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555 Timer Circuit and 4017 Decade Counter

Discussion in 'General Electronics Discussion' started by Derftoy, Nov 6, 2012.

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  1. Derftoy

    Derftoy

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    May 9, 2012
    I am currently messing around with this circuit:

    http://www.555-timer-circuits.com/knight-rider.html

    It is running on a 9v Battery, and I have found that running on 9v, doesn't last very long. So I am trying to run this through 6 volts (Battery Holder with 4 AA batteries).

    If I connect an LED directly from the 555 output, it flashes and is very bright. But once, I connect the output of the 555 to the clock input of the 4017 chip, the lights work as planned, but they are much dimmer. In the explanation, it says that the LED's are running at 7mA, and I would like to get that up around 15mA, so my super bright LED's will glow!

    So, why is the LED so dim running off the 4017?
     
  2. CocaCola

    CocaCola

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    Apr 7, 2012
    And you will send it to an early grave doing that...

    Because there are current limiting resistors like there should be, you need to lower the value of those resistors to increase the current...

    Go read Steve's LED tutorial...

    https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html

    FYI, the 4017 maxes out at 15mA so don't try to milk more out of it or risk wrecking it... If you want more current you will need to use transistors or a Darlington IC...
     
    Last edited: Nov 6, 2012
  3. Derftoy

    Derftoy

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    May 9, 2012
    When I connect an LED directly to the output of the 555, I am of course using a 330 ohm resister. It is much brighter than what is coming out of the 4017 which is connected to 100 and 200 ohm resisters.

    I can't seem to figure out what the voltage should be out of the 555 output from 6volts. From what I have read, it should be 4.3 volts, as it drops the voltage by 1.7. So, if I am coming into the 4017 with 4.3 volts, and that is triggering the clock, right? So, is my 4017 being powered by the Vdd (pin 16), since that is connected directly to my 6v power source, it should be getting 6v. But when I test with a multimeter, across an LED, it reads about 2.5 volts. I would be expecting to get higher voltage and current.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It's because the impedance of a 4017 output is MUCH higher than the output impedance of a 555.

    A 4017 (see CocaCola's response above) is capable of about 15mA; the 555, around 200 mA.

    Think of it as an extra resistor in series with the LED. For the 555 it may be about 30 ohms; for the 4017, about 400 ohms.
     
  5. CocaCola

    CocaCola

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    Apr 7, 2012
    ***Edit*** in addition to what Steve said...

    That 4017 circuit is a 'flawed' design, IMO...

    Look for example at LED #4, when pin 8 of the 4017 is 'high' to light the diode, pin 2 of the 4017 is 'low' this creates a voltage divider between pins 2 & 8 giving you 3 volts to the LED...

    At least I'm pretty sure the 4017 sinks while the pin is low...
     
    Last edited: Nov 7, 2012
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
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    Jan 21, 2010
    Very true. You really should have diodes there. In fact you could replace the resistors with diodes, and at a low voltage (say 6V) the 4017 will not suffer.
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    The link he provided basically confirms that.

    Chris
     
  8. CocaCola

    CocaCola

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    Apr 7, 2012
    You know, I skimmed over that sentence and failed to actually 'read' it :) I'm perplexed why it was designed like that...
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    I don't know either. Maybe we have to be fans of Kit the car to know. :)

    Chris
     
  10. CocaCola

    CocaCola

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    Apr 7, 2012
    As someone who has designed a KITT circuit that was focused on accuracy the term "KITT circuit" has been abused, the real one in the TV series has lots of trailing light (in fact the 'off' time of any given light in the circuit is minimal to nil, as soon as it fades out fully it's lit again on the return sweep) very few of the online circuits mimic this... :cool:

     
  11. wingnut

    wingnut

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    Aug 9, 2012
    I happened to have the same circuit lying around with 555 and 4017 both running off the same 6V battery. The brightness of my red diodes looks fine. Only one LED is glowing at a time and I am using 120 to 150 ohm resistors on each LED.

    Maybe a wall-wart, plug in external power supply could help.
    Old desktop computers have lovely 5V power supplies too, and one can wire them to get 6-7 or 11 volts too.

    You could use an ULN2003A or ULN2803A chip which is an array of 8 Darlington pair transistors to amplify the current to your LED's. They push out 300mA. And these are cheaper than the postage.

    I too like to play with circuits - and having gone to the trouble of making one, I tend to keep it assembled, pasting the breadboard to the circuit diagram. I know that I will want the circuit again in future (such as when someone like you asks about it :) )
     

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    Last edited: Nov 7, 2012
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    I agree with CocaCola. The claim that this 4017-based circuit gives a "very realistic effect" is rubbish IMO. I clearly remember the KITT display and there's no way a 4017 with a regular clock will produce an accurate simulation.

    I think there are some microcontroller-based designs available on the net and I would recommend one of those instead of this very poor design.
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I know next to nothing about knight rider. It wasn't on my must see list. Maybe if Babe Watch had a grill like that I would have paid attention. :D

    Chris
     
  14. Derftoy

    Derftoy

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    May 9, 2012
    I thank you for the many thoughts on this project. I have been toying around with putting transistors into the circuit and running the LED's off the 6v directly and using the counter to only activate the LED's.

    I thought of the diode approach as well, but I know next to nothing about diodes and how to get the right size or what I would need. I need to do more research on this.

    Thanks for the info.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    You can use any of the 1N400x series diodes. The 1N4001 and 1N4002 are extremely common and dirt (pennies) cheap. The Anodes should be connected to the 4017. Just make sure you heed to what Steve said.

    Chris
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I usually run my browser with add-ons disabled, so I didn't watch this video when you posted it. Well, I watched it and yes, it's close to what I remember. While I was at youtube I also viewed this one. It must be uC based because it does everything but the tango! For sure, most of what it can do will land you in jail for impersonating a police officer.



    Chris
     
  17. CocaCola

    CocaCola

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    Apr 7, 2012
    I still don't see the trailing lights in that one... But just the same as you said unless it's a show car these lights are highly illegal in most areas...

    In the original car the sweep was done with bulbs, a lot of the trailing is just the effect of the the bulb itself not going instantly black like LEDs do... So to do this 'correctly' with LEDs you really need to use PWM and create a percentage trail behind the currently fully lit bulbs...
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    There were many effects there. I could swear that I saw that effect in his repertoire.

    On the other hand, your powers of observation have proved to be quite acute! ;) Besides, I'm overdue with my visit to my optometrist. Look at my avatar. That glassy look was from over a week of being without my glasses at my sister's home in PA.

    WARNING: Do not hand your wife your glasses while driving and ask her to clean them! Ever!!

    Chris
     
  19. BobK

    BobK

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    Jan 5, 2010
    I see a trailing effect, it just doesn't go across the entire range, it trails off for about 5lights behind the moving section.


    Bob
     
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