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  1. BobK

    New project - 1967 oscilloscope restoration

    Very minimalist. Bob
  2. BobK

    PIC A/D

    Are you saying that measuring the voltage at the input you get a full range of 0 to 2.8V, but the ADC is reading a range of 0 to 0.690V? If so, one possibility is that you are not sampling for long enough. Did you go by the recommendations in the datasheet? The capacitor will provide low...
  3. BobK

    Power shutoffs

    Typically, grid tied systems do not supply power when the grid is down. I asked about that when someone came out to evaluate our house for a solar installation of that type. Bob
  4. BobK

    12V to 5V 3A converter

    Younput the resistor across the two outputs of the converter. A 1K will draw only 5mA. The idea is that, perhaps it might stop whining when there is no load. Bob
  5. BobK

    12V to 5V 3A converter

    Put a resistor across the output. Start with 1K, if that doesn’t work, try lower, but watch the power consumption. The power is V^2 / R. pr 25 / R for 5V So a 100 Ohm 1/4 W resistor would be maxed out, so don’t go that low. Bob
  6. BobK

    12V to 5V 3A converter

    It will, on average require less than 3A, but the peak current will be over 3A. A buck converter works by drawing power from the source only part of the time. When it is drawing current, the current will be the same as the output current. Bob
  7. BobK

    Need help for value of resistor

    No, it never becomes a high voltage. The voltage only rises to the level that will allow the current flow, in the case of the diode, that is between about 0.6 and 1V. I don't consider that a high voltage. It if was otherwise, what voltage would it rise to, 100V 1000V, 100 MV? If you scoped...
  8. BobK

    Need help for value of resistor

    The flyback voltage only rises to the voltage that allows the current in the inductor to continue flowing. The flyback diode is forward biased and thus only about 0.6 to 1V, depending on the current and the diode are required to keep the current flowing, and it goes no higher than that. The...
  9. BobK

    Need help for value of resistor

    That should have been diode, not resistor. Bob
  10. BobK

    Assistance in decoding a circuit diagram

    I agree that two of the pins might be connected together. You can determine that using any little circuit, like an led and try connecting one side of the battery through any two connections on the capacitor. Bob
  11. BobK

    1N5822 diodes

    Yes, up to 2 mA at 25C and 20 mA at 100C datasheet Bob
  12. BobK

    Need help for value of resistor

    Because some people think the flyback resistor needs to handle high voltage spikes. In reality, it does not, it only sees the same voltage as is applied to the relay coil. Bob
  13. BobK

    Assistance in decoding a circuit diagram

    Most likely only two of them are connected, the other one is for stability when mounting on a board. It is also a non-polarized capacitor and can be connected either way around. Bob
  14. BobK

    24 Volt DC Transformer to AC mod ?

    The transformer in a 24V DC power supply is probably more like 18AC. That is because you gain a little voltage when you rectify and smooth the AC input to DC. On the other hand, the current capacity should be higher than 1A, because you also lose a bit in current. Bob
  15. BobK

    Question concerning increasing voltage for phone auxiliary speaker

    What @Audioguru means by biasing the LED is that the audio output should be put in series with the battery and a resistor. This means the battery voltage is added to the audio voltage, and that voltage is applied through the resistor to the LED. But you cannot use the same battery for this as...
  16. BobK

    Question concerning increasing voltage for phone auxiliary speaker

    What makes you think that? The OP says he replaced the speaker in an amplified speaker with the LED. The amplifier is being run by the battery, which might well be a 4 cell NiMH which would be 4.8V. The amplifier is either bridged (likely) or not. If it is a bridged class D amp it can...
  17. BobK

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

    You are missing my point entirely. To make the math simpler, lets say your power supply can provide 5A at 20V, which is 100W. And let us say that your heater takes 15A at 5V for 75W. No problem, right, because The heater needs only 75% of the power your power supply can provide? The...
  18. BobK

    P channel MOSFET Current Flow

    Yes. The datasheet for that part indicates a 28 mOhm resistance at -4.5V Vgs. So, with a 20mA LED powered through the drain, the voltage at the drain will be: 5 - 0.028 * 0.02 = 4.9994V And at 1A it will be 4.972V That is why I said it can be considered to be 5V. Bob
  19. BobK

    Function returning pointer

    The syntax is correct, but, as the first reply states, the pointer is invalid as soon as the function exits, thus all you are doing with this code is creating a bug at runtime. To return a pointer that is still good after it is returned either allocate from dynamic memory (malloc) or take the...
  20. BobK

    Convert 24vdc charger into 125vdc charger

    Just out of curiosity, what are you going to charge with a 125V charger? Bob
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