Search results

  1. audioguru2

    High Power LED Mood Lamp

    The PIC has a max allowed output current of 25mA. When it is driving the nearly dead short of a base-emitter diode then the current is as high as 60mA, because it is HC Cmos. Of course series base resistors are needed to limit the current and limit the power dissipation in the PIC. A few people...
  2. audioguru2

    Resonator datasheet needed

    His is 10.7MHz which is a wideband ceramic filter for the IF of an FM radio. Microcontrollers also use a 3-pin ceramic resonator but they are narrow-band and are 0.5% accurate. Digikey has a 4.000MHz 3-pin ceramic resonator with the capacitors built in for only $.34US each. Ceramic filters for...
  3. audioguru2

    High Power LED Mood Lamp

    The expensive high power LED is rated for a very bright 350mA per LED. With a base current of only 430uA then the transistors supply typically only 86mA of LED current. What a waste! The cost of using base resistors with the correct values: NOTHING! Why not? I wonder what value of base...
  4. audioguru2

    Cutoff frequency and 3dB points

    There are lots of definitions for the cutoff frequency.
  5. audioguru2

    Cutoff frequency and 3dB points

    Wikipedia agrees with the output at -3.01dB down (half-power) for a cutoff frequency. It doesn't matter what type is the filter, Butterworth, Bessel or Chebyxxxx.
  6. audioguru2

    Cutoff frequency and 3dB points

    3dB is chosen as the cutoff frequency amplitude because it is half-power and is noticeable by most people as a small reduction in the level of sound or light. 6dB is half or double the amplitude.
  7. audioguru2

    High Power LED Mood Lamp

    Are the resistor values correct in this nice new project? http://www.electronics-lab.com/projects/games/005/index.html The red LED has a forward voltage much less than the green or blue but it has the lowest current-limiting resistor value. Therefore if the transistor saturates then its current...
  8. audioguru2

    Choosing PA for my 3-way active Cross over circuit

    Hi Shahriar, Look at the sensitivity spec's and power ratings for the speakers. A sub-woofer has very low sensistivity so needs a very high power, a woofer has low sensistivity and needs high power, a mid-range has medium sensitivity and needs medium power and a tweeter also needs a medium power...
  9. audioguru2

    Electronic Stethoscope

    Pin 4 (and pin 2) of the LM386 should be connected to ground (0V). Because the original project has an error in its parts list and says to use a 741 opamp for U5. A 741 won't work with its pin 2 connected to its pin 4 but works a little with -9V on its pin 4. Pin 5 of the LM386 has a DC voltage...
  10. audioguru2

    Motorola's circuit doesn't work.

    Processor? Didn't you connect the Motorola transistor circuit to an RS-232 signal?? The RS-232 signal doesn't come from the processor. It comes from the pc or from a modem at a dual-polarity fairly high voltage and fairly high current signal. The microprocessor circuit you showed in your other...
  11. audioguru2

    how to use a microphone as switch

    Hi Hussain, Welcome to our forum. ;D 1) If the microphone is an electret type, then power it through a resistor from a filtered positive voltage. 2) Amplify the microphone signal with a simple opamp amplifier circuit. 3) Rectify and filter the opamp's output then you will have a "1" when there...
  12. audioguru2

    Need to design a filter to allow only voice frequencies

    The article posted by Yoyok shows how much better a 4th order filter attenuates outside the bandpass than a 2nd order filter. The circuit posted by me is a 2nd order filter but is inverting.
  13. audioguru2

    Motorola's circuit doesn't work.

    Hi Mik3ca, The circuit should work fine with +12V, -12V RS-232 signals if they aren't too fast. With the input at +12V then 11.3V will be across the 100k resistor resulting in a base current of 113uA. The datasheet of the 2N3904 shows that it saturates very well with its collector current 10...
  14. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi TooExpensive, Welcome to our forum. ;D The threads are long because they should be divided: Theory about why the original circuit doesn't work, Max ratings of parts, Substitute parts, Heatsinks, Adding meters, Troubleshooting etc. Somebody should post a new project about what they have done...
  15. audioguru2

    High Voltage Stun Gun !

    Hi N4, Welcomr to our forum. ;D You can make a well-insulated voltage divider for your meter, or buy a high voltage probe for it like this one:
  16. audioguru2

    Audio amp quiscent current

    Marantz was an extremely high quality American hi-fi equipment manufacturer, probably the very best. Now they are Japanese-owned and use cheap Sanyo and Toshiba parts. Their owners also bought McIntosh and Boston Acoustics. Amazing.
  17. audioguru2

    Audio amp quiscent current

    Maybe Marantz copied Sanyo's circuit. Increasing the value of the pot turns on the transistor, then the idle current is reduced. A resistor is on the other side of the transistor to turn it on, reduce its value to reduce the idle current. It would be difficult to find a trimpot the same...
  18. audioguru2

    Audio amp quiscent current

    If your amplifier circuit has a trimpot to adjust the amount of idle current then it will connect to a transistor or couple of series diodes connected to the outer of the 3 pins of your new module. Probably the new module passes a different amount of current through the adjustment part so it...
  19. audioguru2

    Digitally controller PSU

    To have a 35VDC regulated output, the circuit needs a 30VAC transformer. 30 x 1.414= 42.4V peak, minus 2V for the rectifier bridge and minus 1V of ripple in the filter capacitor = 39.4V unregulated. If you power a 5VDC/4A regulator from unregulated 39.4V then the heat in the series pass...
  20. audioguru2

    Help with circuit troubleshooting

    You forgot to attach your schematic showing its part numbers and its supply voltage.
Top