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  1. BobK

    Power for Multiple DC Motors

    If those are bipolar transistors you need a resistor between the Arduino and the base. Bob
  2. BobK

    Blowing a 3A fuse with an AA battery?

    I risked it and I get 6A from an AA cell. Bob
  3. BobK

    Best Speaker To Use As Microphone

    Whoa. That possibility had not even occurred to me. Bob
  4. BobK

    Laser dalek!!

    Using an NPN transistor: - wire from Dalek to - wire of laser battery + wire from Dalek to resistor to base of transistor + wire of laser to + of battery - wire of laser to collector of transistor emitter of transistor to - wire of laser battery Bob
  5. BobK

    Laser dalek!!

    We have a resource for that: https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/ Bob
  6. BobK

    Best Speaker To Use As Microphone

    http://users.firstva.com/hale/Infrasound.html Have fun. Bob
  7. BobK

    Battery charging and output voltage regulating please help

    There are no 12V Lithium cells, so, most likely each battery will have to be 4 cells in series, giving you a nominal 14.7V. You would need a very complex charging system to charge these in place. Bob
  8. BobK

    Laser dalek!!

    Much easier to jus use a transistor as a switch. Are you sure about your the 0.01mA reading? That sounds very wrong as well. How did you measure this, with the laser in the circuit, I hope? Bob
  9. BobK

    Heated Mirror

    Okay. That does not mean that your heater is pulling 4A. You need to put an ammeter in series with the power supply to determine how much current is actually being used. For all we know, there is an open circuit somewhere and there is no current being drawn, or there is a short and the power...
  10. BobK

    Designing an iPhone speaker dock.

    That is an opamp. It is not capable of driving a speaker. You need an audio power amplifier. Something like this should work well...
  11. BobK

    Heated Mirror

    That is 60W, which should produce quite a bit of heat (ever touch a 60W light bulb that is on?) When you say "applying 15 Volts at 4 Amps" do you mean connecting the output of a power supply rated at 15V 4A, or do you mean you have actually measured the voltage and current at 15V and 4 Amps...
  12. BobK

    RC-filter for electret mic and USB sound card

    The circuit above is the way the mic is normally used, with R2 begin the input impedance of the amplifier it is feeding. Simply reducing C1 would get you a high pass effect. Bob
  13. BobK

    Best Speaker To Use As Microphone

    Yes, that is why the recording industry uses speakers to make those wonderful recordings we all listen to. Bob
  14. BobK

    If the source voltage is the same as LED voltage, is a resistor necessary?

    The resistor actually acts a negative feedback. If the current goes above the design current, the resistor will drop more voltage at the higher current lowering the voltage across the LED, which is how the current is limited. Bob
  15. BobK

    Best Speaker To Use As Microphone

    A 6 inch speaker would make a terrible microphone. Why do you think you need down to 20Hz? If this is to pick up speech, which is implied by your post, 100Hz would be fine for a low end cutoff. And a good quality microphone would be far superior to any speaker at any frequency. Bob
  16. BobK

    popping actuator

    If it doesn't have to repeat more than once every several seconds, I think a good approach would be to use a gear motor to compress a spring, then a solenoid to release it for a nice pop. Bob
  17. BobK

    [woo] Does anyone know of this breakthrough technology ?

    Not very much, I would think. Bob
  18. BobK

    [woo] Does anyone know of this breakthrough technology ?

    Well, they have an out on the testing done by Intertek. They used a clean lab power supply for the test. If the device is supposed to clean up "dirty" power, then one could argue that it would have no affect on already clean power. I am not saying that the device works, only that the test was...
  19. BobK

    Blowing a 3A fuse with an AA battery?

    That is a dead battery. Bob
  20. BobK

    Bluetooth and Radio Frequency?

    I think you should look again at post #11 for the only solution you are likely to succeed with without months of effort. A pair of Bluetooth earphones has the Bluetooth transceiver and DAC already working. All you need to do is plug the audio out from it into an FM transmitter which you can...
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