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  1. BobK

    Extend Dell LCD Screen?

    Let me google that for you: http://www.lmgtfy.com/?q=monitor+cable+extension Bob
  2. BobK

    What are the cuttoff frequencies ?

    I am sure somebody can, I am not sure somebody will. Bob
  3. BobK

    where would I buy a 300 amp 1.5 volt transformer

    He want to make a shower of sparks out of molten metal. In his backyard. Glad it is not my backyard. Bob
  4. BobK

    amplify ultrasound signal

    The intensity is going to fall off as the square of the distance, so the intensity at 20feet on axis will be about 1/50th of that at 1m, i.e. -34db So I think you are going to have a lot of trouble getting 105db at that distance, and 180 degrees is also very difficult. You need to know the...
  5. BobK

    Basic transistor Guitar Amp

    Except that 9V is the wrong voltage to use. The junction of the two emitters in my circuit sits at 4.5V and swings up and down from there, so the Vce is never as high as the calucution you are using. And on top of that, each transsitor is hard off for half the cycle and it is the average power...
  6. BobK

    measuring AC ripple on 5 volt PS

    How much did that famous O-ring cost? Bob
  7. BobK

    RAIL GUN capacitor size/power questions???

    A capacitor charged to 5V could only kill you if you try to swallow and choke to death. A large enough capacitor charged to 100V could give you a fatal shock. One charged to 5000V (you won't find any at a reasonable price) will likely kill you unless you are very cautious. Bob
  8. BobK

    Basic transistor Guitar Amp

    Why don't you show me where I am wrong? Bob
  9. BobK

    Is this mosfet good for my project?

    If you are only switching something once, the frequency is 0. In that case, what you have to worry about is only the delay in switching it. If 10uSec is fast enough, then you are fine. Bob
  10. BobK

    hih4030 voltage drop

    And with an 80K divider you are likely to run into problems with the input requirements of the ADC. I think you will need an op amp in between. Bob
  11. BobK

    Transistor drive question

    Also, depending on what you are doing, there might be better devices, a MOSFET for example. Bob
  12. BobK

    amplify ultrasound signal

    I re-read your OP and I think you do not need the kind of power you were talking about. The sensitivity rating of a speaker gives the output in Db at 1 meter with 1 Watt input. Each 6Db after that will need double the power. So if you find a tweeter rrated at 90Db at 1W it will put out 96Db at...
  13. BobK

    Electromagnets?

    1. Wind the coil on a 1 inch core instead of a 3 inch core. (BTW increasing the number of windings also increases the field) 2. Only if the applied power is AC. On DC the poles remain contant. Bob
  14. BobK

    Is this mosfet good for my project?

    The RC time constant between the 900pF gate capacitance and the 10K resistor is 10uSec, which is fine when you are operating at less than about 10KHz, which you are by a factor of 10000, so I think you are ok.:) If you ware trying to switch at 100KHz you would be in trouble. Bob
  15. BobK

    Basic transistor Guitar Amp

    Here is a circuit I found for a 1 Watt discrete amplifier. http://darrenyates.com.au/electronics/archives/25 The BC337 is similar to a 2N2222. Bob
  16. BobK

    help me make led lamp like this

    I said that in the last post, I estimarte 105ma. However, you should not make it that way, you should use a separate resistor for each string of LEDs. The resistor would then be calculated to drop the difference between 12V and the forward votage of the LEDs in the string at the desired...
  17. BobK

    help me make led lamp like this

    That is a 20 Ohm resistor. Assuming it is operating at 12V and each LED is dropping about 3.3V, the resistor is dropping 2.1V, so there is 105 ma total current. So it in the right range at least. The problem with this arrangement is that the current will not be equally balanced between the 8...
  18. BobK

    Basic transistor Guitar Amp

    CDrive, Okay, I will do the calculation. For 1 Watt output into an 8 Ohm speaker the RMS voltage has to be 2.8V. The push-pull stage will have one side of the speaker at half the 9V so the transistor has to drop, on average, (4.5-2.8)V or 1.7V. The current for 1W output into 8Ohms is 2.8/8...
  19. BobK

    James Bond CIA Gadget Challenge

    If you can get the victim to pierce the skin on both hands with needles on opposite ends of the pen, it becomes quite easy. Bob
  20. BobK

    Is this mosfet good for my project?

    The 10K resistor in the level shifter will cause the MOSFET to switch off very slowly. This may or may not be a problem, depending on how fast you need to switch. At what frequency is this going to be switching? Bob
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