4017 & 555 Police LED Lights Project (noob question)

Discussion in 'Homework Help' started by 101010110, Feb 19, 2015.

  1. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    hello, i am assigned to create a physical project starting from the schematics on the left side. my teacher told me that the schematic is incomplete, so the first step is to corect it and then use pads and then send the gerber files to a company to create it. i started reserching it and every schematics i found on the internet about this project had a major diffrence...in my schematics the outputs of the IC 4017 is conecte to 6 resistors...on a number of other similar schematics they are connected to 6 diodes...this is my first project and it is the first time i have to use my electronics knowledge to do something from a tp z and aparently i don`t have much of it :(...can some one please talk to me about the diffrences on those schematics...can any one shed some light for me on this subject? i will be forever gratefull :) thank you in advance :) (sorry for my bad english, i hope you understand what i am talking about ^.^)
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Moved from General Electronics Chat to Homework Help.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What is the desired flash pattern for "police lights"?

    Are the flash patterns for both circuits the same?

    How do the two circuits create their respective flash pattern?
     
  4. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    how do i do that?
     
  5. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    he didn`t specify any particular flash pattern...i guess that is for me to decide
    i have no ideea if they are same...
    i don`t even know how to answer the last question...:(

    can you maby please explain how those questions are relevant and how dose the circuit differ when the pattern differs? it would help me alot
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You likely got the schematics from the following sites:
    http://www.electro-tech-online.com/threads/police-flash-lights.103089/
    http://www.555-timer-circuits.com/police-lights.html

    For the one with the resistors, what happens in the base of the transistor (look at the extra diodes 1N4148's).
    Why are no outputs of the 4017 skipped?
    For the one with the diodes, look how the signal would look like at the base of the transistors.
    Why are outputs of the 4017 skipped?

    Bertus

    PS MrChips did move the tread for you.
     
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  7. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    haha you are right about the 2nd schematics (the one with the diodes) as for the first one, that was given to my by my teacher... in the complete picture of the first schematics there is a link to www.talkingelectronics.com, but its the same schematics as the one on the electro-tech

    how do i "look " how the signal would look like at the base of the transistor...i`m guessing i need to simulate the circuit ? i`m thinking about doing it with orcad? that is the software we are using at my university...
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Only 1 pin of the 4017 will be high, all others will be low.
    With the resistor schematic, a voltage divider will be created.
    And what will the 2 diodes 1N4148 do in that schematic?

    What will happen in the diodes schematic?

    Bertus
     
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  9. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    i like the fact that you answer with tips and questions, this is great. as this is the first time i try to understand things not just to memorize things, it will take me some time to answer your question because i don`t even know how to abord the questions , i need to review some of my documentation and try to figure out how all that circuit works..! i will be back with answers
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    We need to introduce you to a member known as, Yakima. I am sure he will convince you of the errors in this perception.
     
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  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The first circuit uses the 555 to turn off the leds, at each clock pulse, your circuit uses every other output of the 4017 to put the leds on then off.
     
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  12. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    as i can`t think of any for myself i really would like him to explain his opinion on this aproach to me :D you really should introduce me to him
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here is the internal schematic and timing diagram of the 4017:

    [​IMG]

    This might give you an idea how the 4017 works.
    I also attached the complete datasheet for you.

    Bertus
     
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  14. 101010110

    Thread Starter New Member

    Feb 19, 2015
    14
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    uh uh i think i got it, i have major problems reading this schematics , i never know where to start "reading / interpreting " a schematics, but i think i partialy got this one...so here goes nothing, i`ll try to answer . so after i study the " counting action of the 4017 decade counter" i can see WHY "Only 1 pin of the 4017 will be high, all others will be low."...depending on where that 1high is ,1 of the 2 diodes will conduct current trough it...if 1 conducts current the other one is blocked , disableing the tranzistor that is wired to it, while the one conducting will create a flow of current from it`s transistor emitter terminal trough it`s base. wich will then enable the emitter - collector current to flow, thus lighting up the leds conected to it...is that corect? if not ask me more question so i can deduce why it`s not corect
     
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  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have made the question for the resistor circuit in a drawing, to visualize it:

    [​IMG]

    Bertus
     
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The 4017 moves the outputs one at a time from 0 to 9, only one output is high as it clocks the output moves along to number 9, your using every other output, so it pulses the transistor on and off via the diodes.
     
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  17. 101010110

    Thread Starter New Member

    Feb 19, 2015
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  18. 101010110

    Thread Starter New Member

    Feb 19, 2015
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    ok so i feel like when i have LOW the diodes will conduct SO the lights will be off...because the current will go trough the diodes, not the tranzistors...and if i have HIGH they will be blocked...and then magic happens and the lights are on....i wish i had a more engineering reasoning for this..this is just gut feeling
     
  19. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    no when the outputs are low the diodes are off, transistor is off, led is off, ...
     
  20. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When the input of the diode is low, it will conduct and the transistor can not be switched on.
    When the input of the diode is high, it is in reverse connected, and no current can flow through it, the current can go to the transistor, so the led will be on.

    Bertus
     
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