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  1. BobK

    P channel MOSFET Current Flow

    Unless you are approaching the current limit of the MOSFET, the voltage at the drain can be considered to be 5V when the MOSFET is fully turned on. You cannot just connect an LED between 5V and ground, it will likely be destroyed, so, as already stated, you must have a resistor in series with...
  2. BobK

    Need help resistor values

    I have had a bat in the bedroom on two occasions in my house. Quite frightening when you wake up in the middle of the night to discover a bat flying around the room! Actually the lovely wife Morticia was awakened first, and woke me up. I think she attracts them. Bob
  3. BobK

    AC Laptop Adapter -> How to make 19v output into 5v?

    Simply adding a buck converter might not work either. In a buck converter, when the switch is on, the power supply must supply all the current used by the load + some more due to losses. Thus the power supply will need to supply roughly 4 times its max rated current 1/4 of the time. This will...
  4. BobK

    Questions regarding voltage divider for micro controller sensing

    The data sheet will tell you the max output impedance of the divider to get full accuracy. For PICs it is 2.5K for the older ones and 10K for the newer ones. You can also put a capacitor across the lower resistor to lower the effective output impedance to virtually zero. A 100nF would be...
  5. BobK

    Silent electric motor to drive turntable.

    Agree. Getting smooth motion would not be easy, but it is possible. You might need to monitor the back EMF on the non energized coil to determine the optimal switching time. Bob
  6. BobK

    Silent electric motor to drive turntable.

    Yes, you could use a whole series of coils operated simultaneously to get more power. I just showed one pair to make it simple. Bob
  7. BobK

    Looking help to export Eagle PCB to gerber files

    I am sure you can find a tutorial online. As is everything in Eagle, it is way more complicated than it should be. Bob
  8. BobK

    Silent electric motor to drive turntable.

    Here is the basic idea, please excuse my lack of drawing skill. You place neodymium magnet discs around the rim of the turntable, with alternating poles out, N S N S... You arrange two electromagnets, spaced apart half the spacing of the magnets,. To move clockwise: 1. Activate coil A...
  9. BobK

    Silent electric motor to drive turntable.

    I gave you a possible silent solution. Bob
  10. BobK

    Let's talk about memory allocation

    No, I mean what I said in my post. Global variables are allocated at compile time, local variables are allocated when the function containing them is entered during execution. Bob
  11. BobK

    Let's talk about memory allocation

    There are actually 3 classes of memory in a typical compiled program. All are stored in the RAM of the computer. static variable are allocated memory at compile time. These are all variables declared outside of a function and, in C/C++, those marked as static explicitly. local variables of a...
  12. BobK

    Silent electric motor to drive turntable.

    Can you make the turntable itself the motor, by placing alternating pole magnets around it then driving it with a couple coils? I.e. turning it into a stepper. That would be as quiet as the rotating turntable itself. Bob
  13. BobK

    AC Polarity swapping circuit

    That's because he refuses to tell us what he is hoping to accomplish with this. I don't know why anyone is continuing to help. Bob
  14. BobK

    12vDC to 24vac module needs modification

    I doubt that would work. The outputs most likely each switches from high impedance to +12V. That is why a center tapped transformer is used. Bob
  15. BobK

    Restoring ancient digital watch.

    Oh, so spraying it on really means flooding it with solvent, and letting it pour off. Not spraying it like spray paint and letting it dry! That wasn’t clear to me. Bob
  16. BobK

    Restoring ancient digital watch.

    I still don’t see how spraying with a solvent and letting it dry removes any residue. Can someone please explain it? I can see how contact cleaner works on mechanical switches. It softens the residue and then operating the switch brushes it off. But that is not what is being recommended...
  17. BobK

    Restoring ancient digital watch.

    How does that remove anything? Bob
  18. BobK

    connecting two batteries using 2 regs and one panel

    Why not parallel the batteries and use one charge controller? Bob
  19. BobK

    LED Display (Home project)

    If you actually want to duplicate that, and you are very smart, you might be able to learn enough in 5 or 10 years. You realize, or maybe you don’t, that that is basically a video monitor that can be configured to different sizes. I have been doing electronics for over 60 years, and would not...
  20. BobK

    12 v to 48 volt dc boost converter 300 watt

    Why? Will it provide enough capacity? You are much better off using 4 smaller batteries in series. Bob
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