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  1. BobK

    maximum power transfer

    Putting a resistor in series with a speaker will always reduce the power to the speaker. So what resistance will reduce it the least? Bob
  2. BobK

    Battery pack with indicator

    Stepping up from 7.4V to 12V will require 12/7.4 x the current from the batteries, plus the converter is only operating at 80 90% efficiency, so divide by 0.8 again to get the answer. It will require about twice the current from the batteries as you are going to use. Bob
  3. BobK

    0-10V DC Signal

    Two meters can read a voltage differently if they have a different input impedance, and it then depends on the output impedance of the voltage source. Try this, read the voltage out of your controller with your fluke meter with a 1K resistor across the output. See how that affects the voltage...
  4. BobK

    Crystal accuracy

    I am not sure what Harald is thinking, because his posts are usually quite accurate. But the way I read it, he is saying that dividing down a crystal will improve it's accuracy. This is not so. If the crystal is + or - 20 ppm (which is typical), the divided down frequency will also be + or -...
  5. BobK

    Command Script for Read/Write from USB Stick or SD Card

    To expound upon my previous answer: A USB stick FM transmitter reads MP3 files from a USB stick, processes them into audio, and transmits this audio on FM radio. This does not help with your problem of transmitting an image file. Bob
  6. BobK

    Command Script for Read/Write from USB Stick or SD Card

    Honestly, I think you haven't a clue. Bob
  7. BobK

    Digital Thermometer

    I would think these are avaiable for less money than you could make one. Is there something really special that it has to do, that you cannot get in a commercial unit? Bob
  8. BobK

    Command Script for Read/Write from USB Stick or SD Card

    ROFL Bob
  9. BobK

    Thermoeletric charging help?

    If you have a solar panel producing electricity, why would you create heat, then use that heat to create electricity at less than 100% efficiency? All you end up with is less power than you had coming out of the solar panel. You need to learn about thermodynamics before going for world...
  10. BobK

    Circuit board help

    Depends on what "this circuit board" is. You know, not all circuit board do the same thing. Bob
  11. BobK

    Thermoeletric charging help?

    You could boost it 1000V, but that would not give you any more energy. It is energy you need to charge a battery. As Steve already pointed out, your thermoelectric generator will produce an amount of energy that depends on the difference in temperature from the hot to the cold side. Body heat...
  12. BobK

    How to Connect to H Bridge?

    Exactly, which means you can use a single MOSFET to control each motor, no need for an H-bridge. Bob
  13. BobK

    How to Connect to H Bridge?

    Yep, you can use logic circuits. Oh, and why are you using an H-bridge? It should not be necessary if the robot only moves forward and it would complicate the logic to make it turn to stay on the track. Bob
  14. BobK

    Guns and Lasers

    First of all, photodiodes are probably a bad choice, there output is very small and will have to be amplified to read with an Arduino. You should use phototransistors, which can output a logic level signal. Then you could read then with the Arduino by multiplexing. 10 outputs and 10 inputs...
  15. BobK

    Thermoeletric charging help?

    Notice in link from the above post, that when heated by a candle, it does not produce enough power charge a cell phone. Heated by your hands, you will probably get a few milliwatts at best. Bob
  16. BobK

    How to Connect to H Bridge?

    It is a little more complicated than that. You want to change the direction by slowing one motor. And you need some logic. If both sensors are seeing white you want to slow one motor, and both are seeing black you want to slow the other. A microcontroller would be best. Bob
  17. BobK

    Thermoeletric charging help?

    Actually, thinking about it some more, you are not likely to get the current needed to make your phone charge directly. Phones need at least 500mA to charge. If you boosted from 1V that would be about 3A from the thermoelectric generatator. Your best bet would be to use a boost converter to...
  18. BobK

    Absolute beginner question about stereo jacks

    Paralleling them will not lose much volume as long as the amp can handle the combined impedance. If you have typical 32 Ohm headphones and an 8 Ohm speaker, the combined impedance is 6.4 Ohms, which is not that much different than 8 Ohms. I would expect a small drop in volume, not drastic. Bob
  19. BobK

    Command Script for Read/Write from USB Stick or SD Card

    You need a lot more and an "IC chip". To access a USB flash drive, you need a single board computer that can act as a USB host. As far as I know, an Arduino cannot do that, it only acts as a USB device, which is not the same as a host. A Raspberry PI would be more suitable. Bob
  20. BobK

    Searching...

    Have you ever noticed that subwoofers are BIG? There is a reason for that. It is very difficult to get sound at that frequency out of a driver the size of your pinky. Not sure at all what you mean by wireless here. Do you mean that you can control it via a wireless remote? Bob
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