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Electronics Pulsing LED Schematic?

Discussion in 'Modding' started by Zacrobmer, 4 Aug 2010.

  1. Zacrobmer

    Zacrobmer What's a Dremel?

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    I had plans on building a pulsing LED circuit for my inprogress case mod. I have all the parts to build the one that was on http://www.rabidhardware.net/index.php?id=5 however, that site has since been shut down (within the last couple of weeks). I can pull the cached site from google, but the images are missing. Most sites I can find link back to the Rabidhardware site.

    Does anyone know of another site that may have that same schematic? Or does someone have a copy of that schematic saved somewhere?

    Here is the parts list.....

    LM1458N op-amp
    2N3904 NPN amplifier
    22uF 100V capacitor
    4x 47K ohm 1/4w resistors
    2x 100K ohm 1/4w resistor
    100 ohm resistor
    Molex connector

    Any help would be greatly appreciated.
     
  2. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    When you say 'pulsing' do you mean like fading on then fading off?

    If so, I can draw you something up pretty easily with those parts...
     
  3. Timlander

    Timlander Simm Saver

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    Hmm I may actually be interested in this as well. I await your schematic Pedro. I was always bad as electronic engineering.
     
  4. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    Well if there's interest...

    [​IMG]

    Something like that should be what you're after I reckon. It's a triangle wave generator set up so the LED will fade on and off (rise time = fall time).

    The LM1458 needs +12v on pin 8 and GND connected to pin 4 but the part in EAGLE doesn't bother showing those pins.
    +12v is the yellow wire in the molex power cable. GND is the black one.

    The 2N3904 can handle up to 200mA, so you should be able to run a few LEDs off it if you want, but with R4 being 1/4W (I assume), I wouldn't put more than two or three in series before starting to run groups of 2 or 3 in parallel with each other. But that means you need multiple 100R resistors.
     
    Last edited: 4 Aug 2010
  5. Timlander

    Timlander Simm Saver

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    That didn't take you too long, you must do this for a living. :D I plan on incorporating a lot of LEDs into my next custom case build. What do you think the best way to do this would be? I was thinking having a main 12v power coming from a molex connector on the PSU with a 510ohm 1/4watt resistor connected to one of those main power leads. Then have multiple strings of LEDs run in parallel off of that main power? Would that work well or would the LEDs dim down due to current lose? I understand the basic fundamentals, but when I need to actually design or build a circuit from scratch, that is where I have troubles. If need be I can make a new thread for this, but I figured since it was related it may be worth asking here.
     
  6. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    You probably won't be thinking that when you realise I had to edit my post between you seeing it and replying because I mucked something up!

    I realised why there were a couple of spare parts for a start! :hehe: If anyone's interesting I forgot there needs to be a differential between the integrator op-amp's supply and the comparator's. Hence the voltage divider! Amateur hour, or what.

    And no, this isn't what I do for a living, but I will be starting a university course soon, so hopefully in four years time I will be a professional electronic engineer.

    Have a play around with this LED calculator tool. You want to have as small value resistor as possible really because all the resistor is doing is making heat. It's a bit wasteful. Four groups of three series LEDs would only need one resistor per group of three and each one would only need around 100 ohms so there's 12 LEDs needing only 400 Ohms of resistance total. You can only run a couple of LEDs off each resistor before the resistor has to dissipate too much heat and burns up (especially for a 1/4W resistor), so while you could use one huge (5W or something) high resistance resistor, you're much better off using a few smaller ones.
     
  7. Zacrobmer

    Zacrobmer What's a Dremel?

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    Yes, pulsing would be correct.

    I found the electronic schematic, the Rabidhardware site had a color coded "idiot proof" version.

    Here is the actual schematic.

    [​IMG]


    Any chance someone could make a color coded wiring diagram? Something a bit more idiot proof?
     
  8. Timlander

    Timlander Simm Saver

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    Mistakes happen, its a good thing you caught it so fast. =) This can be some pretty complex stuff, iv taken a few courses in it and let me tell you I would never want to do this for a living. Good information for the LEDs there thanks, that information will be put to some good use soon enough. :thumb: Dang so I guess I need to get some new resistors, at least these 60 510 ohm ones were free haha. :D

    Looks a lot like pedro's one now. I dont know if I could do an idiot proof schematic since im not too great at this stuff either, maybe someone else will come along for that one. If not you could always google. :D
     
  9. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    Yeah, that's pretty much exactly what I was thinking of. Although with some further thought (jeez, why do I always think about stuff after I publish!?) your transistor will probably be in saturation all the time (so no fading) unless you power it from +12v as well so R4 would need to be a higher value.

    That diagram's a bit more convenient, excluding the fact that there's no 9v source in an ATX power supply. It would be nice, though because your fade effect would be more pronounced - the LED might switch all the way off on its fade out cycle in fact.

    Having a look at that's given me a few ideas and I've had chance to play around on a breadboard. Here's what I've got:

    [​IMG]

    12v is too much but 5v isn't enough juice, so we use a ghetto 7v supply (we use the +5v instead of Gnd. 12-5=7 so we have a 7v supply instead of a 12v or 5v one. "Just right," said Baby Bear.). Usually I'd do this with a zener diode or linear regulator, but I'm trying not to use any extra parts for you.

    What sort of colour coding scheme were you wanting? Circuit diagrams are pretty easy to understand. Integrated circuits (the dual op-amp) have their pin numbers starting at 1 in the top left (by the dot/notch) and go round anti-clockwise.
    [​IMG]
    The pin numbers are labelled in the schematic (the two triangles are part of the same IC).

    TO-92 transistors are like this:
    [​IMG]
    1: To the LED's anode
    2: To IC1 Pin 1
    3: +12v

    The white line down the side of electrolytic capacitors indicates the negative (cathode) wire, which in this circuit goes to pin 2 of the op-amp.

    LEDs (and diodes in general) only work "one way round". The long leg is the anode (positive side) which here goes to the 100R resistor coming off the transistor's pin 1.

    Resistors go in either way round.

    Green lines show where connections are to go. Crossed wires with a dot are joined, crossed wires without the dot are just passing over each other - there is no electrical connection.

    I've tested the circuit diagram in this post. Here's what it looks like when made:


    I have to say my £20 phone's camera is fantastic...
     
    Last edited: 4 Aug 2010
  10. HowY

    HowY What's a Dremel?

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    Arduino

    Actually if you can write just a little code [in c]
    grab a cheap arduino knock-off it makes LED's
    sing an dance PWM and digital hi low.

    Easy to program and lace up LCD's for info
    and many (many) strings of LED's.

    Not stuck with charge/discharge rates w/cap-resistor
    or fixed Freq's so strings can randomly light and fade
    and actuate other circuits.

    moderndevice is a good source and the whole
    platform is open source with good community support...

    The official Arduino site but there are tons of avr's...
    I use the bare bones... 20 bucks -- less if you want to sweat
    it up manually. The only real cost is the ftdi cable at 20 clams.
    Off the shelf cable
    or you can build one - search for some guides.

    Great platform no one here seems to have taken too

    Check 'em out :rock:
    [I've no affiliation with any of these vendors]
     
  11. Zacrobmer

    Zacrobmer What's a Dremel?

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    Thanks, this schematic actually makes it a bit easier for me to read, as it "opens" it up a bit. I will be using a 7809 linear regulator to drop the voltage to 9v. I have several from 10-5v lying around from experimenting with a homemade relay switched fan controller.

    I have a pretty good array of parts lying around and am pretty handy with a soldering pen, as long I can understand the schematics.

    I am almost wondering if I can swap the 100k resistor and add a potentiometer to change the pulse rate?

    Thanks for the assist! I will probably bother you in event I can not get it to work!
     
  12. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    For more elaborate lighting effects I'd be with you on this one. I've always liked the Atmel ATMicro and ATMega chips and the Arduino platform is fantastic, but for fading a single LED at a fixed rate this is complete overkill.

    That sounds like a good idea. It's kinda unnecessary as you can get the circuit to work off 7v with a virtual ground (in the demonstration video I'm just using a 12v and 5v supply and it works just fine) but it's a little less hackish to have a true 0v Gnd, I suppose.

    You would need to swap C1 for a trimmer capacitor in order to change the "on time" of the LED, but they aren't available in anything near 47uF.

    For a circuit with a variable rise/fall and/or on/off time, you'd be better off using a small microcontroller like HowY suggested. Probaly an AtTiny13A. But then you need to learn how to program micro-controllers and buy an ISP programmer. The circuit itself would be much easier, though.

    Without using a uC, you'd probably want to use a waveform generator IC to make a configurable triangle wave/sawtooth to drive a transistor.
     
    Last edited: 4 Aug 2010
  13. japala

    japala What's a Dremel?

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