Color Organ design

Discussion in 'General Electronics Chat' started by nabby, Jun 7, 2012.

  1. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    Could you expand on that?

    I'm here because this is the same project I'm about to start working on, and I know enough to know things are missing, but not enough to know exactly what to use or where to put them. I'm working from an 8.5v source to a TIP31C hooked to a sound line to turn the transistor on and off, and using 3V - 3.4V LEDs @ 24mA max continuous / 75mA max peak, two in sequence with a 1/4W 100ohm resistor to keep the current somewhere between 17 and 25mA (depending on voltage).

    I used a couple of online LED calculators to figure out the number of LEDS and what resistor to use. I assume I need a resistor in the line between the stereo input and the transistor, but I don't know how much because data sheets overwhelm me.

    I'm also not sure where to put the protection diode. Is it between the 8.5V and the first LED, between the last LED and the transistor, or between the transistor and ground, or does it even matter at all and it stops reverse voltage across the circuit? Does the size/type of diode matter, or will it allow (nearly) zero voltage/current one way and as much as I need the other? The LEDs have a reverse current of <=30uA and reverse voltage of 5~6V.

    If I can draw up a better version of this circuit, perhaps I can start spreading the info around to more amateurs to do it right the first time.
     
    Last edited: Jun 7, 2012
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I don't know the output voltage and current from your "sound line".
    If it is from the output of a power amplifier then a resistor must be added in series with the base of the transistor to limit its base current (or the base-emitter of the transistor and/or the output of the amplifier will burn out due to too much current). The base current must be 1/10th the collector current. Calculate the resistor value to limit the base current to 2.4mA.
    The absolute maximum reverse emitter-base voltage is listed on its datasheet as only 5V which most power amplifiers exceed so a small diode (1N914 or 1N4148) should be connected from the base (diode's cathode) to emitter (diode's anode).
    If your "sound line" is only line level then it does not have enough voltage or current to turn on the transistor.

    Correct.

    As I explained above, the resistor value is simply calculated using basic arithmatic and Ohm's Law. You must know the minimum and maximum power of the amplifier into an 8 ohm speaker to find its output level.
     
  3. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    I've seen a lot of people around the internet making this device using a headphone jack as inputs, or wiring into a pc sound card, or something similar with great results. Is this line level, or does it count as an amplified source? I was kinda hoping there was a standard for RCA lines between an electronics device and a TV, which I could tap into (this is for in my home, not my car).

    I'm sorry for this silly question, but I don't quite understand how this works. I put a diode between the base (connection from stereo) and the emitter (connection to ground) and this stops reverse voltage from the main power loop from going up the line to the base? If so, how?
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
    759
    Can 10 year olds sell components on the net.

    Who is making those circuits. They should know that it is not the way to wire a transistor with leds not to mention the missing base resistor.

    Why in God's name do they put schema's like that ****.

    Is it to attract n00bs and make money
     
  5. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    Yes, probably. But on the plus side, here I am, a noob, and because of this crappy design, I'm here trying to learn how to do it right. I really like the concept of making a couple LEDs blink with an audio input, and from what I've seen, this design works, even if it's not designed well. So I'm hoping that with some tweaking, I can redesign it to do the same thing, but in a more proper way. Is there a better way to use input from an audio line to make LEDs blink?
    The result is pretty impressive, just watch the vid over on http://hacknmod.com/hack/led-light-box-thumps-to-your-music/ where I first read about the design.
     
  6. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    This guy made a really nice looking one but said to add a 1K resistor between the audio wire and the emitter. http://youtu.be/poUqSbmd0Ms

    Now maybe I'm misunderstanding transistors, but doesn't the audio signal need to attach to the BASE leg to turn the transistor on and off, and the COLLECTOR/EMITTER legs are used to complete the circuit with the full power supply and all the lights? Maybe what he said was a typo.
     
  7. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    More of the same, this guy put this in a game console and wired the audio lines into the audio pin-outs of the motherboard which I assume are line-level.

    [​IMG]
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A transistor needs 0.6V between its base and emitter to begin to turn on and it needs up to 1V to completely turn on. Line level for consumer products is 150mV to 250mV RMS which is 0.35V peak on the loudest parts. Then the transistor will never turn on. Headphone outputs deliver up to 50mW RMS into 32 ohms which is 1.8V peak on the loudest parts which can easily turn on a transistor.

    But most of these Hacks or Instructables connect the base and emitter of the transistor directly to the output of a power amplifier (usually one that drives a sub-woofer speaker). Its output might be only 10W RMS into 8 ohms which is 12.6V peak for the loudest parts. A higher power amplifier has a higher outputr voltage. My stereo produces 75W RMS into 8 ohms which is 34.6V peak for the loudest parts.

    The transistor base-emitter is a diode. It begins to turn on when the voltage is 0.6V and with 1V then its base-emitter current is maybe as high as 1A. If the voltage is higher then the current is much higher. The current might be 10A when the voltage is only 1.5V. 10A will blow up the transistor and/or blow up the amplifier so a resistor must be used in series with the base to limit the current.

    The absolute maximum emitter-base reverse voltage of the transistor is 5V. The audio signal is AC so half is positive and the other half is negative. If the negative peak exceeds 5V then the transistor emitter-base has "avalanche breakdown" which causes the transistor to slowly be destroyed if the current is limited with a series base resistor.


    The connection from the stereo goes to the series base resistor to limit the current. The base-emitter conducts like a diode when the AC signal swings positive and the diode conducts when the AC signal swings negative. The maximum voltage across the conducting diode is only 0.6V to 1V so the emitter-base of the transistor is protected from a higher voltage.

    The video is a fake because it shows 6 blue LEDs but the schematic shows only 4 blue LEDs. Another video shows many LED connected directly in parallel like light bulbs. LEDs should NEVER be connected directly in parallel.

    This entire circuit is a fake because a blue LED usually needs 3.5V then four in series need 14V and will not light when the battery as shown is only 12V.
     
  9. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    So if the circuit is fake, my question is, would there be a fairly simple real circuit I could build to do this using a few cheap parts? I don't have a lot of space to work in, so I don't want to use a board, just some components wired together.
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    1) What is the peak voltage of your "sound line"?
    2) How many LEDs and what colour are they (the colour determines how many volts they need)?
    3) Ordinary 20mA LEDs or higher power LEDs?
     
  11. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    Well I'm doing this to a friend's game console for him as a way for me to learn more about electronics. My sound lines are going to be from pins on the motherboard that connect to it's A/V plug which turns into red/white/yellow RCA plugs for the TV, and I would like to assume it's running at line level, but I can break out the multi-meter and run some tests if need be.

    The exact details on the LEDs are such:
    3mm Blue 5,000MCD 3.0-3.4v / 24mA
    Reverse Current (uA) : <=30
    Life Rating : 100,000 Hours
    Viewing Angle : 120~140 Degree
    Absolute Maximum Ratings (Ta=25°C)
    Max Power Dissipation : 80mw
    Max Continuous Forward Current : 24mA
    Max Peak Forward Current : 75mA
    Reverse Voltage : 5~6V
    Lead Soldering Temperature : 240°C (<5Sec)
    Operating Temperature Range : -25°C ~ +85°C
    Preservative Temperature Range : -30°C ~ +100°

    I ordered 20 of them, but I was planning to do 2 per channel with a 100 ohm resistor, because the power wire to the unit has a sticker that says 8.5V --- 5.65A and I'm going to tap into the positive and ground points where it connects to the board. But isn't it possible to run multiple strings of LEDS in parallel as long as each one is 2 LEDs and a resistor? I'd really like to be able to get 4 LEDs per channel if possible.
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    With a supply that is 8.5V and two 3.0V LEDs in series then a 100 ohm current-limiting resistor causes a current of (8.5V - 6.0V)/100= 25mA which is too high for your little LEDs. use 120 ohms then the current will be 21mA if the LEDs are both 3.0V. If the LEDs are both 3.4V then the 120 ohm resistor will cause a current of 14mA which will be fine and will not be dimmed much.
    Your power supply has a lot of current so it can power hundreds of LEDs.
    Each string of two LEDs and a 120 ohm resistor draws 14mA to 21mA so many strings can be used if the signal source has enough current for the base of the transistor.
    You want only ten strings so the maximum total LED current is 210mA then the base current should be 21mA which is too high for a line-level signal but is fine for a headphones output signal.

    If you connect four 3.4V LEDs in series then you need a power supply that is about 16V with a 180 ohm current-limiting resistor.
     
  13. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    Oh, when I saw the info on the LEDs that said max peak was 75mA, I thought that meant it could handle current above that 24mA as long as anything higher wasn't constant, which it's not if it's going to be just turning on and off.

    Here in a little bit I'll see if I can take those multi-meter readings, but I was told that they are line level and need amplified. A few people have talked about using an audio amplifier like LM386 to increase the signal, would this work?
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The peak current for an LED is for only a moment. The duration is very short so that it does not melt. Usually the recommended continuous current for a 3mm or 5mm LED is spec'd at 20mA.

    The 5mm Name Brand (not E-bay Chinese) Fairchild LEDs I use have an absolute maximum continuous current of 40mA, a recommended continuous current of 20mA where all characteristics are spec'd and a peak maximum momentary current of 200mA at 1kHz 10% duty factor (on time is 0.1ms and off time is 1ms).

    Most multimeters cannot measure frequencies above 60Hz accurately.

    What is the signal that you want to amplify?
     
  15. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    You mean what frequency in the waveform? Ideally, I'd like to use the line level signal from the audio pin-outs and have any sound of around 90Hz that's at least half way between zero and maximum volume produce enough current to "turn on" the transistor and allow the 8.5V to hit the LEDs. But I'm willing to bend a little on this if necessary for the sake of simplicity.
     
  16. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Consumer line-level signals have a peak voltage that is too low to turn on a transistor. Then the LEDs will not light.

    You need to make a preamp that boosts the signal level or use the already amplified headphones output.

    LEDs are not "hit" with 8.5V. Instead they are turned on with about 20mA of current, not voltage. The voltage must be high enough for the series resistor to create the 20mA of current according to Ohm's Law.
     
  17. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    The preamp is what I was going for. Isn't that what the LM386 does? How complicated is it to build a preamp?
     
  18. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    An LM386 is a small power amplifier (not an opamp and not a preamp since the transistor is not needed) that can drive about 18 single LEDs, 36 2 LEDs in series or 54 3 LEDs in series.
     
  19. nabby

    Thread Starter New Member

    Jun 7, 2012
    23
    0
    Alright, I wanted to make sure this is a line-level source because I've been talking to a guy who has shown me a few vids of his xbox 360 with this same crappy circuit in it and he seemed to get a bit pissy when I suggested that it shouldn't work. There's a guy over there who tried to explain why this does work. He said the TIP31 is a bipolar junction transistor and is current biased, not voltage controlled. Does this make any sense? Cuz I'm lost.

    I tested with my multimeter where the power line enters the unit and it's running 8.72V not the 8.5V it says on the sticker. It's not a very good power cord and I have a new one on the way, I'll test it out when it gets here. I found a place on the board that according to my multimeter gives off 3.42V. I was pointed to these two spots by other modders who used them for always-on LEDs. If I wired a single LED to that point, would I need a resistor at all or would that extra .02v still hurt the LED?
     
    Last edited: Jun 9, 2012
  20. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I have never measured the output of an Xbox 360.

    Yes, the input to a transistor is a current. Its voltage is a little more than 0.6V. At 1V the current is high and at 1.5V the current is extremely high so the current must be limited with a series resistor.

    Light bulbs are simply an accurate resistor. Light bulbs (with the same part numbers) are exactly the same. Light bulbs are fed a voltage since each one will use exactly the same current.

    LEDs are diodes and each one has a different voltage requirement because they cannot make them exactly the same.
    If you connect an LED that needs 3.0V to a voltage that is 3.42V then its current will be too high and the LED will burn out soon. If you connect an LED that needs 3.6V to a voltage that is 3.42V then it will be dim and its brightness will change a little when the temperature changes.
     
Loading...