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  1. BobK

    how to discharge battery

    No, at 5Ω it will discharge in 10 hours. Assuming the capacity is correct. Bob
  2. BobK

    Potentiometer only kicks-in in for the last 10% of the turn (guitar effects pedal)

    Did you notice the note that says "linear taper potentiometers?" Bob
  3. BobK

    Why is diode necessary in buck converter?

    No, it there to complete the circuit! Look at the circuit without the diode. When the switch is off, the inductor has one side connected to nothing. How does current flow out of the inductor with no connection to one side? Bob
  4. BobK

    Why is diode necessary in buck converter?

    Draw the circuit with switch open and no diode. Where is the path for the current? Remember, it has to be a closed circuit. Or, think of it this way. What if the inductor is replaced by a battery. Does current flow into the capacitor? Bob
  5. BobK

    Any ideas - Rotary momentary switch?

    Holy Mother of Invention! Bob
  6. BobK

    LED pucks getting hot

    If there is no resistor, then 12V is too high. Mark, can you measure the current drawn when you supply 13V to the puck? Bob
  7. BobK

    DIY Surface Mount Assembly

    It was not. You do not use solder paste for drag soldering, you use wire solder. My description does leave something to be desired. The flux should be applied after tacking down the corner pins. I use a liquid flux pen, putting a goodly amount over the pins and pads. This allows the solder...
  8. BobK

    LED pucks getting hot

    Ripple should not be a problem, since the puck most likely just contains 3 LEDs in series plus a resistor. The problem is too much voltage. Bob
  9. BobK

    DIY Surface Mount Assembly

    You don't feed the solder from the syringe. For parts with only a few leads, you squeeze it out onto the pads, place the part, then just touch each pad with the tip of the soldering iron. For ICs with many pins, you do drag soldering, using regular solder. Basically, you flux all the pins...
  10. BobK

    What can you tell me about paper capacitors?

    Wow, I am picturing the old TVs (B&W) that I picked up by the side of the road to either repair or harvest parts. Harvesting was easier in those days, with point-to-point wiring, just snip them off. Bob
  11. BobK

    LM317 2N3055 Variable Circuit Problems

    Not finished yet, you need knobs! Congratulations. You are now absolved from the requirement to take up knitting. Bob
  12. BobK

    DIY Surface Mount Assembly

    So many questions! I don't know about different grades of solder paste. I doubt that you could use a finer needle. On the syringes that I have used, it is very difficult to squeeze the solder paste out through the needle they come with, making one's hand very sore. You do not need flux...
  13. BobK

    LED pucks getting hot

    Link to the "pucks" that you bought? Bob
  14. BobK

    can't figure what the hell is wrong !

    Here is where you are wrong. Inputs are not low when no voltage is applied. They are floating, which puts them in an undefined state. With TTL, it is actually interpreted as high. With CMOS is could be anything. Since a CMOS input looks like a capacitor, it will often retain it's previous...
  15. BobK

    help with schematic

    Yep, two separate power supplies, but you must disconnect the wire between them. Bob
  16. BobK

    A few questions on electronics

    You have understood nothing I have said. Please go back and read my posts again. Bob
  17. BobK

    A few questions on electronics

    I would suggest a pullup and direct connection to the PIC output port. On startup, set that pin to output and high. When you want to reset, set the pin low, wait for some period, then set it high again. Are you sure you do not want a pulldown instead though? This would disable the shift...
  18. BobK

    Amplifying current in a sine wave

    It is easy to filter to pass sub sonic frequencies. You are trying to filter out the switching frequency, typically 100KHz. Say the the upper end of the passband is 1Hz, this is far simpler than if you had to pass 20KHz. For example, if the 3dB point is 2Hz, 100KHz will be down by 94dB...
  19. BobK

    A few questions on electronics

    2. Try calculating the capacitor that will have 0Ω reactance. You would never need anything near 0Ω. About 1/10 of the input impedance of the next stage at the lowest frequency of interest would be reasonable. 4. You can connect the master clear directly to the micro output, and no pullup is...
  20. BobK

    Amplifying current in a sine wave

    Yes, now that class D amp modules are so cheap, they are the way to go. Bob
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