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  1. BobK

    Simple Overvoltage protection

    Look up "crowbar circuit" Bob
  2. BobK

    Why is this LED not 20 Watts?

    Would somebody please close this thread unless the thread starter will give us the specs of the LED he is using so that we can reccommend a proper driver? Bob
  3. BobK

    Need help with a simple circuit

    Most parts are purchased online now (like everything else.) Bob
  4. BobK

    How to wire this LED display?

    I am going to guess that it is either a common cathode or common anode display wired as follows; 1 pin for each of the 7 segments 1 pin for common (anode or cathode) of each digit 1 pin for the two colons Take a 9V battery. Connect a 1K resistor to the +. You now have two leads, the other...
  5. BobK

    Can anyone recommend a simple linear VCO?

    Just out of curiosity, how did you get the control voltage to be accurate to within 0.06%? I am quite expeienced and I cannot imagine how to do it in a way that it would not drift more than that. Bob
  6. BobK

    NPN Transistor Amp not working!!?!?!

    Please show us a schematic of your "working" circuit. Bob
  7. BobK

    Creating a Moisture percentage detector for soil

    The circuit you need is an analog to digital converter. Look it up. I agree with Alec that I would use a microcontroller with a built int A/D converter to this since it an handle both the conversion and the driving of the LED display with a single chip. Bob
  8. BobK

    NPN Transistor Amp not working!!?!?!

    Seriously? Can you show us? Bob
  9. BobK

    Can anyone recommend a simple linear VCO?

    I don't understand the use of the word "so" in this sentence. Why does that fact that "it is for audio" imply that the linearity should be better than 0,059%? And, if indeed you need that kind of accuracy, you are talking about a lab precision instrument here. What is it you are trying to do...
  10. BobK

    I want to made a mini heater for a my 36.8v 8.62A 320w solar panel

    Heater. By the way. You would get more heat by using a solar water heater than using photovoltaic cells to power an electric heater, and for less money. Bob
  11. BobK

    Why is this LED not 20 Watts?

    What are the specs of the LED you are using? Voltage and current? You could probably get close to 20W of output by putting 2 of them in series and driving them with the driver you have. Bob
  12. BobK

    NPN Transistor Amp not working!!?!?!

    And even with the circuit 73'd de Ed posted, you will get about 1/4 W of audio output. Enough to make sound from the speaker that won't wake someone one in the next room. Bob
  13. BobK

    Convert FM wireless headphones to Bluetooth?

    You can buy a bluetooth audio receiver module. Just replace everything inside the headphones with the BT module, connecting it's outputs to the headphones. Bob
  14. BobK

    741 circuit amp wont turn on

    No, this will never work, even without the capacitors. The input pins cannot source or sink current, and that is what your circuit is expecting. How about telling us what you are trying to do. I cannot determine that from the totally flawed schematic that you posted. Bob
  15. BobK

    Op Amp 741

    What is the signal generator? It probably already has drive capability at least as good as your 741. Bob
  16. BobK

    Difference in battery capacity between Alkaline and NiMH cells

    According to the chart: https://en.wikipedia.org/wiki/D_battery An NiMH D battery can be up to 12000 mAH And take note of this sentence in the same article: Bob
  17. BobK

    MOSFET and Switching power loss for H Bridge motor driver

    dI / dt = V/L With 5V and 0.15H dI / dt = 5 / 0.15 = 33V per second At 800Hz 50% you have 625 usec to build the current in each half cycle. So the current should reach: 33 * 0.000625 = 20mA At 30 Hz you have 1/60th of a second or 17msec so the current can reach, ignoring the resistance...
  18. BobK

    Parallel and series generator and batteries

    But your diagram is showing two 6V batteries in series giving 12V. And a 12V generator attached directly to 6V battery. Not good. To elucidate Steves point a bit. You have two generators, each capable of 12V and 6A. And you want out 24V and 12A. The output is exactly twice the power of the...
  19. BobK

    MOSFET and Switching power loss for H Bridge motor driver

    I can't believe I missed that. Bob
  20. BobK

    MOSFET and Switching power loss for H Bridge motor driver

    At that kind of current there should be no significant drop by a MOSFET driver. You should get an average current that is very close to the current at 5V multiplied by the PWM duty cycle. Bob
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