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LED Project help, please?

Discussion in 'LEDs and Optoelectronics' started by JayBlake, Apr 22, 2013.

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  1. JayBlake

    JayBlake

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    Apr 22, 2013
    I have been asked to help make an LED design work (because I'm a computer technician, it's assumed I am, ipso-facto, a guru in all things electrical).:eek:

    Truth be known, I'm great at fixing PC's and sorting out software issues but have no idea where to start when it comes to circuits, resistors, capacitors etc.

    I bought some bits'n'bobs from Amazon and ebay and am now the proud owner of Breadboard, LED's (various colours), mixed resistors and capacitors and even some 555 chips, cuz I don't want to let someone down, by being unable to help.

    I have attached a photo of the LED project and would seriously appreciate any help that could be offered by those who have probably already forgotten more than I could ever hope to know, in this.

    My task is, effectively, in two parts:

    1) Light up the LED's as per the attached plan.:eek::eek:
    2) Get them to flash on-and-off.:eek::eek::eek::eek::eek:

    I would be eternally grateful for help, pointers or other inspiration anyone might possibly extend to me in this.

    Many thanks for reading.
     

    Attached Files:

    Last edited: Apr 22, 2013
  2. john monks

    john monks

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    Mar 9, 2012
    Do you intend to use a computer to turn on and off the LED's?
    Are the LED's going to turn on and off to a particular pattern?
     
  3. JayBlake

    JayBlake

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    Apr 22, 2013
    Thanks for the reply.

    No, I want the project to be standalone and run from battery.

    No pattern, simply all on and all off repeatedly at, say, half-second intervals.

    LED's are 5mm diameter, I forgot to mention.

    :)
     
  4. duke37

    duke37

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    Jan 9, 2011
    121 leds at 20mA is about 2.5A if run in parallel. What battery do you suggest?
     
  5. JayBlake

    JayBlake

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    Apr 22, 2013
    Is that beyond normal batteries?:confused:

    We could always use a car battery, if so (unless it's also beyond that).

    Gosh, I wish I knew more about the fundamentals of this stuff.

    Just hope I'm not too old to learn.

    It's a very grounding experience to find that, expert though we might be in a particular field, just what novices we are in others.

    This is really taxing my grey-matter and I'm peculiarly pleased that it is.:)

    PS. Proof of my apparent ignorance is that I was half-way hoping we could run it off a couple of mini solar panels.:D:)
     
    Last edited: Apr 22, 2013
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    yes well beyond the avg battery, assuming you want it to run continuously for an hr or more
    You would get a good number of hours out of a car battery but its going to be needed to be charged every ~ 24 hrs for some hours.....
    so the questions are...
    1) how long at a stretch does it need to run ?
    2) do you really need it to be battery powered ? or can it use a power supply plugged into the mains?

    mini solar panels, definately not. to get in excess of 2 amps, in this case you would need a panel capable of at least 3 Amps ( for a bit of headroom) its gonna be a large panel costing probably at least ~ 300 - 400 GBP

    Dave
     
  7. JayBlake

    JayBlake

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    Apr 22, 2013
    OK, so if we use a mains supply (batteries would have been nice, but mains is an option), what voltage would I need and more importantly, how the heck do I wire the thing with all the resistors, capacitors etc (before I even start thinking about making the darned thing flash)?

    Am truly starting to feel a tad out of my depth, here, which is alien to me as I'm so familiar and confident in my own discipline of IT servicing. Fish out of water syndrome but am beggared if I'm not going to crack it.

    Thanks for your continued interest in my dilemna, everyone.:)

    PS. In answer to your first query, davenn, it won't be required to run for any long periods. Say, 1 minute or less in each hour.
     
    Last edited: Apr 22, 2013
  8. BobK

    BobK

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  9. JayBlake

    JayBlake

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    Apr 22, 2013
  10. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
    Why not use smaller LEDs and make it pocket size or is this gonna be used as a sign of some sort?
     
  11. john monks

    john monks

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    Mar 9, 2012
    Do you intend to use blue and white LED's?

    Blue LED's typically take about 3.6 volts.
    White LED's typically take about 3 volts.
    Red LED's typically take about 1.6 volts.
    Yellow LED's typically take about 2 volts.
    Green LED's typically take about 2.3 volts.

    If the LED's are all the same color you might be able to get away with connecting them up in parallel and that would simplify the wiring.

    Done right you might be able to run the whole contraption with 4 D cells.
     
  12. JayBlake

    JayBlake

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    Apr 22, 2013
    A sign (and if we can get it working at this size are hoping to even make it slightly bigger - maybe even double the size. But one step at a time, I guess!!).

    What I really need is for some guidance on just getting the perishers to light-up, in the first instance, without burning out the LED's or unduly diminishing their life expectancy.

    Am guessing I should aim for a 12v supply as that would facilitate either battery or mains power.

    The thing is, I've got all these resistors, capacitors, LED's and stuff and could really use some guidance on how to put them all together to achieve the required design.

    Can worry about making them flash, later.

    Thanks for your input.:)
     
  13. duke37

    duke37

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    Jan 9, 2011
    I think you should decide on the battery first.
    If the leds are to be switched on and off together then the circuit will be simpler than if they are to be sequenced.

    To run from 12V, you will need to have several strings connected in parallel.
    Each string should have several leds in series, with the voltages adding to 9 or 10V. A resistor should then be added to drop the 2 or 3V. This should be 50*Vdrop to get 20mA.

    If the leds are all coming on together, you could spend a few hours to optimise the distribution of the leds into the strings. Remember that convenience of layout will be important.

    Get one string working first.

    Polarity is critical.
     
  14. JayBlake

    JayBlake

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    Apr 22, 2013
    Hi John,

    The only two colours will be blue and white - as per the diagram I uploaded..

    So, do you know what voltage I would need for the entire project and would that need to be adjusted in order to make the lights blink?

    Many thanks.:)
     
  15. JayBlake

    JayBlake

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    Apr 22, 2013
    Can I mix the two colours (blue and white) in the same string or should I keep same colours together on each string?


    Cheers.:)
     
    Last edited: Apr 23, 2013
  16. duke37

    duke37

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    Jan 9, 2011
    You can mix the colours but if you make a mixed string first you can check on the relative brighness. 20mA is the normal maximum current but you may wish to reduce this if one colour is much brighter than the other. Obviously, the current is the same throughout the string.

    You could get 3 leds/string with 12v.
    121/3 = 40 strings plus an odd led.
     
  17. john monks

    john monks

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    Mar 9, 2012
    Just for a first approximation I would use a string of three LED's in series a 150 ohm resistor. You should try one string first just to make sure everything is connected right. You can used 4 D cells for your 12 volts.
    The voltages I gave for LED voltage drops are approximate but should be close enough.
     
  18. JayBlake

    JayBlake

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    Apr 22, 2013
    Thanks guys.

    This is proving far more challenging than I could have imagined - which is likely why I was roped-in as, being a "computer expert" (whatever one of those is), I fell for the "it will probably only take you a couple of minutes" line......:D:eek:.

    Needless to say, thanks for your continued support.

    No doubt, I'll be back for more advice soon. :)
     
    Last edited: Apr 23, 2013
  19. john monks

    john monks

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    Mar 9, 2012
    Don't drop out now! This a very simple project even for you. Just take three LED 's and one reststor and connect them in a string then hook both ends to a 12 volt source. You can use your car battery to start or even try a little 9 volt battery just to see if it works. And then when it does just string up the rest and connect them the same way on the batteries. If you work with computers you can do this.
     
  20. JayBlake

    JayBlake

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    Apr 22, 2013
    Thanks for the vote of confidence, John.

    Hopefully you are right and I have nothing to fear, except *fear itself.

    Thanks for the kick in the butt.

    *(of failure). :):)
     
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