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  1. BobK

    How do I add specific sound to my project.

    An MP3 player. There are plenty of cheap boards out there, some of which are set up to control electronically rather than by pushbutton. Bob
  2. BobK

    Just a quick check of my circuit

    You don't need all of those diodes. If you make the column drivers toggle between input and output driven low, and use the internal pull-up on each row input. You scan by making all the columns inputs, then you make one column an output at a time and read the row inputs for that column. Bob
  3. BobK

    Pulse swwitching and circuits

    About 2 weeks if I order PCBs from China. Bob
  4. BobK

    2 layer and 4 layer pcb

    That's huge. Would not work well with the 0.65 mm pitch PICs I am using now! For DIP work, I typically use 15 mils (about 0.4 mm), and I go down to 12 or 10 mils to sneak lines between pins on a DIP. And, of course, wider if more than a few hundred mA of current. M
  5. BobK

    Accuracy Component Tester.

    Um... A 0.1Ω resistor read as 0.11Ω is off by 10%. To be 1% it would have to be between 0.099 and 0.101. The error has to be calculated as a percentage of the correct value. Bob
  6. BobK

    Hi folks! I'm new here and don't understand JFETs

    OMG, I was in Okinawa in 1958! I don't remember an earthquake though, I was 6, and my dad was there as a CIA employee. We left in May of that year, so I might have missed the quake. Bob
  7. BobK

    Hi folks! I'm new here and don't understand JFETs

    Well, if you want flat response down to 20 Hz, what corner frequency would you use? Clearly not 20 Hz, since it would be down 3 dB at 20 Hz. Bob
  8. BobK

    Hi folks! I'm new here and don't understand JFETs

    My mistake, I had typed 500 instead of 1500 into the calculator. You are right, the cutoff is 4.8Hz. Bob
  9. BobK

    Hi folks! I'm new here and don't understand JFETs

    Wasn't expecting tubes! But the circuit is the same as that used with a transistor. The emitter or cathode resistor sets the gain to roughly it's ratio to the load resistor. The capacitor passes all frequencies above it's cutoff around the resistor giving you a higher gain, limited only by...
  10. BobK

    Hi folks! I'm new here and don't understand JFETs

    First, we need a schematic. Not all audio preamps are identical. If you are talking about the resistor from the emitter to ground, the capacitor is doing just the opposite of what you think. It is allowing audio frequencies bypass the resistor so that the full gain of the transistor is seen...
  11. BobK

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

    Lower it further to 0 Ohms and you can transfer 1 Watt. The maximum power transfer theorem tells you what load impedance will allow the transfer the max power for a given source impedance. For a given load impedance, it is much simpler: The source impedance to transfer maximum power is zero. Bob
  12. BobK

    How to wire up an Atmega32u4

    Look at the circuit for an Arduino board that does that. Bob
  13. BobK

    TTP223 Touch Sensor with LED Strip

    This line from the OP implies that he is using 2 power supplies with the 12V version, presumable 12V and 5V. Bob
  14. BobK

    Led electronic clock kit

    Congratulations. Bob
  15. BobK

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

    Yep, for exactly the same reason as a linear regulator wastes power and a switching regulator does not. In fact, an class AB audio amplifier is a linear regulator that follows an input voltage and a class D amp is a switching regulator that follows an input. Bob
  16. BobK

    TTP223 Touch Sensor with LED Strip

    With a floating gate? Yes, that can happen. In fact, it will likely be sensitive to touch! Bob
  17. BobK

    Can 1 Raspberry Pi 2 Run Two Arduino Mega using USB?

    A USB port can deliver 500 mA. Unless you are powering other devices, an Arduino should use nowhere near that. Calculate how much current the Arduino and whatever is connected to it use, and you will have your answer. Bob
  18. BobK

    Motor controller ic

    Have you tried reading the datasheet? Bob
  19. BobK

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

    Which made sense because the output impedance of the amp was much higher than the impedance of the speaker. In that case, the power transfer would be limited to a fraction of the available power. The ideal case is zero output impedance, which we are closer to today. With zero output impedance...
  20. BobK

    Making electrolytic triodes.

    It is unlikely with a current gain I calculate as 18 / 350 or 0.05 Bob
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