Help making a 9v Flashing 47-L.E.D. Name Sign Circuit

Discussion in 'The Projects Forum' started by sloetyme, Sep 6, 2010.

  1. sloetyme

    Thread Starter Member

    Jan 13, 2009
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    Hi fellow members,

    I'm wanting to make a Name Sign for a friends daughter, per his request.

    I have worked out a sketch using 4 letters(her name) and a Heart. The circuit will require 47 - 5mm led's as you will see in the attached file[sketch.jpg]. This is just a sketch up.

    I'm not sure what type of driver to design. It needs to be at 9vdc(friend wants it put in to a picture frame). This needs to flash 1 sec. high and 1 sec. low. Possible voltage drop is based on 2.0v.

    I would like to hear some feedback from anyone experienced with this circuit. Greatly appreciated.

    Q&A's will be responded to within the evening hours(CDT). Thank You.:)
     
  2. tom66

    Senior Member

    May 9, 2009
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    The first approach to this would be to use a 555 timer as the oscillator, then feed this into a power device such as a IRF530 MOSFET. I'm not sure, however, that 9V would be enough to turn on a MOSFET (they usually require 10V.) Is it possible to use a 12V power supply?
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Two thoughts: 12 strings, 9 Y, 2 R, & 1 R&Y = 180 mA @ 15 mA /LED, with 68Ω in Y & R strings & 200Ω in mixed string of 3 LEDs, others 4 LEDs.
    OR: Alternate name & hart @ 150mA-name & 45mA-hart. 555 would drive directly. Driving 180mA, all on- all off might be pushing 555 200mA rating.Also consider 1 sec on 2 or more sec off to conserve battery.
     
    sloetyme likes this.
  4. tom66

    Senior Member

    May 9, 2009
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    A question; are you planning to run this off a 9V (transistor/radio/smoke alarm) battery? It won't last long on that, the 9V batteries have very small capacities. 3xAA would probably work better.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    It is more than doable. What is your experience level? If you have the experience soldering you could use surface mount and make it very small, I just bought a batch of 2N2222A transistors for 4¢ each for example.

    Since yellow drops around 3.0VDC you can only have two per chain, which is a pain.

    Can you consider going with 8X AAA batteries (10 is better)? They will have more amp hours overall. You could could drive them better.

    Here is a little article I wrote for beginners.

    LEDs, 555s, Flashers, and Light Chasers

    Another possibility is something like this...

    CMOS 555 Long Duration LED Flyback Flasher

    It would drive more per chain, requiring a transistor/coil for 8 or so LEDs. The blue LEDs can be replace by yellow.

    I'm about to go to work, so I will pick this up tomorrow morning.
     
  6. sloetyme

    Thread Starter Member

    Jan 13, 2009
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    Thank you for the help. I was leaning towards the 555 theme but like some of know 200mA would be the max, and 47 leds would be about 240mA. As for the 530's, I have a hand full of them and wanting something to do with them. Also the reason behind the 9v batttery is really open to other ideas, just no cords to be plugged in the outlet(child proof room).
     
  7. Ghar

    Active Member

    Mar 8, 2010
    655
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    They require 10V to achieve the specified on-resistance.
    Their threshold is anywhere from 2 to 4V and they will conduct.

    Exceed the threshold and the transistor will be on decently well, it's just a question of on-resistance. 9V is almost at that good spot.

    With the milliamps of current required by the LED's it really won't be an issue.
     
  8. sloetyme

    Thread Starter Member

    Jan 13, 2009
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    Yes I'm trying to decide maybe * x AA or * x AAA. I think your idea is good just wondering with 4.5 volts into a 555, would i still be able to send out enough mA for an array and transistor to work?
     
  9. sloetyme

    Thread Starter Member

    Jan 13, 2009
    11
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    Your info is a lot to absorb but to the point. I'm gonna toss around some of the info you supplied to us and myself as well, and see if i can produce a design and see what ya think. Thank you for helping.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    The real problem you have is size of the parts, and battery life. Thinking about it it can be done simpler. You didn't list the size of the name tag, this is the footprint you have to work with.

    You need more voltage, not less. 4.5 volts will only power one LED per chain, which will drive your current requirements through the roof. The long duration LED flyback flasher can over come this to some extent, but your battery life is going to be limited.

    I know you figured 2.0 volts drop, but this is only if you have older LEDs. New LEDs are different, modern yellow is around 3.0 volts drop, which is where the number I selected came from. Violet will drop a large amount, anywhere from 3.5 to 4.0 volts. Since this is a new color for LEDs you won't find any older LEDs that use less.
     
  11. sloetyme

    Thread Starter Member

    Jan 13, 2009
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    Thank you Bill!

    I like your idea of 8 x AAA or 10 x's. I'm thinking about the Astable Multivibrator. Would this work?
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    Yep. There are so many way to do this it is wide open. Here are the problems you have to overcome.

    1. Footprint. It is going to have a boat load of transistors/resistors. If you have the experience surface mount technology will solve this.

    2. Chain lengths of LEDs. If you actually have 2.0V LEDs it will simplify your life, but they are rare because of age. At 15V (X10 AAA batteries) you could have 6 yellow LEDs at 2.0V or 4 yellow LEDs at 3.0V. Each chain requires a resistor, but I suspect you can use one transistor.

    I think I asked this, but I didn't get an answer. What is your experience level? You will have to do some fine soldering for it.
     
  13. John P

    AAC Fanatic!

    Oct 14, 2008
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    Maybe you should consider specialized LED driver chips, or you could make your own. The advantage of these over a simple resistor is that they're designed to step up from a low voltage to a high one, to the point needed to run multiple LEDs at a particular current. That way you can run your setup off a lower voltage (i.e. no need for a whole bunch of cells in series) and you wouldn't see much change in brightness as the batteries run down. Plus you could drain the batteries until they are almost dead flat, rather than having to change them when the voltage can't drive the LEDs any more. But yes, it's more complication. There's always a price to pay!
     
  14. tom66

    Senior Member

    May 9, 2009
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    I think everyone is complicating this too much.

    Just get some stripboard and some cheap signal LEDs. Then use resistors on pairs of three or four. Most red, yellow and green signal LEDs will light well from a 2V supply. Use a 555 timer for the oscillator. Then use a transistor, preferably a MOSFET but an NPN would also work well (e.g. TIP31.) Power it from a 9V plug pack or 6xAA (=9V). Done.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Actually I'm not. It's the quantity that is the issue. If we can get the voltage up a 555 might be able to handle it. Name tags tend to be small, which is why I'm going on about footprint.

    We have to have 2 things.

    The voltage drop of the yellow LEDs and the max current.

    The voltage drop of the violet LEDs (or are they blue?) and the max current.


    You don't have to use maximum current, there is no requirement for such. You could easily use 10ma for the LEDs. If they are old yellow types 10ma may be their max current.
     
  16. tom66

    Senior Member

    May 9, 2009
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    I think it's a big risky trying to power it all from the 555 timer. Although they are rated for 200mA this is a maximum rating only. The timer drops about 1.5V on the output for bipolar variants.

    One configuration would be to use 5 LEDs in series from a 12V supply. At 10.5V, each LED would get 2.1 volts, which is fine. You could put about 50 LEDs on the output, but this would be getting mighty close to the limit of 200mA.
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    We don't have enough information for any assumptions yet. Now you're over complicating things.
     
  18. sloetyme

    Thread Starter Member

    Jan 13, 2009
    11
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    Wow, sorry for the complicated mess i have made.:) I like how you all are thinking. You have a lot more experience than me.

    My experience level is that of a beginner.
    I can work with smd but on the other hand I would like to use the 530 fet's which are through hole.

    Finally, I'm gonna make up something, not sure what, then i'll post it and tell you about the circumstances i have found. I have a Ir thermo gun too to test the heat.

    Tonight or first thing tomorrow night I'll get back here with the results. Thank you again for the input from you all.
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    You'll likely only need one MOSFET. They also make some decent logic level units, which doesn't apply if the power supply is 12V or above, which is where conventional MOSFET work. Logic level MOSFETs will work with much less voltage.

    Most MOSFETs don't even get warm carrying several amps.

    Like I said, all we need now is the LED specs.
     
  20. sloetyme

    Thread Starter Member

    Jan 13, 2009
    11
    0
    Sorry I haven't made it back sooner, I will be a bit longer though, I'm keeping things afloat around here with the loss of a loved one. I'll be back as soon as I can. Take care and check back maybe on the 18th should be back by then. Thank you.
     
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