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  1. BobK

    Audio preamp problem

    It is probably not the amp itself, it is probably there on the input. You only didn't hear it before because of the bass cut. What is the input? Bob
  2. BobK

    Audio preamp problem

    What kind of noise 50/60 Hz hum? Bob
  3. BobK

    Stepper Motors. Any Experts?

  4. BobK

    Sweat monitor using electrodes.

    Agree. I was only referring to the test circuit he was using. The noise was higher frequency than the signal in that case, though only by 2X so it would have to be a sharp cutoff filter to do much. Bob
  5. BobK

    On off switch using a DC to DC converter

    That would be an odd chip to use for that purpose. I haven't a clue how one would do so. Bob
  6. BobK

    Sweat monitor using electrodes.

    VF2 is clipping. +-2V in, gain of 5 = +-10V out with a +- 5V supply, not going to work. Also, you want a low pass filter, not a high pass filter to cut out high frequency noise. Bob
  7. BobK

    L7812 Voltage sag with 12V DC motor

    Are you measuring the voltage across the motor, or across the motor + resistor? If you are measuring across the motor, the resistor might be dropping the voltage. If they are 12V fans, you should not need a resistor anyway. Bob
  8. BobK

    Audio preamp problem

    The 1K resistor from the input to V+ looks odd to me. Does anyone know what its purpose is? It certainly lowers the input impedance. Also, negative feedback should raise input imedance no? Bob
  9. BobK

    Can anyone teach me how this H-brige is working??

    The Q1 and Q2 bases will be pulled to ground if input A is high, or pulled to V+ (by the 1K resistor) if input A is low. The value of 1K was chosen to provide enough base current to saturate Q2. Bob
  10. BobK

    LTC4425 chip is insanely small!!!

    Oh, now I remember, I warned you that it would not be easy! The pad makes reflow necessary. Bob
  11. BobK

    LTC4425 chip is insanely small!!!

    Well, I solder chips that small with a soldering iron. Is it a sot-23? And yes, a magnifying glass is essential (at least for me.) I wear one attached to a headband. bob
  12. BobK

    Quick Easy Circuit Question (LED)

    If you want minimum voltage, put the LEDs in parallel, not series. Then a 3V battery is enough (for red or green LEDs.) Use a seperate resistor for each LED. Bob
  13. BobK

    Electronic clock project help

    I doubt that there is a motor that is the smallest and cheapest out there. Here is the smallest: http://www.sciencedaily.com/releases/2011/09/110904140353.htm Here is one that is small and cheap...
  14. BobK

    Sweat monitor using electrodes.

    Horses got fingers? I knew chickens do, becuase they are tasty when deep fried, but horses? bob
  15. BobK

    12 volt to 6 volt with constant current

    I would take a wild guess that it runs at about 3A and then cacluate the resistor: V = I R You need the resistor to drop (12 - 6) = 6V so 6 = 3 R, R = 2 Ohms. The power is V^2 / R so 6 * 6 / 2 = 18 W. Find a 2 Ohm at least 20W resitor or, more likely 2 10W 1 Ohm resistors in...
  16. BobK

    Does this Circuit make sense?

    No, 0.5 is 5 tenth's. See the pattern: 0.005 is 5 thousanths 0.05 is 5 hundeths 0.5 is 5 tenths Bob
  17. BobK

    Ohm's Law or not Ohm's Law... That is the question

    I agree that different people have different ideas about what Ohm's law is, and what components it applies to. Bob
  18. BobK

    single supply opamps

    The major difference between single supply opamps and dual supply opamps is how close the inputs and outputs can go to the power rails. In old dual-supply opamps like the 741 the outputs could typically only get to withing about 2V of the rails, hence the +-15V standard. Opamps called...
  19. BobK

    US apppliance power limits

    Typical wall outlets in the U.S. are either 15A or 20A. I think any appliance with a normal plug is actually limited to 1500W or about 14A. Now if you are talking about an electric stove or dryer that is likely to be the 50A range that G.G. mentioned. Bob
  20. BobK

    Bought a board that has an adjustable pot - how to measure ohm vals

    You're getting ahead of yourself. It would depend on how the pot is connected, which you don't seem to know yet. It is most likely used as a variable resistor (like the LM317) example you showed, and you would only need one resistor. If it is used a a potentiometer, then most likely one...
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