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  1. BobK

    Transistor amplifier

    I am surprised you get any output if the input is as described. It takes about 600mV on the base of the transistor to turn it on. In any case, even if it does amplify, it will do so with so much distortion as to be useless. A resistor from the battery + to the base, chosen to pull the...
  2. BobK

    Magnet coil help (turns, gauge, for coilgun)

    In order to get any efficiency at all, the current has to be limited by inductance and back EMF, not resistance. The capacitors can be charged over a time much longer than the firing time and can then supply much more current than the battery could supply. If I can charge the capacitors for...
  3. BobK

    analoge to PWM with a fixed 10 MHZ frequency

    You realize that the comparator must swtich in about 1 ns to make this work. I.e. 1% of the PWM frequency. And I repeat CDRIVE's question, whiy 10MHz? That is a bit high. Bob
  4. BobK

    Finding a good linear actuator

    Weight does seem like an approriate specification since he is talking about lifting. Bob
  5. BobK

    PIC10F200 and I2C communications?

    1. Why not choose a PIC with an I2C module? 2. You can do it with software, as long as speed is not a problem. Bob
  6. BobK

    Magnet coil help (turns, gauge, for coilgun)

    You shoudn't I was off by a factor of 10 in my first attempt. Edited. I can't even get that right. I was off by a factor of 100. Bob
  7. BobK

    Fixed voltage circuit

    Summary of this thread: "I really need some help, but I don't want to do any work, so give me the answers." "They are in the datasheet, and don't forget the capacitors". "I don't see them." <post of datasheet with answer circled> "Okay, after you circle the obvious answer in the...
  8. BobK

    Magnet coil help (turns, gauge, for coilgun)

    Let's do some calculations Some constants: length of barrel L = 1 m (I made this one up, but it seems reasonable) power from battery P = 5000 W mass of projectile m = 3.5g = 0.0035 kg Some variables: acceleration a time to accelerate t muzzle velocity v Some equations: v...
  9. BobK

    Voltage Drop

    Voltage drop is a somewhat unfortunate name for the phenomenon. If we say that a 10K resistor "drops" 10V at 1ma, what we are really saying is the the voltage across the resistor must be 10V in order for 1ma of current to flow though the resistor. The higher the resistace, the more voltage...
  10. BobK

    Fixed voltage circuit

    What is wrong with the one labelled "Typical Application" on the first page of the datasheet? Bob
  11. BobK

    Current Limiting and Heat

    Well, I was asking about the one that was producing excess heat, not the one that was not! So, if you are using 5 V and the forward voltage is 2.7 V then 2.3V/2.7 gives you .85A. To get 120ma, thre resistor should be 2.3/.120 = 19 Ohms. It will then dissapate 0.27W. Bob
  12. BobK

    Battery charging regime for low charge rate?

    Yep, they will not hold a charge for a year even. Bob
  13. BobK

    Current Limiting and Heat

    That is not a 1/2 Watt LED. That would be 55 mW. And dropping the voltage from 5V should have produced no noticeable heat. If you connected this to 5V with a 2.7 Ohm resistor, I would have expected smoke release. Bob
  14. BobK

    Charging 12v battery

    Or how long you have to charge it. Bob
  15. BobK

    Current Limiting and Heat

    What is the forward voltage and operating current of the LED? Bob
  16. BobK

    Battery charging regime for low charge rate?

    Charging at .1C for 18 hours would probably be okay, assuming they are nearly exhausted when you start. Bob
  17. BobK

    IC Help

    They were working normally before, as well :D Bob
  18. BobK

    SN74HC14N hex inverter.

    It is a logic gate that inverts the input and sends it to the output. (Actaully, 6 of them) Bob
  19. BobK

    Help! how to use BJT as voltage amplifier with Common-Emitter configuration

    You can get them on Ebay already built for less than you could make one yourself. Bob
  20. BobK

    Help with reading schematic

    Well, I will add this then: the compassator obeys alms law. Bob
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