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  1. BobK

    Coil winding resistance.

    You still are not getting it. If you draw energy out of the system you have to put more energy in. If you are spinning the magnets without the coils connected, it will take a certain amount of energy to spin it agains the mechanical friction. If you then start drawing out electrical...
  2. BobK

    Problem with test wiring for DIY ipad dock

    I hope you noticed this line: For use,you need to add matching heatsink to this power amplifier while working. If you run this without a heat sink it is not going to last long. Bob
  3. BobK

    Coil winding resistance.

    Only if the coil windings are connected to something so that current is flowing in them. The reason it happens is becuase when current is flowing in the coils they make a magnetic field that opposes the magnets, so they push against the magnets and resist the rotation. Lef's suppose it did...
  4. BobK

    Transistor how much current is needed to activate them?

    The 5'th is the center tap on the primary (which will be the secondary for you). You want to connect the side with 2 wires to the audio and use the other side as the output. The 3 wires gives you two choices for the output. Choose the one that gives you enough output from Harald's circuit but...
  5. BobK

    Transistor how much current is needed to activate them?

    The one I linked to is smaller and cheaper than a power transformer would be. It is the type of transformer used in old transistor radios whcih duke suggested. Are you in the U.S.? If so, there must be a radio shack nearby. Bob
  6. BobK

    Transistor how much current is needed to activate them?

    http://www.radioshack.com/product/index.jsp?productId=2103254 An amplifier is much more complex. Bob
  7. BobK

    Transistor how much current is needed to activate them?

    Why are you ignoring Harald's solution that does not need power when that is what you originally wanted? Bob
  8. BobK

    LM7805

    Trust but verify! Bob
  9. BobK

    Super Powered Battery?

    If you are indeed talking about something to heat a tent, there is already a very cheap and efficient solution. http://www.amazon.com/Coleman-SportCat-PerfecTemp-Catalytic-Heater/dp/B0009PUPSI/ref=sr_1_2?ie=UTF8&qid=1336138348&sr=8-2 Look at these specs: Product Features 1,500 BTU...
  10. BobK

    High speed Mosfet

    A simple pull down or pullup resistor on the MOSFET gate (depending on which would turn it off) might do the trick if the problem is that the gate floats when the 5V2 turns off. Bob
  11. BobK

    Intermediate digital project

    A digital dice game could be fun. It would involve a clock (oscillator) counters, and decoding logic. 1. The easy way: Use a 7-segment digit to output 1-6. 2. The more challenging way: have spots arranged like this: 0 0 0 0 0 0 0 0 0 And do the...
  12. BobK

    led systematic to layout

    Wabajig, You misunderstand the use of the resistor in driving LEDs. It is to provide a negative feedback to any increase in current in the LED, which can happen, for instance, as they heat up. Essentially, it is an el-cheapo current regulator. And LEDs (even the the same part number)...
  13. BobK

    High speed Mosfet

    Before looking to kludge to correct the problem caused by a drop in the 5V2 supply, shouldn't you try to find out why it is dropping out? Bob
  14. BobK

    battery discharging circuit/ battery full charge detection

    Plus the internal resistance times the charging current. Bob
  15. BobK

    LM7805

    The 7805 has a dropout voltage of 2V, which means to get 5V out you need 7V in. Your 6.3V 1/2 A transformer + rectifier + capacitor will not provide 7V at any signifcant current. Think about switching to a low-dropout regulator like the LM2940, which has a .5V dropout. Edited: Simulation...
  16. BobK

    Conversion from [-10,10]V to [0,5]V range

    Except that it is deriving it's reference from the same 5V supply and is therefore subject to exacly the same variation my method would be. Edit: Actaully, if you put a capacitor across the lower resistor in your divider, you would get increased stability of the 2.5V reference, so that might...
  17. BobK

    Conversion from [-10,10]V to [0,5]V range

    You could eliminate the op amp making the 2.5V reference and instead use a 5K to 0V and a 5K to 5V on the + input. Thevenin's equivalent theorem says this is equivalant to 2.5K to 2.5V. Bob
  18. BobK

    Determining which pin on a component corresponds to the pins on the data sheet?

    There is a dot marking pin 1 and the pins are then numbered counter-clockwise from there. The block diagram is not any indication of where the pins are on the package. Bob
  19. BobK

    Sun light sensitive switch

    A solar panel would be overkill. A light dependent resistor would be smaller and cheaper. Edit: Here is an exmple of a simple circuit: http://pcbheaven.com/circuitpages/Light_Dark_Activated_Relay/ Bob
  20. BobK

    electromagnet help

    A coil wrapped around the outside of a non-mangnetic tube would do that. There are plenty of coil gun sites on the web. Bob
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