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  1. BobK

    Identifying Positive, Negative of LED unit

    What DO you know about the LED? Forward voltage, operating current? Bob
  2. BobK

    Help using TIP42c

    It is not a good idea to parallel BJTs, their characteristics will differ enough that one will carry most of the current, heating it up, which causes it to carry even more of the current (thermal runaway). Bob
  3. BobK

    Quad Comparator Help

    And, you will need a transistor switch to turn the siren on and off. The comparator cannot do this alone. Bob
  4. BobK

    Questions about MOSFETs

    If a MOSFET is used in an audio amp output stage, it is probably a class D amplier. A class D amplifier does amplify audio by swithing only fully on or fully off. It does this by using PWM. I.e. the percetange of time the switch is on corresponds to the voltage of the signal being amplified...
  5. BobK

    Help using TIP42c

    Yes. 680 between the uController and the base of the 2N2222, then 25 Ohm between the collector of the 2N2222 and the base of the TIP42C. And a heat sink on the TIP42C. You will probably melt if if you try to run 6 Amps without a heat sink. Bob
  6. BobK

    Potmeter help

    Well, that will give you 0 to 11.1V. You need an additional resistor betwen the upper connection to the pot and the 11.1V supply Rpot / (Rpot + Rfixed) = 5 / 11.1 For example: If the pot is 10K, the fixed resistor would be 12.2K. Bob
  7. BobK

    Demodulation

    I think you need an electric guitar to do that :) Bob
  8. BobK

    LED Flasher Relay Flash Rate

    The only change needed to make it run at 12V is the current limiting resistor for the LED. This really needs to be changed anyway, since you will not likely use exactly the same LEDs that it was designed for. If you need help, I will monitor this thread. You can also change the flash rate...
  9. BobK

    Help with actuator project.

    A power window actuator from a junkyard would be a possible device that would have the kind of travel you need. Bob
  10. BobK

    Need an advice. Have idea to create simple computer , with punched card programming

    I agree with Kris. Using and FPGA will give you the same learning of the computer at gate level without the drudgery of having to build it phyiscally. In fact, this idea has been percolating in the back of my mind for a project once I reach retirement and have the time. FPGA deleveopment...
  11. BobK

    Why did my PA fuse blow?

    Time to use that dim light bulb trick. Bob
  12. BobK

    How do i use a 20a 12v toggle switch where once was a 10a 250v rocker switch

    Did it occur to you that there might be a reason that the original switch was rated at 250V? Bob
  13. BobK

    Compression by the resistor

    Kris's post has a lot of good info. I think if you want to build a synthesizer you should look into op amp circuits. They are much easier to design with and much more well behaved than the circuit you are using. For example, you would not have the output impedance problem with op amps, they...
  14. BobK

    Guitar Amp Modification

    Tuner, here, means that is used to tune musical instruments. So not a misnomer. Bob
  15. BobK

    Help using TIP42c

    No, you would have to use a 25 Ohm on the tip42c to get 6 amps. If you switch to a P channel MOSFET, it will not help for it to be logic level since it's gate is referenced from the + supply and you will need a level shifter anyway I have actually never heard of a P channel logic-level...
  16. BobK

    Compression by the resistor

    Where in your circuit are you taking the output from? What frequency is it oscillating at? On and AC setting I would expect the low peaks to go up and the high peaks to go down, i.e. toward 0 volts. If the scope is on DC I would expect both to go towards zero as well, which would be down...
  17. BobK

    why are these transistors getting so hot?!

    If the amp is working normally, it is likely normal. Bob
  18. BobK

    Compression by the resistor

    You need two resistors wired as a voltage divider. Use a 10K to the output, a 1K to ground, and take your output from the junction of the two. Votage divider Bob
  19. BobK

    why are these transistors getting so hot?!

    It does seem strange though that the voltage regulators would get that much hotter than the output transistors. Bob
  20. BobK

    LED Flasher Relay Flash Rate

    Got it! Bob
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