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LED Mods

Discussion in 'Hardware, Setup & Repair [BG]' started by bassist4ever, Jul 21, 2002.


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  1. bassin4him

    bassin4him

    Apr 29, 2002
    Tulsa, OK
    You may have found one of many solutions to dimming an LED, but you still haven't solved how to get a signal from the volume or tone pot that can be used to "tell" the LED dimming circuit how bright the LED is supposed to be.

    A possible solution, in fact the only one I can think of right now, is to install another pot in tandem with the volume (or whatever pot you want the LED intensity to correlate to). The likely problem is the guitar body may not have the depth to accomodate the extra pot.

    Looks like everyone is enjoying solving this little problem! Keep at it!
     
  2. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    I agree, bassin4him , I kind of backed off because I felt like everyone must have assumed that I was grabbing at straws.

    Stacked pots would solve the problem if that were the only problem.

    I worked in the R&D department of a major company that specialized in industrial motor brakes and A.C. motor speed control devices (Electrical South Inc.).

    My job was debugging the designs that the engineers developed.

    The engineers jobs were to develop a concept and my job was to make thier concept actually work in the manner that was intended.

    My biggest challenge often was convincing the front office that just because a circuit moved in the right direction that it fell short of being usable for the intended purpose.

    If a motor speed control worked within a narrow range but a component always blew out after three or four duty cycles, it was often very difficult to convince the shirts that it was a faulty design.

    That is exactly what we are dealing with in this case.

    As, I'm sure you know, the simplified circuit that Merl has come up with is a linear control circuit that is trying to control a non linear parameter.

    The pot is only controlling the hysteresis of the leds' turn on/off voltage. Approximately .4 to.7 volts depending on the particular LED.

    It is nothing more or less than a precarious balancing circuit that doesn't take into account any change in parameters that occurs in the individual parts as a result of temperature changes in each individual part.



    The only way that I can effectively argue my position is to do so with someone who understands the "mechanics" of a solid state junction.

    I could point out several reasons why the circuit is faulty, the least of which being the fact that there is a steady 40 MA (appx)drain on the battery at all times. Either on or off. There is a 2K resistor directly across the battery. That's not even counting the current draw of the LEDs

    A sample testing of several LEDs will show that the precise operating parameters will vary from LED to LED even within a given family(part numbers) of devices. It would be pure luck if they all turned on and off in unison.

    The idea of using different colored LEDs doesn't address the fact that different colored LEDs have different junction voltages thereby requiring different settings for the 2K pot. That would ensure that they wouldn't work in unison.

    The reasons why it wont work go on and on.

    Bottom line is this question: will the circuit work properly for this intended use?

    The answer is NO. not even close.

    The original question was " how can I do this". Merls answer doesn't address the question.

    One can juggle resistor values untill one turns blue in the face and the circuit still wont accomplish the desired result.

    With all due respect, Merl, I disagree with the statement that "electronics is easy".

    I close, (for the moment :) with this question: Why do the manufacturers of LEDs (as far as I can determine, ALL of them)suggest a PWM circuit
    to dim an LED(s).

    Again, Merl,I say: If you think I'm wrong try it. Don't just try it untill you get a result that appears to support the argument in your favor.

    A properly working circuit should fit these parameters: Linearly dim and brighten the Led(s) through the full range of the pot. Not exceed the physical limitations of any of the parts. Be repeatable with commonly available components.

    Whew, Pkr2

    Addendum: This is still all in fun Merl. I truly admire your determination.:)
     
  3. No matter the answer to the problem, it is always useful to remember the question. Bassist4ever doesn't want to dim an LED with a signal from a bass, he only wants to dim it with "a knob" on his bass - read his original question above.

    The other (and much more useful) addition is an LED indicator for pickup selection. That might be easier.
     
  4. bassin4him

    bassin4him

    Apr 29, 2002
    Tulsa, OK
    pkr2, I agree with you totally. It may be painful to acknowledge that a super-simple pot/resistor solution will never yield a satisfactory result, but my 30 years of ee design experience lead me to conclude that it is not good solution, unless one defines "a satisfactory result" very loosely.

    The PWM method, even though it's a little harder to understand and a bit more complex, has been used in countless applications and is well proven as the preferred method of LED dimming.
     
  5. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    The second part of the question requires almost no knowledge of electronics, Hambone.

    A knowledge of very simple basic electricity is all that's needed. Simply turning lights on with a switch.

    The second part is the part that gets a bit "hairy".Whether the pot is ganged with another pot or not, the same theory will still apply.

    As I said in my first post: Switching lights is easy. Dimming an LED (I should have inserted the word "effectively" here) is HARD. :)

    Pkr2
     
  6. bassin4him

    bassin4him

    Apr 29, 2002
    Tulsa, OK
    You're right Hambone! I read into the post that bassist4ever wanted to correlate LED intensity with one or more of the regular bass controls. My error.
     
  7. Howdy!

    have you built the simple circuit Pkr2? I figured that Bassist4ever is after something that looks interesting. Sure the LEDS don't dim in a pure linear fashion, and they don't all dim exactly at the same time. But they do dim. Or at least it gives that impression to the eye.

    I think that this is great, really proving a theory, and i do wish to continue, but lets not forget the purpose overall. Sure, sure if we (we as in us EE freaks) saw a bass guitar with dimming LEDS we'd ask the owner "hey how did you get that to work?" the answer most likely "errr well i put a battery in this morning......???" :p

    On the constant drain, i feel i have accomplished one of the design paramters to some extent, the second part involved the switching of them, using a "pick-up" selector. Even so, make one of the options of the switch to disconnect the battery from the circuit. Because when he stops using the bass... the LEDS would stay on otherwise. ;)

    As Hambone pointed out.... the original question didn't ask for it to be signal controlled. If that was the case then wouldn't the LEDS be turning themselves on and off??? Postive half cycle/negative half cycle of the signal.

    So yeah.. hmmm memory lapse... run out of things to say! Try building it and see where i am coming from?? I had the bits lying around on my bench... i reckon you guys do too! :p

    :D:D

    Objection!! SUSTAINED.... haha
     
  8. guys. i am pretty dumb about electronics. all i know about is speakers. and stuff liek that.. so if anyone would be kind enough to post a full schematic using BASS pots and stuffmaybe i could get it to work.


    thanks again guys
     
  9. That'll happen when we all agree on a design. heehee know this.. when we do, it'll be pretty good, especially with Pkr2 and Bassit4him no doubt!

    Me? I just try things lol.

    :D:D

    Merls
     
  10. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.

    No, I haven't made up the circuit. It is a very common basic cookbook circuit so far as the pot and resistor are concerned. Totally predictable.

    Leds are also totally predictable insofar as applying voltage to them. The combination of parts in your circuit is also predictable.

    I'll bet that I wasn't wrong when I described to you how your circuit behaved.
    ----------
    The dimmer circuit and the switching circuit are two completely different circuits.

    For the sake of clarity, we are only discussing the dimmer circuit.
    ---------
    "If that was the case then wouldn't the LEDS be turning themselves on and off??? Postive half cycle/negative half cycle of the signal."

    That's kind of close to how a PWM circuit works. Difference being that PWM doesn't use an input waveform for control.

    Pkr2
     
  11. theory was spot on. And yes in practical circumstances theory=practically. But i am sitting here with the circuit knocked up on a breadboard and adjusting the pot watching them fade as i turn it down, and then brighten as i turn them up. I think thats what he was after. ;) So i am a little confused when u say it couldn't possibly work. Sure it doesnt work over the whole range of the pot. But they do fade. :p

    :D:D

    Merls
     
  12. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Originally posted by bassist4ever
    guys. i am pretty dumb about electronics. all i know about is speakers. and stuff like that.. so if anyone would be kind enough to post a full schematic using BASS pots and stuffmaybe i could get it to work.

    ------------

    I'm sorry but I don't think I can suggest a circuit that will reliably dim an LED that would be suitable as a DIY project.

    If I may make a suggestion, why not use flashing LEDs. It would probably be much simpler and more eye catching.

    By using a couple of AAAA batteries, you could probably tuck them into the control cavity with room to spare. Maybe make a flashing array into a thin pad that you could just stick on the front of your bass. No mods to the instrument that way.

    Pkr2
     
  13. you getting tired of this Pkr2!! heeheehee

    Don't bail on us now. ;)

    :D:D

    Merls
     
  14. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Heck no. I'm enjoying this as much as you are.

    How about measuring the current through the limit resistor at full bright and as dim as you can get it.

    Also measure the voltage from anode to cathode of each LED in both states.

    Let me know what they are.

    By the way, what time is it there? Don't you ever sleep? :)

    Pkr2
     
  15. would not dimming be the same as taking away voltage? could you not underpower them to begin with and use a250k or 500k (which ever is for volume and tone) as a dimmer switch?
     
  16. I'll get onto those voltages and current tomorrow. I have band practice tonight. ;)

    The time is 3:55 pm, i was on most the day, as in i was downloading some Victor Wooten and kept checking TB every so often.

    Bassist4ever, those values are too high, in a sense they would hit the LEDs with the full 9 volts. Heck i blew one up when i used a 10k pot. Thus the reason for the 2 kohm pot and just for safety the limiting resistor because even the 2kohm causes enough voltage "passed" to make them bright.

    :D:D

    Merls
     

  17. Huh?
     
  18. Nope. It's something I've witnessed with my own eyes. There seems to be a lot of misunderstanding in this thread, so I'm staying out of it. I've had up to 27 LED's dimmed w/ a 5k Ohm pot. The turn on voltage for these is 0.2 volts, with a max voltage of 5V. So when someone says that something that I've done...can't be done. That's pure BS.

    Do what you want, but personally witnessed events are not up for debate. If someone else can't get it to work, then I'm not gonna debate that either.
     
  19. So has the thread been laid to rest??? Maybe we'll just have to agree to disagree. :p

    :D:D

    Merls
     
  20. And with Merls eloquent curtain call, I think that I'll do just that.

    Closed.
     

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