: ) Granted, the diode isnt really needed, its a nice touch...unless Im missinterpreting how diodes work with frequencies,in which case please tell me if they would acctualy do more harm than good.

    Now this is going to make me sound like a complete newb, but where would I add the pullup resistor? And to for future refrence/further my technical knowledge (this is just a learning experience for me), please tell me why, and how it would affect my circuit?

    Thanks.
    :)
     
  12. SteveyG

    SteveyG Electromodder

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    You'd want to divide down from a 32.768kHz crystal. You can do this with only a couple of binary counters to get your 1Hz output. (2{param} = 32768 remember)...
     
  13. Xiachunyi

    Xiachunyi New Member

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    If space/cost is the limiting factor, then I guess you can't get any better than the 555 IC timer.

    As for the diodes, if I understand correctly, you seem to use them to prevent feed-back into the outputs of the previous ICs when setting the clock with the second's signal.

    In this case, usually you will use a method called lockout and injection. The following below is a generic every-day 2x1 MUX that is capable of handling that for you.

    If you wish to set the clock, it will lockout the signal from the chips before and only feed-in the second's. If you wish for the clock to run normally, it will lockout the second's and feed in the required signal from the previous counter(s).
    [​IMG]

    You are by no means incorrect about utilizing the diodes to prevent feed-back into the previous counter chips since it obviously does work. It just seems kind of weird for a digital circuit to use diodes to transmit through to me.

    Now that I understand about your use of the diodes, you don't need the pull-up resistors. Sorry.

    Good work.
     
  14. diwee

    diwee New Member

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    -
     
    Last edited: 28 Dec 2010
  15. foxx

    foxx New Member

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    Thank you Xiachunyi and SteveyG.

    Ive revised my circuit just a bit.
    1.Ive removed the diodes and placed in a couple of 2x1 MUX's.
    2.Ive removed the double AND gate a placed in 3 individual AND gates.
    3.Cleaned up the area around the AND gates.

    Updated circuit (if you want it in other states/formats just ask).
    [​IMG]
    (BTW, I only have one resistor for all the displays because my circuit design software only allows 50 parts, in reality there will be a resistor for every led in each display)

    What is worrying me is the hour digits. As you can see, I have gotten it to reset from 12 to 0 with the three AND gates. And I have tried to add a 1 using a quadruple OR gate (where as in reality this will be 6 OR gates strung together). I can run a simulation where it will count to 12 and reset but it wont add a 1. In theory it should, shouldnt it?

    Its also the same with the clock signal.The simulation (in anolog mode) wont generate a signal (it just outputs random voltages) but in reality (based on my math) it should generate a 1hz signal correct?

    And I have no way of testing in real life to see if the 555 is outputting the right KIND of signal for the 7490. (Ive never used any kind of timing before in previous circuits so I dont know if there is even different kinds. :duh: )

    Finaly, do you see any other possible problems with my circuit?

    :)
     
  16. Xiachunyi

    Xiachunyi New Member

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    To reset from 12 to 1, you will either have to throw away the set modulo-10 74xx90 counter for the hour portion and build your own from scratch, or try isolating it and injecting a another pulse right after it resets.

    The reason the solution does not work, tell me if I've misunderstood, is that you are applying the reset to the ripple carry-in input with the clock. This does not work since it violates the set-up and hold times for the Flip flops in the 74xx90 because it is in master-slave format.

    For setup and hold, you will need to apply your signal before the rising edge of the clock and hold it there a little after the falling edge.

    In order to combat this, you will need to, after your reset signal has been issued, take the signal and hold it out longer for the ripple-in. To do this, you can probably use a 555 IC timer wired in one-shot mode to give you an output pulse length that is long enough to justify the input for the next clock rise and fall duration. You may need to actually bread-board this portion since it will give you the "working" values.

    ---
    For the 555 IC timer, you will need to either add a pull-up or pull-down resistor since its output is either open-collector or open-emitter respectively. Place the pull resistor, probably 1K ohm, on the 555 IC timer's output pin.

    The reason for the addition is because, say the output of the of the 555 IC timer is open-emitter, that means the chip will pulse out a positive voltage and then just float the pin (it will not pull it to ground). For the 'LS' family, since the pin is left floating, it will automatically be pulled up by the internal pull-up resistor. This means your input will never be a '0' (For active-high logic), it will always be a '1' under perfect circumstances. It may be a '0', but that is because of something like interference like static electricity.

    ---
    As for problems, since you are using a push-button, say S4 on your schematic, you are leaving the input of the logic gate to float (disconnected) whenever there is nothing pressing down. Since the 'LS' family pulls up internally, that may not be a problem but make sure to make a note of it since another person utilizing another TTL logic family will get in trouble.

    I would suggest for push-buttons, a debouncing circuit, but if it works -- it works.

    ---
    To diwee

    Do you have to multiplex the tubes for any reason besides utilizing less wires and driver chips? What are the specs of the tubes themselves?
     
  17. kazawolf

    kazawolf New Member

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    Another question re non-multiplexed chip

    Hi SteveyG and fellow uhrmeisters,

    I did manage to find a direct-drive clock chip (NTE2060, possibly hard to obtain) and had another rudimentary question, since I know very little about electronics. Let's say the time output is 12:34. How would one "sequence" that data, so that for example, the "1" appears for two seconds, followed by the "2", then "3", then the "4." I'm sure there is a simple CMOS type chip with this exact application, I just can't think of it offhand.

    I do appreciate your help!

    Roger K
     
  18. SteveyG

    SteveyG Electromodder

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    Is the idea to display the whole time on a single digit? You'd probably want a 4:1 multiplexer, but you'd need one for every segment of the display. (so 7)

    A 4:1 multiplexer has 4 inputs, one output and 2 'select' lines. select <= 00 would pass input 1 to the output, select <= 01 would pass input 2 to the output, select <= 10 would select input 3 and select <= 11 would select input four. The select lines could then all be connected in parallel to a 2 bit binary counter to scroll through as you describe.
     
  19. foxx

    foxx New Member

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    I think we are a bit lost in translation when it comes to the adding 1 (it is pritty confusing followin the diagram in the lower left corner). What I have is a bunch of OR gates set to go high on CP1 when the see the displayes are showing 00. which should add 01 to the displays and the OR gates will stay high (right?), and then it gets to 1:59 which is making both CP0 and CP1 high, and then the 'minutes' reset, sending CP0 low making the display show a horozontaly flipped 6 (2+1) but since there is the OR gate it sees the 02 is there and sends CP1 low. And the 7490 continues along untill it resets back from 12 to 0 where it does it all over again. Right?

    Or will the OR gates not let CP1 go back high unless it sees the 00? In which I have the diode (just a random one I picked out) there to prevent it from doing so.

    --

    I have been looking at the mA output of the 7448 and the mA draw of the displays. Well from the data sheets Ive seen, the 7448 can only source about 2mA and my displayes take 60mA. No problem, Ill just use some 7447's with some CA displays, wrong. The 7447 can only sink 18mA. So as a last resort, Ill have to solder 47 transistors (its going to be a tight fit, but I think I have an idea). I was looking at the 2n2222 for a transistor, unless you have a better suggestion.

    --

    As for those switches, I have removed S4 therefore I wont need a debouncer. On S3 and S2 I SHOULD have one, but I think it wont really matter that much.

    --

    On my 555 ,which is giving me the 1hz output, I put a 1k ohm pull-up resistor.

    --

    Other problem spots you see?

    --

    Here is the current state of my circuit, Ive dubbed it version 2.1 (first post I did was version 1, the second post of mine was version 2)
    [​IMG]

    (And yes, I must insist on saying this each time I post :D )
    Thanks.
     
  20. Xiachunyi

    Xiachunyi New Member

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    I can see what you are doing and looks like it will work the way you described. As for the diode, try ORing the output of the multi-input NOR gate with Q0 and feeding it into CP1 since you are creating a short by feeding the output of the NOR to the output of Q0 whenever the counter is at 0000.

    As for the sinking current, the 74xx47 BCD to decimal decoder can handle it if you size your resistors to limit the current in order to avoid soldering on transistors.

    I do not know if you have addressed it before, but your 8-input NOR gate looks weird with 1 input left open and 3 inputs tied to ground.
     

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