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  1. BobK

    Fluke 89iv funny reading

    I think you are seeing the effect of too much resolution. The meter has more digits than it can accurately display. If you have a meter with 3 digits and it reads 0.00 is that more accurate than a 5 digit meter that read 0.0012? Bob
  2. BobK

    Please help a newbie connect woofer

    What I am saying is illustrated by the circuit you posted. You are calculating the frequency as if the R is 1000Ω. But it is in parallel with the speaker, which is 8Ω, giving you a total resistance of 7.93Ω. The 1K resistor is basically doing nothing in this circuit. And the cutoff frequency...
  3. BobK

    Please help a newbie connect woofer

    You do realize that the resistance in the simple RC or RL filter is the speaker itself, right? Bob
  4. BobK

    Need to draw 5 amps

    There are plenty of high amperage supplies for LED strips available on FleaBay. Bob
  5. BobK

    PSU Using The LM338

    Yep. That will get you only about 10.6V and you need 12 to get 9 out of the regulator. Try hooking it up after the rectifier bridge. Bob
  6. BobK

    Please help a newbie connect woofer

    Have you looked for online calculators for crossovers? I am sure I have seen such a thing before. Bob
  7. BobK

    serial regulator

    So can I. I get approximately 9mA. Here is my math: Voltage at the top of the Zener: 15V. Voltage at the top of the resistor, 24V Voltage across R5 24 - 15 = 9V Current through R5 = 9 / 1000 = 9mA Current into base is negligible, 15mA / beta. Colin, why don't you show us your...
  8. BobK

    Need help with battery power for my project

    A MOSFET will easily handle 2.5A without even needing a heat sink, and probably cost less than a relay. Bob
  9. BobK

    PSU Using The LM338

    A 12V transformer will produce about 15VDC. This is plenty to regulate down to 9V. If you are not getting 9V there is something wrong. Bob
  10. BobK

    Stabilising wienbridge sine wave using FET

    Yes, that is a typical crystal oscillator. There is not difference between "crystal" and "quartz crystal" in this context. A divider consists of using a binary counter, with some logic to reset it after a certain count (an AND gate taking all the bits that make up the divisor and feeding the...
  11. BobK

    PSU Using The LM338

    The heat wasted in a linear regulator is: (Vout - Vin) * Iout If you need only 9V out, using a 24V transformer will produce 5 times the heat of using a 12V transformer. Bob
  12. BobK

    Stepper motor or Servo?

    I must be missing something. Why would you need more than one optical sensor? Bob
  13. BobK

    Piezo element microphone

    "Tiptoe, through the tulips..." Bob
  14. BobK

    Stepper motor or Servo?

    An optical sensor can be either an interrupter type as people have been talking about, or a reflective one. This type sends out light and looks for a reflection. The only thing needed on the wheel then is dark (or light) patches at the index points. I have not used this type, and they might be...
  15. BobK

    Stepper motor or Servo?

    Any method you use that does not involve feedback will get out of sync eventually. Even stepper motors have to be calibrated each time the power comes on. Think of your ink-jet printer, for example. If it is like any I have owned it whirs like crazy when powered up to sync up all the...
  16. BobK

    Headphones mute speakers when plugged in

    You would need a headphone jack with a normally closed switches on the tip and ring. See datasheet here for example: http://www.mouser.com/ds/2/670/sj-356xn-series-519937.pdf Look at the SJ3568N model. You would route the left and right audio thorough the switches to the speakers. When the...
  17. BobK

    Problems with transistor on test circuit (beginner)

    To fully saturate the transistor, you should have a base current of about 1/10th of the collector current. So, if the motor takes 60mA you should have a base current of 6mA. You are driving the base with 3.3V and the base emitter junction will drop about 0.7V, so the voltage across your base...
  18. BobK

    Problems with transistor on test circuit (beginner)

    How much current does the motor draw? The correct connection of the transistor should allow for saturation and a drop of 0.2 to 0.3V. If you are getting more than this, the motor is probably trying to draw more current than the 2N2222 can source, which is about 600mA. Or possibly your power...
  19. BobK

    Solar Panel to charge super capacitor

    To get it to charge to more than 22V you will need a boost converter. Bob
  20. BobK

    Stabilising wienbridge sine wave using FET

    A square save at 50KHz and peak voltage P actually has more energy at 40KHz than a sine wave with the same peak voltage. In fact, the 50KHz sine component of the Fourier transform has 4/pi times the amplitude of the square wave! See here...
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