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  1. BobK

    LED's to use with speakers

    P = I * I * R 50 = I * I * 4 12.5 = I * I 3.54 = I Vrms = I * R V = 3.54 * 4 = 14.2 Vpeak = Vrms * sqrt(2) = 14.2 * 1.414 = 20V So the max voltage peak will be 20V. Now, what is the drop across the LED? Assume 2.5 so: V = I R 20 - 2.5 = 0.02 R 875 = R This will be the...
  2. BobK

    correct resistor help

    Hopefully, the calculator also told you that the resistor will dissapate 8 Watts. It's going to get hot, and if you use less than a 10W resistor, it's going to melt. Bob
  3. BobK

    comparator hysterisis

    From the third equation: 1 = (12 - 0) * (R1 / (R1 + Rf) (R1 / (R1 + Rf) = 1 / 12 (and thus Rf = 11 * R1) Then plug the 1/12 into the other two equations and you get: Vl = 4.675 Vh = 5.675 So, pretty close to what you measure, allowing for the resistors to be off a...
  4. BobK

    need advice with speakers+LEDs

    I guess that depends on whether you want the LED's brightness to follow the level of the music or not. bob
  5. BobK

    Combining two audio sources into one set of headphones

    If each of the signals is strong enough that you would never turn it up all the way, you can do it by simply putting a resistor in series with each and connecting the two together to go to the headphones. The resistor should match the impedance of the headphones. Typical headphone impedance is...
  6. BobK

    Circuit maker program?

    LTSPICE from Linear Techonologies has a very easy to use schematic capture program, is completely free, and you can simulate the circuit after you draw it! Bob
  7. BobK

    run a low voltage led(3volt) at higher voltage(12-18 volt)

    I hope you plan on having a massive heat sink if you run this LED at 3A. Bob
  8. BobK

    pic 16f84

    The address of the STATUS register is duplicated in both banks so that you do not have to do a bank select before referencing it. Any reference to either address goes to the same physical register. Bob
  9. BobK

    RGB Power LED with true red

    I have bought two different 3W RGB LEDs, and on both the "red" is decidedly orange to the eye. One is from Kingbright and it's dominant red wavelength is listed as 625nm, which they call reddish orange. I have looked and looked and cannot find any the have a red wavelength any higher than...
  10. BobK

    Simple Traffic light control

    This sounds like a great first microcontroller project. You need 4 outputs and one input, so an 8-pin PIC like PIC12F629 would do fine. You would save a lot of parts compared to trying to do this with '555s. Bob
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