+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Newbie level 3
    Points: 27, Level: 1

    Join Date
    Jul 2015
    Posts
    4
    Helped
    0 / 0
    Points
    27
    Level
    1

    Chasing LED Circuit Design Issues

    Hey Guys, I have a few question relating to my chasing led circuit but before i get into that I'll explain a bit. The aim of this circuit is to have 10 LED go on and off right after each other giving of the illusion that the LEDs are chasing each other.

    MY QUESTIONS
    1) Looking at my design would any component values need to be changed?
    2) Do resistors lower the current or just the voltage?
    3) How can I modify this circuit to make all the LEDs light up at the same time and stay that way as well as the chasing LED option?

    Cheers in advance :)

    Last edited by BradtheRad; 19th July 2015 at 04:25. Reason: Image converted from external server to Edaboard attachment

  2. #2
    Junior Member level 1
    Points: 871, Level: 6

    Join Date
    Jun 2014
    Posts
    18
    Helped
    1 / 1
    Points
    871
    Level
    6

    re: Chasing LED Circuit Design Issues

    Quote Originally Posted by Peter Knott View Post
    Hey Guys, I have a few question relating to my chasing led circuit but before i get into that I'll explain a bit. The aim of this circuit is to have 10 LED go on and off right after each other giving of the illusion that the LEDs are chasing each other.

    MY QUESTIONS
    1) Looking at my design would any component values need to be changed?
    2) Do resistors lower the current or just the voltage?
    3) How can I modify this circuit to make all the LEDs light up at the same time and stay that way as well as the chasing LED option?

    Cheers in advance :)

    LINK TO PCB SCREEN SHOT http://gyazo.com/4b756caa4304a4bda342044cb1a86b11
    Can't tell without a schematic showing your circuit..



    •   AltAdvertisment

        
       

  3. #3
    Newbie level 3
    Points: 27, Level: 1

    Join Date
    Jul 2015
    Posts
    4
    Helped
    0 / 0
    Points
    27
    Level
    1

    Re: Chasing LED Circuit Design Issues

    Oh okay, here you go

    Last edited by FvM; 19th July 2015 at 08:47. Reason: Image uploaded to Edaboard



  4. #4
    Super Moderator
    Points: 76,741, Level: 67
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    12,548
    Helped
    4183 / 4183
    Points
    76,741
    Level
    67

    Re: Chasing LED Circuit Design Issues

    There is no method to make all the 4017 output go high at the same time so you need to provide another path for the LED current to flow through. The simplest is another diode (1N4148 for example) to each of the transistor collectors. The anode of the diodes go to the collectors and all the cathodes are joined together. In normal 'chase' mode you leave the cathode junctions floating, for 'all on' you connect it to 0V.

    There is a potential problem in your schematic. It works at the moment because R1 only has to carry the current for one LED at a time but when you turn all 7 on at the same time it will reduce the LED current significantly and you might find they are all dim. The only solution is to short out R1 and wire an individual 330 Ohm resistor in series with the anode end of ech of the LEDs. That way their brightness stays the same whether chasing or continuously on.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



    •   AltAdvertisment

        
       

  5. #5
    Newbie level 3
    Points: 27, Level: 1

    Join Date
    Jul 2015
    Posts
    4
    Helped
    0 / 0
    Points
    27
    Level
    1

    Re: Chasing LED Circuit Design Issues

    Oh, I see what you are saying but how would you connect them all up without disturbing the pulses coming out of the 4017B IC?

    In the first paragraph you stated a method using diodes and stuff. Could you give me a visual demonstration of how that would be done Thanks
    Last edited by FvM; 19th July 2015 at 09:59. Reason: Posts merged



  6. #6
    Member level 4
    Points: 1,380, Level: 8

    Join Date
    Dec 2010
    Location
    London
    Posts
    72
    Helped
    14 / 14
    Points
    1,380
    Level
    8

    Re: Chasing LED Circuit Design Issues

    Im wondering if you need the transistor to light every led? Would guess wiring them directly to the 4017 would suffice, speacially if they are high brightness types that only require 5mA or so. Similarly, inverting the polarity of the leds should light all but the one 'chasing' effectivelly inverting the circuit (that is negative to the 4017 output and positive to VCC with a series resistor). Just a guess tough, havent worked with 4017 for some long time.



  7. #7
    Newbie level 3
    Points: 27, Level: 1

    Join Date
    Jul 2015
    Posts
    4
    Helped
    0 / 0
    Points
    27
    Level
    1

    Re: Chasing LED Circuit Design Issues

    Oh just fixed it... It now has two switchs, first one is to power (On Off), Second one is to change from chasing LEDs to all LEDs lit up. I used diodes which connected from the anode side of the LED and between the Collector side of the transistor (On every LED and transistor) Then I just rearrange it so the end of the diode would go to earth.. :) Hope you get what I mean Haha Thanks everyone for the ideas resulting in a positive conclusion. Cheers :)



  8. #8
    Advanced Member level 5
    Points: 49,577, Level: 54
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,628
    Helped
    2010 / 2010
    Points
    49,577
    Level
    54

    Re: Chasing LED Circuit Design Issues

    The base-emitter junctions of the transistors are shorting the outputs of the CD4017. Without the transistors the CD4017 can drive the LEDs directly. The datasheet from Texas Instruments shows a typical current of about 15mA into an LED when the supply is 9.0V and drops to about 5mA when the battery has dropped to 6V.



    •   AltAdvertisment

        
       

  9. #9
    Advanced Member level 5
    Points: 34,760, Level: 45
    Achievements:
    7 years registered Created Blog entry Created Album pictures
    SunnySkyguy's Avatar
    Join Date
    Sep 2007
    Location
    Richmond Hill, ON, Canada
    Posts
    6,698
    Helped
    1671 / 1671
    Points
    34,760
    Level
    45
    Blog Entries
    7

    Re: Chasing LED Circuit Design Issues

    Falstad java Sim


    Showing 2 drivers & LEDS out of 9 or anything <=10 determined by R feedback,

    Using Schmitt Inverter for clock ( and reset)


    Choices of supply, LED current and battery life are yours. This uses PC +5V.
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



--[[ ]]--