Flashing LED project help, please.

Discussion in 'The Projects Forum' started by JibTeenuc, Oct 11, 2013.

  1. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Hi everyone,
    First time poster (please be gentle).
    I have a small(?) LED project and not the slightest idea where to start except in that I have researched what I believe I need and am armed with Soldering Iron (which I am used to) along with stuff I’m not used to as follows: Breadboard and cables, battery holders, AC/DC power adaptor, a shed-load of 5mm Ultra-Bright LEDs, Resistors, Capacitors, Diodes, Ne555 and Ne556 chips, Crocodile clips etc., etc.
    I currently have no idea how to read an electronic schematic diagram (but am reasonably confident that I can learn).
    I want to produce an up/down, flashing, LED sign and have attached my own (non-schematic) diagrams of what I hope to achieve.
    I have no idea whether this is a simple or a difficult project, I am so “green-behind-the-gills” and do not even understand the advantages or otherwise of running the proposed LED project in either Series or Parallel mode.
    I would wish to power the project from either AC/DC adaptor or a 12 volt car battery and only for very short (on-demand) periods of time, similar to how often the button is pressed at a Pedestrian Crossing, say.
    Is anyone able to offer any help and advice, please?
    :)
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Figure A seems better to me because it uses fewer LEDs in total, and the wiring scheme is simpler. However, connecting the LEDs will be tedious and time consuming. The first thing needed is the forward voltage of the LEDs and the current rating; this may be different for the red versus the yellow.
     
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  3. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Thanks for replying.

    For simplicity purposes, I've had a colour rethink and would prefer the red LEDs to be replaced by blue and the yellow LEDs to be replaced by white.

    Each has a forward voltage of 3.2 to 3.8.

    The supplier states the current requirement as being 20mA (typical) and 30mA (max).

    Ideally, I'd like to power from a 12v car battery and I've experimented a little with an AC/DC adaptor set between 3v and 12v (with suitable resistors) to no obvious ill effect on batches of random blue and white LEDs.

    Hope that helps. :)

    Thanks again.

    Jib T
     
  4. tracecom

    AAC Fanatic!

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    Given a 12VDC power supply, you will have to arrange the LEDs in strings of three LEDs; each string will need a series resistor of 62 ohms (1/8 watt or larger) to allow a current of just under 20mA.

    With 44 strings (132 LEDs) being the most that will be lit at any one time, you will consume 880 mA; thus your power supply should be rated at least 1.5 times that, or about 1.32 A or more (2 A would be good.)

    There would be a total of 62 strings of LEDs, plus one LED with its own 430 ohm current limiting resistor. Each of the 62 strings would be wired as shown in the attachment; note that the resistor can be physically located anywhere in the string as long as it is in series with the three LEDs.
     
    Last edited: Oct 12, 2013
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  5. #12

    Expert

    Nov 30, 2010
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    typo: "1/8 watt or larger"
     
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  6. elec_mech

    Senior Member

    Nov 12, 2008
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    Welcome to AAC.

    Could you walk us through, step-by-step, how you'd like the display to function?

    Example:

    1. Using a latching toggle switch (ON-OFF-ON), all LEDs are off when switch is in center position.
    2. When switch is in one on position, three arrows are lit as shown (attach picture here) and LEDs: a) stay lit, b) flash, c) do a) or b) depending on position of another switch?
    3. When switch is in opposite on position, . . . ? (provide picture showing what is lit on display)
    4. Other features, e.g., flash for xx seconds and shut off, etc.?
    As this is a display, what is the closest and farthest you expect the user to be from the display and still see it? Will users primarily be looking at it head-on or from an angle? If the latter, what is the maximum viewing angle (angle relative to looking at the display head-on). Will this be located indoors or outdoors? If the latter, will this be viewed during the day in sunlight, at night, or both? Answers to these questions impact which type of LEDs will work best for your application.

    Could you elaborate on the goal/purpose of the display?
     
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  7. tracecom

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    I haven't built this, but I think it would do what you are requesting.
     
    Last edited: Oct 12, 2013
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  8. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Wow, tracecom.

    If I could issue a profanity on the board, I would.

    That, to me, is awesome.

    Do you mind if I take a day or two studying it (as I said, I don't read schematics...but I think I'm about to go through a steep learning curve).

    I'm bound to have more questions (being a newbie to all this). The first being that, having done SOME research prior to posting my initial question is "how have you done that with a 555 as opposed to a 556 chip?" I had envisioned using 555 chips for two separate panels and a 556 chip for one "all-in" panel (excuse my ignorance, I'm just surprised is all).

    Many, many thanks for your design.

    If this ever goes commercial, you're more than just on the team!!!

    Jib T
     
  9. #12

    Expert

    Nov 30, 2010
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    Just smart, I guess.:p
     
  10. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Hi elech-mech (thank you for the welcome. I do feel at ease here),

    Thanks also for your considered and detailed questions which are just what I need to help me explain the project in my head to others (who don't have access to my head).

    It started out as a fun experiment of a directional sign for my daughter's project, but I am hoping it could even go commercial with some tweaking, yet who knows??

    Thanks again for your input:)

    Jib T
     
  11. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    I so wish I were, at this stage in my learning.

    Computers??? Piece of cake.

    REAL electronics????...May as well be rocket-science.

    :)
     
  12. tracecom

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    Apr 16, 2010
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    The compliments made me paranoid, so I breadboarded the circuit. It works as I hoped, but in looking over the schematic, the two 1N4148 diodes (D2 and D3) will be overstressed with powering 77 LEDs, so I have changed them to 1N4001. The MOSFETs are overkill, but they are what I keep in stock; BS170s would probably work, but they would be at their max. In addition, the component count could be reduced by one resistor by moving R3 to the wiper of SW2, and eliminating R4.
     
    Last edited: Oct 12, 2013
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  13. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Thanks, tracecom.

    Not wishing to be a nuisance but is there any chance at all that you could upload a snap of your breadboard circuit, so I can see if I can figure out how to tie the schematic to the physical?

    Also, I have some fiberglass PCB boards which, as I obviously don't want the resistors etc showing with the LEDs, should I attatch to the underneath or adjacent to the LEDs, on the top?

    SO many questions (many of which must appear "bleedin' obvious", I'm sure), when just starting, I know - hopefully not too many!

    Thanks again.

    Jib T
     
  14. tracecom

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    Here is a photo of the breadboard; it's not my best construction, but I was in a hurry last night. There are better ways to arrange the components. I left the photo in relatively high resolution so you could see the details, and attached a lo res version if you have limited bandwidth.

    Notes about the photo:
    1. There are two 100Ω resistors (R3 and R4) from pin 3 of the 555, one each to the gates of the MOSFETS. One of these can be eliminated as previously documented.
    2. There is no SW2 on the breadboard. I just connected and disconnected R3 and R4 to simulate the switch.
    3. D2 and D3 are 1N4148; in the final assembly, they should be 1N4001.
    4. The green LED represents Group X, the red LED represents Group Y, and the yellow LED repsresents Group Z.
    5. There is no SW1 on the breadboard; on/off switching is done with the switch on my regulator module.
    6. On the breadboard, all black wires are ground, all red wires are +12VDC, and all other colors are signal wires.
    7. On the 555, the white dot is pin 1.
    8. On the MOSFETs, the pins from l to r are 1. Gate, 2. Drain, 3. Source.
    9. I just noticed in the photo that one of the MOSFET gate pulldown resistors is 15k instead of 10k, but it doesn't matter.

    As elec_mech has said, you would get better information if you stated the functional purpose for this. There are lots more creative things that could be done using a micro-controller.
     
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  15. elec_mech

    Senior Member

    Nov 12, 2008
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    Ah, sorry, I didn't look very hard at the second and third attachments from your first post - I see now which LEDs you want lighted when.

    Tracecom's circuit should give you the ability to get your half second on and off flash requirement.

    As far as the physical circuit is concerned, we suggest you begin by building your circuit on a breadboard as Tracecom has shown. Once you've verified your connections are correct and the circuit works to your liking, you can easily put this circuit onto a proto board where you can solder the parts and make a permanent circuit.

    The circuit will be separate from the LED display board. You can mount the circuit board on the back side of the LED board, but given the number of LEDs, you won't mount the LEDs and circuit to the same board. I'm assuming you're planning to use 5mm LEDs? If so, you can either use a proto board or simply mount the LEDs directly to a piece of wood or plastic. If the LEDs need to be spaced as close together as you've shown, the protoboard may be your only option. If they can be spaced 6mm or more apart, I personally like using 1/8" (~3mm) thick PVC as it is easy to drill, but acrylic works well too - just be extra careful when drilling otherwise the acrylic will crack. It's easy to bend the LED leads together and solder the LEDs that need to go in series. From there you'll solder wires to the LEDs and your circuit.

    Do you have approximate dimensions for your display?

    Based on the distance, you shouldn't need overly bright LEDs or LEDs with a wide viewing angle, but the daylight requirement may change the former. Do you plan to add a cover over the display - much like you see over stop lights? This will act like an umbrella to shade the LEDs from the sun so they will not need to be as bright.
     
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  16. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Thanks for your continued support and inconveniences along with that of elec_mech for his interventions.

    My brain is spinning (I had envisioned it all being a smidge easier than it is but, being a computer technician by trade for in excess of 3 decades - hardware, software and more recently Web-Design etc., but NOT electronics, I'm reasonably confident I'll get my head around it....EVENTUALLY! Even if much of it is currently just beyond my cerebral reach).

    I know you guys are probably busy with other things and your own projects but, if you will indulge me, the answers have already thrown up a couple of queries that I shall try to formulate into coherent enquiries.

    Thanks so much, again, for all your experienced help.

    Jib T.
     
    Last edited: Oct 13, 2013
  17. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Thanks for your help, E_M.

    I hope my replies, above, help clear things up a little. It's awkward describing an idea when I'm still currently ignorant of the relevant terminology/language.

    Pic #1 shows the pre-drilled proto board I posses, which is ideally sized for this particular project as it stands currently (although I do envisage making the sign larger, at some point in the future).

    Pic #2 shows the same board but loose-populated by an outline of the required LEDs being 11 wide x 17 high.

    Comment 1: Do you know what? You are so right in this in that I've even been planning to diffuse the LEDs with Glass Frosting Spray in order to lower the brightness (or even with a plastic/perspex light-diffusing-cover). Dunno why I was so gung-ho about using Ultra-Bright LEDs (apart from the fact that they sound sexier than regular LEDs):D

    Glass frosting spray: http://www.amazon.com/Rust-Oleum-1903830-Frosted-Glass-11-Ounce/dp/B0009XCKBA

    Comment 2: No real need as, although I want the panel to be visible in daylight as well as in the dark, I don't envisage direct harsh sunlight directed at it.

    Thanks again for your help which is greatly appreciated and I hope you don't mind if I seek to pick your brains again, in the future.

    It's quite lonely, doing this on my own :(

    Jib T
     
    Last edited: Oct 13, 2013
  18. tracecom

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    Apr 16, 2010
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    Look at the drawing I attached to post #4. You will need all the LED strings to look similar to that. Most will have 3 LEDs and one resistor, but there will be one string in group X and one in group Z that will have only 1 LED and 1 resistor. In group Y, there will be one string with two LEDs and one resistor. Look at the PDF I attached to post #7.

    Notice that one end of each string is connected to +12VDC and the other end is connected to ground. Then look at the schematic and notice that it shows +12VDC connected to every LED string all the time, and that what is being switched is ground, with a separate ground connection for each of the three LED groups.

    So, all the LED strings will have their anode side permanently connect to +12VDC, and each of the three groups will have its own ground connection to the cathode side. Thus, you will need four wires from the control board to the LED board: +12VDC, ground X, ground Y, and ground Z.
     
    Last edited: Oct 13, 2013
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  19. JibTeenuc

    Thread Starter New Member

    Oct 1, 2013
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    Thanks for replying so quickly.

    I must confess that much of this may as well be written in Cyrillic Script to me, at the moment (but, hey, I can learn Cyrillic I reckon :)).

    Time for me to stop talking and start walking I think (time to actually start physically building the ruddy thing, in other words).

    Not looking forward to the trip-ups I'm bound to experience on the way but am looking forward to the challenge of better understanding a little of your world and achieving my goal - sooner rather than later, hopefully.

    Thanks for your patience. If I get to the hair-tearing stage, at least I know there's help "out there", now. :):)
     
  20. tracecom

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    Just build the NE555 astable multivibrator section first; that's everthing to the left of SW2 in my schematic. When you have that built, post again, and we'll go from there. You can do it. We can help. (Seems like I heard that on TV...Lowes maybe.)
     
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