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  1. BobK

    help please

    Yes, and what does that say about the lowest frequency it will reproduce? Bob
  2. BobK

    tip120 driving led array

    This is why I wanted to see a circuit. 1. Most beginners connect the load to the emitter of an NPN transistor, as you have. This makes an emitter follower, where the emitter is at a voltage of about 0.6 (or 1.2 for a darlington) less than the voltage driving the base. When you put the load...
  3. BobK

    tip120 driving led array

    First things first, show us your cicuit. We cannot devine how you connected it. Bob
  4. BobK

    Now I am going to ask 3 stupid questions, please dont laugh. but i cant seem to find info

    Yes, it works like a standard transformer. If you had a variac that was actually drawing 10A in the primary with it set to 12V output, there would be 100A in the secondary. However, that would be a massive piece of equipment. If you think about the power, it cannot be otherwise. You cannot...
  5. BobK

    Now I am going to ask 3 stupid questions, please dont laugh. but i cant seem to find info

    Did you actually read the answers? About the amps: I told you that if there was 120V 1A in the primary, there must be 12V 10A in the secondary. And you ask if the amps goes down. No, going from 1A to 10A is not going down. About the minimum voltage: Two of us answered that it would work at...
  6. BobK

    Woo-Woo The Engineer's Ghost Box

    In the field of electrical engineering, what you are calling ghosts is what we call noise. We have to deal with it our circuits. We add extra circuitry, are we are careful about how we wire things in order to minimize it's effect. Bob
  7. BobK

    Woo-Woo The Engineer's Ghost Box

    "I can't explain why this device triggers unexpectedly, therefore it is ghosts doing it." This is the logical fallacy called argument from ignorance. Not knowing something does not imply anything. The device is triggering because it is set to be right on the edge of triggering and there is...
  8. BobK

    Darlington Pair's Current Direction

    No, it is from the base to the collector. Your 10Ω base resistor is ridiculously low, and this circuit is not operating the way a darlington normally would, it is operating like 2 diodes. There is plenty of current to saturate Q2, so it's collector will be at about 0.2V. This make a current...
  9. BobK

    Now I am going to ask 3 stupid questions, please dont laugh. but i cant seem to find info

    1. A variac is a kind of transformer. The rule for transformers is that power in = power out. So, if the primary of a variac is drawing 1A at 120V, that is 120W. The secondary, to have equal power, must be 120 / 12 or 10A. There are, of course, some losses due to heating, so the input power...
  10. BobK

    Homemade capacitors, that hold a charge?

    Yep, you got me there. Ob
  11. BobK

    Homemade capacitors, that hold a charge?

    Hi Sally Pressure on a piezoelectric crystal causes charge to migrate to it's surface, much like a capacitor. If you put a weight on a crystal it will develop a voltage based on that charge. If you draw current from it, the charge dissipates and the voltage is reduced, just like a capacitor...
  12. BobK

    Beginner needing help - Simple timer circuit for reversing 5v motor

    Do all of these motors need to operate synchously. If so, it is much more complicated. Bob
  13. BobK

    Homemade capacitors, that hold a charge?

    That is not a Piezo electric effect. That is the result of the capacitance changing when the plates are pushed closer together. Be excited though, you have just discovered how an electret microphone works! Bob
  14. BobK

    Board design help! Some buttons and led on a perfboard

    So, I would say 3 hours for me to make PCB that size and complexity. Though I am moving towards SMT, which is faster due to much less drilling. Bob
  15. BobK

    Board design help! Some buttons and led on a perfboard

    Audioguru, About how long would it take you to design and make the board shown in post #6? Just wanted to compare to what it would take me to do a PCB at that level of complexity. Bob
  16. BobK

    Input lower than set output for LM2576

    The inductor core may be saturated, but it would not matter if it is not switching. Bob
  17. BobK

    Trumps solar wall, forget politics we should just build the thing

    In the US. Doesn't my flag show up? Bob
  18. BobK

    Trumps solar wall, forget politics we should just build the thing

    You do realize that illegals do not get welfare, right?, nor food stamps, nor medicare, medicaid or social security. https://www.nilc.org/issues/economic-support/overview-immeligfedprograms/ In fact, since 1996, even legal immigrants are not eligible for most benefits for 5 years. Bob
  19. BobK

    Trumps solar wall, forget politics we should just build the thing

    Seeing as I live in such a country, I agree wholeheartedly. Bob
  20. BobK

    Trumps solar wall, forget politics we should just build the thing

    I did not say we should not try to keep illegals out. I said that the physical border wall won't do it. The government (and this covers past administrations as well) is much more concerned with making people think they are doing something to solve a problem than they are with actually solving...
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