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  1. BobK

    555 timer and speaker

    The capacitor is to block the DC portion of the signal and allow the speaker cone to move in both directions from its rest position. If your 555 is oscillating, you will get a sound from the speaker either with or without a capacitor, though it may be more distorted without the capacitor...
  2. BobK

    2N2222 NPN Transistor

    The T092 packaged ones are usually designated as PN2222. Bob
  3. BobK

    Unwanted Comparator Offset

    5-6V for a high output is about right, depending on the load on the output. You need a rail-to-rail opamp to get closer to V+. Bob
  4. BobK

    Help with transistors

    Wikipedia would be a good place to start; http://en.wikipedia.org/wiki/Transistor Bob
  5. BobK

    using PORT A of 16f870

    Did you try reading the datasheet? Bob
  6. BobK

    Component questions (transistor, capacitor)

    My bad, I wasn't following the thread and went only by the schematic you posted. Bob
  7. BobK

    Component questions (transistor, capacitor)

    You might have damaged the transistor with that circuit. You need a resistor to limit the current to the base. Bob
  8. BobK

    LED v LIGHT BULB?

    But you need a power supply, heat sink etc. It is still going to cost you close to $10. Bob
  9. BobK

    Mapper

    Yep. The lowest R would light only 1 LED, the highest one all 4. (with the resistors chosen properly). Bob
  10. BobK

    LED v LIGHT BULB?

    Yes. Of course you can by an LED light bulb already built for less than it will cost you to build one. A 60W equivalent uses about 9W, the same as your 3 3W LEDs would and cost about $10. Bob
  11. BobK

    Component questions (transistor, capacitor)

    Show us your circuit. There should be no problem turning off the LED completely with a correct circuit. Bob
  12. BobK

    Mapper

    You would not even need window comparators. You could use a single comparator for each voltage. The number of LEDs that light would tell you which resitor you were looking at. A quad comparator, reisistor and 4 LEDs with resistors would do the trick. Bob
  13. BobK

    RF related queries

    Okay, that is what I was asking. Bob
  14. BobK

    RF related queries

    Did you read this part: When you soldered it to the breadboard did you leave the leads to the capacitor at 18mm? Bob
  15. BobK

    How does this LED driver work?

    Rectified and smoothed a 40V transformer will give you about 55V. You want a 30V transformer, which will give you a little more than 40V. It should be able to give about 250mA for a little overhead, so 30V 7.5VA should work. Bob
  16. BobK

    How does this LED driver work?

    You could build one with an LM317. You woudl need a constant voltage power supply that can supply about 3V higher than needed. Bob
  17. BobK

    How does this LED driver work?

    If you connect that supply to an LED that has a forward current of 180mA, you are going to release the smoke. That supply will give a constant current of 1500mA. You should find one that is either a fixed 180mA constant current supply or one on which you can adjust the current to 180mA. Bob
  18. BobK

    Please Help. How to build this circuit?

    From your description, I have no idea what you are talking about. Bob
  19. BobK

    Instruction set need help

    You really need to go back and learn something about microcontrollers before trying to design one. Bob
  20. BobK

    What does IF stand for?

    In this case, IF means forward current. Bob
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