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  1. BobK

    Boost converter

    That is why Oliver said you need an external (MOS)FET. Bob
  2. BobK

    PCB & Pricing

    ExpressPCB will give you 3 copies of a single board 2.5 x 3.8 in only for $51. They are very high quality. And they supply a very easy to use schematic capture and PCB layout program (which locks you into them for manufacturing). I have used them and was very happy with the result. Please...
  3. BobK

    capacitors as batteries

    The one advantage of capacitors over batteries is that the charge / discharge rate can be many times higher. If you could build an electric vehicle that runs on capacitors you could charge it in minutes as opposed to hours (with the right power equipment.) bob
  4. BobK

    IC 555

    That is what "active low" means. The trigger input is activated when the signal is low. Bob
  5. BobK

    Need help understanding importance of Inductance

    The voltage across an inductor is proportional to the rate of change in current in the inductor. Think about what that means when an inductor has some current flowing in it and you suddenly break the circuit. In an ideal world the current has to go instantly to zero and thus the voltage...
  6. BobK

    Reversing switches

    No, no ideas. That is why I wasted my time telling you how to wire it and what kind of switch you could use. Bob
  7. BobK

    Sound in Electronics

    A square wave has strong harmonics at 3, 5, 7 and all odd multiple of the fundamental frequency. This causes it to sound harsh because there is too much high frequency content. A sine wave, on the other hand, has no harmnoics and sounds not very interesting. A low pass filter will give you...
  8. BobK

    Calculate PWM power

    Gee, that never happens to me :D. Bob
  9. BobK

    Homemade Battery Recharger w/ Regulator -- HELP!

    But 3 x NIMH batteries is 3.6 V! There are battery management ICs that do what you want and actually use the correct algorithm for charging the batteries. A "simple" charger will reduce the life of NI-MH batteries significantly. Try Linear Technologies, for example...
  10. BobK

    Calculate PWM power

    Resqueline, Steve, I thought I said that :) Bob
  11. BobK

    Sound in Electronics

    What Steve said. Thanks for clarifying my post. Bob
  12. BobK

    Transistor/ current question

    You also need a resistor from the micontroller to the base of the transistor. BE is a diode, so this also looks like a short when the output is high. This is likely pulling more current than the miccontroller can safely ouptut. Bob
  13. BobK

    Sound in Electronics

    Simply take the output of each and run it through a resistor to the speaker or the amp input. If it is going directlly to a speaker, use 33R resistors. If is is an amp input use something like 1K. Bob
  14. BobK

    Calculate PWM power

    Method 1 is incorrect. When the LED is on, both the current and voltage are at peak values. So if you get the average of each, you have multiplied by the duty cycle twice instead of once. That said, you results are even more perplexing, becuse method 1 should have produced 66% of method 2...
  15. BobK

    I need a tutorial on MOSFET gate resistor selection

    In a DC to DC converter no diode is needed (except the ones in the circuit itself). The circuit is already designed to direct the current to the load when it is switched off. In the case of a motor, you want a diode (not zener) directly across the motor inputs, placed in the reverse polarity...
  16. BobK

    I need a tutorial on MOSFET gate resistor selection

    Case 1: The gate threshold of a MOSFET is NOT the voltage you need to apply in order to saturate it. If you look at the datasheet, the threshold of 2-4V that you quote is the voltage at which the MOSFET will pass just 250uA, not much help when you want it to carry 5A. If you look at the...
  17. BobK

    Need HELP, simple timer project

    Since no one else is answering, I will give you the bad news. I don't think you are going to find any way to do this without some serious electronics experience. If you have a couple of months, and want to learn a lot, go for it. Else find a friend who has this knowledge or hire someone...
  18. BobK

    555 Outputs Conflicting (I think) - hellllp

    Because it feels so good when you stop (i.e. solve the problem?) Bob
  19. BobK

    Reversing switches

    Here is a latching pushbutton switch that might work for you. http://www.mouser.com/ProductDetail/E-Switch/P227EE2B18A/?qs=sGAEpiMZZMvxtGF7dlGNppIc3%2fi6SWt4e1pBNs8YrNQ%3d If you need only 100 or 200 ma, there are smaller and cheaper options, but I doubt that that is the case. Bob
  20. BobK

    Reversing switches

    If you want a single pushbutton (momentary contact) switch to reverse the motor you will need some logic and power transistors or relays. If you used a toggle switch (dpdt) you can do it all with switches. If you can find a latching pushbutton dpdt switch, this could also work with no...
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