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  1. BobK

    Base resistor and MOSFET + Rectifier Diode Selection for Solenoid actuation?

    And please learn the correct names of the pins. There is no sink pin on a MOSFET. Perhaps you meant source, which is, of course, the opposite of sink! Gate threshold voltage is typically the voltage that will cause 250 microamps to flow from drain to source. Yes, current flows from the drain...
  2. BobK

    555 timer

    1000 uF and 1.6Meg according to the calculator @HellasTechn posted. Simplest circuit is a 6 or 8 pin microcontroller (PIC10F.) One chip, 1 decoupling capacitor, 1 MOSFET to switch the LED. But of course you need to the tools and the experience to do it this way. Bob
  3. BobK

    I don't understand the meaning/relevance of output impedance.

    Everyone gets this wrong. You do not try to match the output impedance of an amplifier to the impedance of the speaker. There are multiple reasons for this: 1. If the output impedance of the amplifier is matched to the speaker, only half of the available power will go to the speaker, the...
  4. BobK

    Making electrolytic triodes.

    I suspect there is a gain of less than 1. As Steve asked, what is the grid current? Bob
  5. BobK

    Transistor Tyristor x-FET

    No, but under certain conditions, you can use your truck as a replacement for a fence. Bob
  6. BobK

    Electrolytic capacitors: Opinion required please

    Never heard of soldering acid, but, if it is what is in acid core solder, then it should not be used for electronics. Bob
  7. BobK

    Ok To Bridge Left & Right Channels Together?

    Not necessary when connecting two inputs together. And, for the OP: that is not what bridging means. Bob
  8. BobK

    What type of battery is good for emergency power for blackouts?

    A 20000 mAh power bank would power your cell phone for 10 days. You should be able to find a rechargeble flashlight that has a 5V charge port, so the power bank will handle that too. I would look for other devices than can run off such a power bank. These devices are dirt cheap compared to...
  9. BobK

    LED ON / OFF by Magnet

    I happen to be doing this right now! I have made a "music box" with a barbie type doll on top for my dance showcase this year (Viennese Waltz.) I (the gentleman suitor) brings the box, covered with a silk handkerchief to the girl of my dreams (played by the Lovely Wife Morticia, of course)...
  10. BobK

    AC Measurement Question

    It could be that it has an internal capacitor that is shorted. Bob
  11. BobK

    Charging a phone battery

    Will it charge in the damaged phone? Bob
  12. BobK

    AC Measurement Question

    I suggest a measurement error. Are you sure you are not seeing mV instead of V? It is unlikely you would be reading the correct output (DC) voltage with that much ripple. Bob
  13. BobK

    How do I reduce the speed of a 12v childrens car

    The resistance measurement is of no interest. The thing you call a "variable resistor" is not a resistor at all. It is an electronic device that takes two power leads in and outputs a voltage dependent on the position of sliding pieces. That voltage is sent to the motor controller and...
  14. BobK

    El Panel Brighter

    Well, as you have learned, they are not very bright. The are most useful as bacloghing for displays in a dark room. What is your application? Bob
  15. BobK

    El Panel Brighter

    Use an LED panel instead. Bob
  16. BobK

    How do I reduce the speed of a 12v childrens car

    A rheostat for an 1100 Watt motor would be something to see! Bob
  17. BobK

    How do I reduce the speed of a 12v childrens car

    In order of increasing difficulty: 1. Run it from two or one batteries. Simply move the + cable to do that. 2. Mechanically limit the accelerator. 3. Modify the electronic controller. We would need a lot more info for that. A start would be a picture of it. Bob
  18. BobK

    Music playback

    Except he said he did not want a board, wsnts to roll his own. Bob
  19. BobK

    Music playback

    What is the source of the music? It sounds like you are talking about an MP3 player. Bob
  20. BobK

    Countdown Timer with Alarm Trigger

    I am finding it difficult to understand what you are asking for. It sounds like you are saying you push the button, then it waits 15 minutes and then activates an alarm? This does not make a lot of sense, what if help is needed immediately? Or are you saying something different? Bob
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