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  1. BobK

    Turning a USB FM transmitter

    OK, I see. The jack is an AUX input for the transmitter. Bob
  2. BobK

    POT range constraint

    People here are better able to help you if you if you tell us exactly what you circuit is, not something that you think is equivalent. Bob
  3. BobK

    Current regulator

    A 1.2K pot in the LM317 circuit would make it very difficult to adjust the current at the high end (low resistance). If you really need that kind of range of current, I think switching in different resistors (or pots) would be a better idea. Each pot should have a fixed resistor in series so...
  4. BobK

    How long should antenna wire be to receive amateur band?

    What? You can make a radio without a guitar? Bob
  5. BobK

    Turning a USB FM transmitter

    The MP3 player has an audio input and not and audio output? That seems strange. Bob
  6. BobK

    POT range constraint

    Oh, I missed that, I read it as a 50K pot. Are you sure? I have never heard of pot that goes to infinity. What does it measure at half way, infinity / 2? Bob
  7. BobK

    Current regulator

    An adjustable voltage regulator can be wired as a current regulator. See the LM317 datasheet for example. I am not sure about paralleling current sources. Theoretically it should work, but there might be problems. Hopefully someone more knowledgeable will chime in. Bob
  8. BobK

    POT range constraint

    No, I mean 390K in parallel with the pot. 50K || 390K = 44.3K . If you put 45K in parallel with 50K the result would be 23.7K. The equation for resistors in parallel is: 1/R = 1/R1 + 1/R2 Bob
  9. BobK

    POT range constraint

    If you are really only worried about the low end, put a 5K resistor in series, the range is now 5 to 55K. If you really want 5 to 50K, put a 390K resistor in parallel with the pot as well. This will change the taper however to slightly logarithmic. Bob
  10. BobK

    Where buy LED's

    Ebay DealExtreme AllElectronics Mouser DigiKey And many more... Bob
  11. BobK

    How long should antenna wire be to receive amateur band?

    Personally, I would spend the 5 cents. Bob
  12. BobK

    Where buy LED's

    Red LEDs generally have far lower lumens than white or green. This is becuase lumens takes into account how the human eye responds. For a red LED to put out 100 lumens it would have the equivalent power of a green LED at 500 lumens. Bob
  13. BobK

    How long should antenna wire be to receive amateur band?

    Increasing the load does not increase the voltage, it decreases the current. The 100K resistor is there because crystal headphones act like a capacitor and will just charge up to the max voltage seen. The resistor bleeds off this charge and allows them to see the audio signal. Bob
  14. BobK

    Is this true or false

    I did some research on my own, and it seems that some Schottky diodes do work well. The parameter that seems to matter is the Rd or the resistance of the diode at 0V. This is also related to reverse leakage current. Lower on both of these is better. Bob
  15. BobK

    Streaming...?

    Welcome to the forum! I just went through this, so I will give it a crack. I looked up the cable you mention and the Ebay listing has this warning: So, your TV probably does not accept HDMI over VGA. Does you laptop have a VGA connector as well? If so, just connect that to the VGA in...
  16. BobK

    Is this true or false

    I have often wondered about this point, why would Shottky diodes not work in a crystal set? Bob
  17. BobK

    DC Motor Stall Current and Power Supply Questions

    Using a linear regulator for the the 12 supply for the motor and a switching regulator for the 5V supply for the PIC is backwards. The micro will use only a mA or 2, unless there are other things powered at 5V, a 78L05 regulator would be fine. Bob
  18. BobK

    Program from MUC

    PIC microcontrollers and be read unless you explicitly lock them against reading. Bob
  19. BobK

    Can this be done?

    The circuit is in the link I gave you. I don't know how practical it is, or what part to use, but it has only a JFET and a resistor. Try googling to find more info. Bob
  20. BobK

    Calculate the power supply for 10 LED Screen's

    I think you ignoring the fact that the voltage is too high. Bob
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