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  1. BobK

    USB + Switch + 5 LEDs

    That is better. What kind of lighted switch do you have? If it has only 2 leads and lights only when it is off, then that would be a problem. It is going to pass current through all the LEDs and they will all light dimly. If it has 3 leads and lights all the time, then it should work fine...
  2. BobK

    Has anyone ever built one of these?

    Even when the energy is coming from a known source (middle east) some pay with their lives. Bob
  3. BobK

    DC > DC converter problems please help!!

    There is not a current loss. The current used on input side times the input voltage must equal the current used on the output times the output voltage, except that is is not 100% efficient. So the equation is: Vin * In * efficiency = Vout * Iout Bob
  4. BobK

    USB + Switch + 5 LEDs

    First of all, the LEDs cannot be in series. The 5V that comes out of a USB port is only enough for 1 blue LED, which will need about 3.6V. So put the LEDs in parallel. Also you need a separate resistor for each LED when they are in parallel. Bob
  5. BobK

    DIY retracting License plate help.

    You do not need a servo that that. A motor that can push the plate in either direction, plus two limit swiches to turn it off when it gets to the final posisitions is all you need. The up / down switch would simply reverse the polarity on the motor and the limit swiches would be normally on...
  6. BobK

    Need help to build a flyback driver

    A 24V transformer is going to produce 33V DC which is way too much for either your filter capacitor or the NE555. You have probably blown these parts. Bob
  7. BobK

    AC Power Adapter Use

    No good. You need an adapator that puts out 18V and at least 0.5A. Bob
  8. BobK

    seemingly impossible class project

    Put a voltage across any device that is not a resistor and it does not obey Ohm's law, i.e. the current will not be constant and proportional to the applied votage. If it does obey Ohm's lay, it is, by definition, a resistor. Bob
  9. BobK

    capacitors for disengage a power source

    Using an opamp to run a motor seems like overkill to me. What you really need is a 3V supply and a transistor to switch the motor current on and off. They way you have it, the power opamp is going to dissapate as much power as the motor since it is reducing 6V to 3V. Bob
  10. BobK

    LDR Motor Circuit

    You need a resistor between the '741 output and the base of the transistor. Try a 1K. Bob
  11. BobK

    where should the ground be?!! x_x

    Connect it where you see gnd in the schematic. Bob
  12. BobK

    LED Circuit Design Help

    Okay, I get it now. Here is the improved circuit. No need for a divider on the output as the voltage on C2 quickly falls to zero when there is no AC input. Thanks Duke! Bob
  13. BobK

    LED Circuit Design Help

    It is not because of the divider driving the base of Q2. Can you explain where this extra diode goes exactly? I originally had a capacitor between the collector of Q1 and the D1 to block the DC, but that did not work, and I do not understand why. It initialilly charged C2 to the right...
  14. BobK

    Modelling Software Project

    Okay, if your goal is learning, have fun! But I would still study SPICE and make my software able to use models designed for it, since they are readily available. Bob
  15. BobK

    Modelling Software Project

    SPICE is open source and has solved all of these problems. You can get SPICE models for practically any analog device. It would literally take years of programming effort to match what SPICE does now. Why not start with that and add digital simulation for the devices you are interested in...
  16. BobK

    High output air ionizer

    Too bad the automakers are in a conspiracy with the oil companies to suppress all the simple modifications that double gas milage and halve emissions. Why not go for a hydrogen generator too while you are at it? Bob
  17. BobK

    LED Circuit Design Help

    Here is a cicuit I have simulated and it seems to work. The LED will start coming on at about 0.05V and be fully on at 0.1V and up. It consists of an AC amplifier, followed by a rectifier and integrator to get a voltage dependent on the input signal. It then uses a divider to feed the base of...
  18. BobK

    120Vac Night Light

    Or, you could go to the dollar store and get one for $1 that already has a photo sensitive switch. For a learning experience, buy two and take one apart! I suspect it uses an LDR + a triac. Bob
  19. BobK

    AC,DC absolute maximum parameter in datasheet of D flip flop

    I addition to what Steve said, they are NOT same as the reccommeded operating conditions, which is what you should design for. Bob
  20. BobK

    Choosing the appropriate ADC

    The voltage divider needs to have a low enough output impedance to meet the specs of the ADC. The impedance of your divider is roughly 3.3K. It this is not good enough, you can use a capacitor parallel to the 3.3K resistor, which lowers repsonse time, but is not a problem for this application...
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