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  1. BobK

    USB Power

    You would use a DC-DC converter. But as I already explained, you cannot draw enough power from a USB port to power the devices you want. Bob
  2. BobK

    Bike trainer concept I've been messing with in my head

    Funny that you didn't mention that you intended the alternator to provide mechanical resistance. Now it makes more sense. It still does not seem like a good way to measure distance. The output will vary with speed. You would have to calibrate it and integrate the output power over time. Bob
  3. BobK

    stereo amplifier

    I misspoke when I said to get a subwoofer amp. This one, at least, filters out everything above 200Hz, so that is not good. You just want a full-range amp. Try to get one that does not have that much power since the suggested amp only has 45W. Any audio amp that can drive a 2 Ohm load...
  4. BobK

    stereo amplifier

    The impedance of the device is shown as 3 Ohms. The kind of amps people us in car stereos for the subwoofers can typcially drive down to a 2 Ohm load, so I think you should look at these as a cheap solution. You would need to provide 12V power which you can also get fairly cheaply. Bob
  5. BobK

    Beginner getting into electonics - help please

    Coca Cola an John Monks, I think one of you is analyzing a circuit with 1 LED and the other one with 40 LEDs in parallel. Bob
  6. BobK

    Easter engine problem

    But still a very long way to go! Bob
  7. BobK

    USB Power

    That is a total power of 4.7W. A USB 2.0 port can supply only 2.5W and a USB 3.0 port can supply only 4.5W. So you are out of luck even at 100% efficiency for converting the 5V power to 12V. Bob
  8. BobK

    Bike trainer concept I've been messing with in my head

    If all you are trying to do is measure the distance, counting wheel rotations is much easier and more accurate. Bob
  9. BobK

    Isolation b/w DAC & Power amplifier

    I just gotta ask: what does a smoothed sine wave look like? edited: never mind, I see that it is a DAC output, so smoothing (usually know as filtering) does make sense. Bob
  10. BobK

    Measuring distance moved using an Accelerometer

    The integration is not difficult ... if the device stays in the same orientation at all times. If it is rotated, I think it becomes quite a difficult problem. edited: perhaps even impossible without using a gyro. Bob
  11. BobK

    Hallowen project (LED)

    You cannot do that with a single 555 timer. You would need several and some other logic. You would be much better off with a microcontroller. Also, where did 35Hz come from? At that frequency, it would get at most a shimmering effect, not flashing like lightning. Bob
  12. BobK

    Infrared and gps and connectivity

    This has to be the most ill-conceived project I have seen yet. Bob
  13. BobK

    I (a newb) would like to design a small & simple GPS tracking system for my 2 cats

    You are not likely to be able to build one for less than this. $79. http://www.ebay.com/itm/GPS-GSM-Personal-Spot-Tracker-Tracking-Location-Device-Real-Time-Tracer-Pet-GPRS-/140813151538?pt=US_Tracking_Devices&hash=item20c91e2d32 Of course the initial cost is only part of it, you will...
  14. BobK

    About LED Sign Board

    That will get you enough for 5 alphanumeric characters, not much of a signboard. Bob
  15. BobK

    Power Generation, Voltage fluxuation and regulation.

    Yoiu can think of the smoothing capacitor as follows. If you simply rectify AC with a bridge, the voltage will go to zero twice in each cycle. To get DC you have to be able to provide power all the time. The capacitor charges when the AC waveform is above the design voltage, and it discharges...
  16. BobK

    About LED Sign Board

    The forward voltage of LEDS is mostly determined by their color. Red are typically around 2V and blue, green and white typically around 3.6V. Bob
  17. BobK

    Beginner getting into electonics - help please

    If you got a reading of 13.6V on the DC Voltage setting of the multimeter it is a DC supply. When unloaded, an unregulated supply will typically read higher than the rated voltage just like yours did. When drawing the rated current it will read closer to 12V. The fact that you read 3.2V when...
  18. BobK

    Building a CPU That Works

    If the idea is just to design a cpu at the gate level and then realize it in hardware, I would suggest that an easier approach would be to use an FPGA development board. No soldering required, and the result would be something that would perform, well, like a modern cpu. bob
  19. BobK

    lap timing circuit

    Yes, and you could also use a person with a stopwatch. Bob
  20. BobK

    Beginner getting into electonics - help please

    5W at 12V = 400ma. Assuming something like 3.6V for the LEDs, you get 20 strands of 3 LEDs, more that the OP is getting by doing it wrong. Bob
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