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  1. BobK

    (Woo Woo) Efficient HHO Cell

    Woo Hoo! Get 120 MPG! The technology the car and oil companies are suppressing! And you can make It yourself in your garage! Bob
  2. BobK

    Good Cheap Multimeter

    Yep, no swinging needles or vacuum tubes! Bob
  3. BobK

    Need help with remote firework detonator

    That is a really bad idea since it could be triggered by some other walkie talkie, or interference. Bob
  4. BobK

    need help for power cable : )

    You got it! It was intended as light humor. Bob
  5. BobK

    need help for power cable : )

    A power chord is played on the 3 lowest strings of the guitar. Bob
  6. BobK

    LED Screen

    I presume you will be multiplexing by driving either all of the rows and one column or all of the columns and only one row. You should put a resistor on each row (first case) or the column (second case) that will limit the current to 10 mA. Then you will need a transistor on each column (first...
  7. BobK

    Are PICs still being used

    PICs are still very popular. I use them. Bob
  8. BobK

    4 transistor problem

    Output driver would be the circuit that supplies the voltages to the device. An H-bridge is a driver that can control a bidirectional motor from a single supply voltage. A half-bridge can do that same from a bipolar supply. When I first started out I was very confused by H-bridge thinking it...
  9. BobK

    Voltage converter 120V to 220V

    I guess you like it very quiet. Bob
  10. BobK

    What is this part called?

    When I solder parts this size, using paste solder, I practically tap it with the point of the iron, barely holding it on for any time at all, well under1 second anyway. Bob
  11. BobK

    Phase Shift Oscillator

    As you can see from my different results for 7.5KHz and 750Hz, the phase shift introduced by the opamp is also a consideration, especially as the frequency gets higher. Bob
  12. BobK

    Phase Shift Oscillator

    I have done some simulations with LTSPICE. The result: The sqrt(6) formula is correct. It always overestimates the frequency because a real op amp will add an additional phase shift. sqrt(6) = 2.45. With the given values my simulation comes out to 7558 Hz or 2.37 / 2*pi*R*C. If lower the...
  13. BobK

    4 transistor problem

    Correct. This circuit is called an H-bridge, and it is usually used to allow you to run a DC motor in either direction by reversing the polarity. Bob
  14. BobK

    4 transistor problem

    Both LEDs cannot be on since they are connected to the same nodes with opposite polarity. But, possibly you misquoted the question. If it is which transistors must conduct for EACH LED to be on, consider this: The voltage on the anode must be higher than the voltage on the cathode. Which...
  15. BobK

    Power Supply questions

    18V at 350mA for a toothbrush? That seems excessive. Bob
  16. BobK

    Voltage converter 120V to 220V

    Unless you are using this in a large performance hall, or have the worlds most inefficient speakers, you are likely to damage your ears before your receiver overheats. Bob
  17. BobK

    Please help! Voltage regulator

    What you need is a buck-boost converter. Check on Ebay, there are inexpensive modules available. You cannot control voltage and wattage (power) at the same time. If you fix a voltage, whatever you are powering will decide how much power to draw. A power supply can typically provide a range...
  18. BobK

    Pic and JTAG Programmer

    Seems like a lot of trouble when you can get a supported programmer / in-circuit debugger from Microchip for $35. Bob
  19. BobK

    super capacitor capacity?

    Or, perhaps he did not know that that was all that was needed. That is why I posted. It also gives a good example of how much superior batteries are to supercapacitors in energy / volume density. Bob
  20. BobK

    super capacitor capacity?

    On the other hand, at 38uA average current draw, a CR2032 would operate for about 9 months, so why go to such extremes as supercapacitors and wireless charging? Bob
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