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  1. audioguru2

    Balanced Power Transformer

    Hi David, To avoid too much smoke if the primary winding is the wrong one, connect a 240V/40W incandescent lightbulb in series with one of the primary wires. If the connections are wrong then the light will be bright and limit the current. Connect the two black secondary wires together and...
  2. audioguru2

    Balanced Power Transformer

    Since you don't have loads, you are measuring some of the capacitive coupling of the wires inside the transformer. I guess that the secondaries are made the same, so if you connect the black wires together then the 120V windings are in parallel, not in series. Then the red wires would produce...
  3. audioguru2

    piezo buzzer using 555 ?

    The datasheet for a 555 or a Cmos %%% has the circuit for a monostable and a graph showing parts values vs time. How much current does your buzzer use? A 555 can supply up to 200mA and a Cmos 555 can supply up to 10mA. An NPN transistor has its emitter grounded and its collector connected to the...
  4. audioguru2

    piezo buzzer using 555 ?

    Instead of a flip-flop, you need to have a monostable timer circuit that is triggered by the voltage pulse to the locks then it times-out and turns off the buzzer. A 555 or a Cmos 555 could be used as a monostable timer but their trigger pulse is negative, a transistor inverter is needed.
  5. audioguru2

    Wireless (Radio) Headphones

    The internet has transmitter and receiver circuits that use only a few parts and can be made small. But most have very lousy performance.
  6. audioguru2

    Help On my mini dummy

    Why are you switching capacitors with such small values? Why is the exact value of each capacitor important? What is the input signal? What is the output signal?
  7. audioguru2

    Stepper Motor Driver

    The stepper motor driver has a minimum operating voltage of 10V. It probably has problems on lower voltages. People re-use the stepper motors from disc drives and CD players because they are very high quality. Most operate from 12V like this one:
  8. audioguru2

    Stepper Motor Driver

    A lot of guys have posted their own discrete H-bridge circuits that operate down to 5V. I have never seen a stepper motor that uses less than 12V.
  9. audioguru2

    Stepper Motor Driver

    Your motor need s voltage that is much lower than the 10V minimum of the IC's load supply. Get a stepper motor that operates on the higher voltage or get another IC.
  10. audioguru2

    Help On my mini dummy

    The shield of a shielded cable should be connected to the circuit's ground to work properly. Some circuits connect the shield to the output of a buffer amplifier that is carrying the signal so that the capacitance of the cable is cancelled. The stray capacitance changes when you change the...
  11. audioguru2

    Help On my mini dummy

    Two wires beside each other have capacitance between them. A shielded cable has a fairly high capacitance because the shield surrounds the center wire.
  12. audioguru2

    Q: how to build RGB led?

    The Mood Light project uses a new RGB LED that can handle a very high current of 350mA. You can build the project using ordinary little LEDs but they won't be very bright if you change the current-limiting resistors to supply no more than their 30mA max.
  13. audioguru2

    Help On my mini dummy

    Stray capacitance can be reduced by making wiring as short as possible.
  14. audioguru2

    Help On my mini dummy

    63pF is a very small capacitance. The wiring to it and terminals for it are a few pF and the shielded cable also adds capacitance. The switch has a few pf between its terminals. All the extra capacitance is called stray capacitance and must be compensated for in calculations for making an RF...
  15. audioguru2

    Stepper motor driver

    Most of the circuit's current is used by the motor so it is dissipating 12.25V x 225mA= nearly 2.7W. Maybe it gets hot because it is not designed to be driven with a voltage as high as 12V.
  16. audioguru2

    piezo buzzer using 555 ?

    The circuit needs to have a constant supply voltage. A piezo beeper has a tuned resonant housing and the piezo has an extra feedback terminal so its built-in oscillator oscillates at the tuned frequency for the loudest sound. If you make your own oscillator then it must be manually adjusted to...
  17. audioguru2

    piezo buzzer using 555 ?

    I was thinking of using a CD4017 counter. It needs to have an oscillator to drive it. The oscillator is triggered by the LED signal the the CD4017 would make the 3 beeps and its 4th output would turn off the oscillator for it to be ready to be triggered the next time. If the LED keeps flashing...
  18. audioguru2

    Class A amplifier Formulae help!!!

    It specifies "when operated with the maximum possible output signal". But then it has severe distortion, and the output power is difficult to measure because the waveform is not symmetrical.
  19. audioguru2

    piezo buzzer using 555 ?

    A piezo beeper might be loud enough when it is powered from only 12V. A 555 by itself will make a single long output (monostable) , or continuous outputs (astable)without stopping. A counter IC like a CD4017 and some diodes can make 3 pulsed outputs, then drive a transistor that drives the beeper.
  20. audioguru2

    Electronics kits...

    Don't make cheap kits. There are too many of them now. Most don't work or don't last long. Make kits that are designed properly and therefore they will be reliable.
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