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  1. Hero999

    dual-output transformer

    The circuit will work without the 1N4001s which are only there to ensure the regulator doesn't get exposed to a negative voltage during short circuit conditions. The definition of GND is irrelevant as far as the operation of the circuit is concerned. GND or 0V is just the reference from where...
  2. Hero999

    PWM Without PWM IC

    It's a simple linear regulator not a PWM regulator. Why not build a circuit with the LM317 which is much simpler and will produce a much better regulator?
  3. Hero999

    Question about CMOS ICs, specifically 4516B - presettable up/down counter.

    Compare the package and the number of pins on the datascheet to the device, if they match, there's a good chance you have the correct datasheet. The correct full part number is CD4516.
  4. Hero999

    dual-output transformer

    That should be fine but you only need one bridge rectifier not two. Here's an example: http://www.electronics-lab.com/blog/?p=109
  5. Hero999

    PWM Without PWM IC

    It sounds like you're trying to build an inductorless switching regulator which is doomed to failure. Shorting the capacitor to 0V is just going to waste energy. Use a buck regulator which includes an inductor to limit the charging current and can be made with plenty of cheap controller ICs or...
  6. Hero999

    Re: Digital Stethoscope

    A microcontroller is the best way to do this but I'm aware that you don't want to use one as this is probably an educational project. I don't think you've given this enough thought. You can get CMOS 4000 series ICs which work directly from 9V, alternatively you could switch to four AA cells or...
  7. Hero999

    Looking for Capacitor

    Most component suppliers will stock a suitable replacement: RS Components, Farnell, Digikey etc.
  8. Hero999

    Making switching NPN with PNP

    Did you look at the link I provided? You only need two transistors.
  9. Hero999

    Looking for Capacitor

    It's a 18nF film capacitor rated to (I think) 1200V.
  10. Hero999

    [SOLVED] Is there a way to increase the breakdown voltage of a zener diode?

    There's nothing magical. It's a Vbe multiplier. The zener voltage adds to the transistor's Vbe. When the transistor's base voltage approaches 0.6V, it starts to turn on causing current to be diverted around it away from the Vbe junction. There's no way to mark a thread as solved. You've done...
  11. Hero999

    [SOLVED] Is there a way to increase the breakdown voltage of a zener diode?

    To answer the question exactly, here's how. The LM431 is a better option though.
  12. Hero999

    PSpice 9.1 Student version Download

    These sorts of problems are common with Vista. The solution is simple, download VirtualBox, install Windows XP as a virtual machine (you must have an old CD somewhere, if not pirate it) and install PSpice under XP.
  13. Hero999

    LDR offset + span adjustment

    I see so you want to scale from one range of voltages to another. That's possible but first, you need to know the range of input voltages as well as the output voltages. Here's an article: http://www.electrotap.com/blog/495
  14. Hero999

    LDR offset + span adjustment

    I'm not sure what you're trying to do. If all you want to do is make a voltage rise/fall depending on the light intensity all you need is an LDR and a resistor configured as a potential divider. I you need to reduce the output impedance then an op-amp or a transistor will work. The circuit...
  15. Hero999

    HELP! current booster.

    No, you can't get energy from nowhere, use more solar panels.
  16. Hero999

    How to distinguish between FM and AM transmitter circuits

    Reducing the values of R1 and R2 should increase the maximum frequency slightly, try changing them to 4k7 and 470R respectively.
  17. Hero999

    Please help me with High Low voltage cutoff with time delay

    You're on the right track. Look up diode AND/OR gates and give it some more thought.
  18. Hero999

    How to distinguish between FM and AM transmitter circuits

    That's not a Hartley oscillator, it's a Colpitts. I calculated the theoretical frequency to be 1.39MHz so it must be taking the transistor capacitance into account but whether it knows that the capacitance varies at different voltages is another matter. Yes, you need to increase the frequency...
  19. Hero999

    Please help me with High Low voltage cutoff with time delay

    Look at how the outputs of U2A and U2B in your circuit and compare the connections to my circuit.
  20. Hero999

    How to distinguish between FM and AM transmitter circuits

    There are three reasons I can think of: F= 1/(2π√(LC)) is only a an approximation. The resistance of the coil and load will also make a difference, a higher resistance or more loading will reduce the frequency. There will be some parasitic capacitance and inductance in the circuit so the...
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