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  1. audioguru2

    Two PCBs off of one power source

    Hi Bruce, You showed the parts layout of the sound effects unit. Its speaker can be replaced by a resistor with the same resistance and it will work. But I have no idea what is the output circuit of your FRS radio. It is easy to make the input of an MC34119 power amplifier into a mixer by...
  2. audioguru2

    Help!! My Door Alarm is not work?

  3. audioguru2

    Two PCBs off of one power source

    Hi Bruce, The speaker connects directly to the S8050 which is a PNP transistor and to the positive supply voltage. So the speaker is the DC load for the transistor. The speaker must be replaced by a resistor with the same resistance then the output can be capacitor coupled into a resistor that...
  4. audioguru2

    Cut Phone Line Detector

    Wall jack? Aren't you connecting this circuit to a telephone jack? A positive voltage at the base of the 2N3904 NPN transistor turns it on. The turned on 2N3904 transistor turns on the 2N3906 PNP transistor that turns off the IRF510 N-channel Mosfet. When the Mosfet is turned off then the buzzer...
  5. audioguru2

    Lowpass filter for subwoofer

    Why doesn't somebody fix this confusing project so that the schematic, the pcb layout and the parts list agree???????????????????????????????????????????????????????????????????? Or else just dump this project.
  6. audioguru2

    Two PCBs off of one power source

    We are just guessing at the circuits. Maybe the speaker is a transistor'e AC and DC load. Then the transistor won't work properly with a 10k mixing resistor, it needs 8 ohms then a mixing resistor. If the outputs have DC on them then they need coupling capacitors to block their DC from messing...
  7. audioguru2

    Help!! My Door Alarm is not work?

    "Most radio frequency circuits like this one do not work on a breadboard" Make a pcb or use stripboard with very short wiring.
  8. audioguru2

    Electronic Stethoscope

    Hi Cs, Welcome to our forum. ;D The output of the Electronic Stethoscope 2 project feeds an AC without any DC bias voltage to headphones. The output pin 5 of the LM386 power amplifier IC is also AC but it has a DC bias voltage of half the positive battery voltage. It swings from about +1.2V to...
  9. audioguru2

    Cut Phone Line Detector

    The phone line has polarity like a battery has. Maybe your phone line is connected with backwards polarity. Reverse the green and red phone line wires to the circuit's input. Try connecting a 9V battery to the inputs to see if the buzzer stops when the circuit detects the battery voltage.
  10. audioguru2

    "Power?" Inverter

    The max input to your RadioShack transformer is 2A. It is overloaded if the output power is more than only 19.2W.
  11. audioguru2

    white led

    Hi Pier, I don't know which LEDs you have. If they are the Lumileds Luxeon I then the max continuous current is 350mA if they have a good heatsink and their forward voltage is from 2.31V to 3.99V. Use a 12 ohms resistor to limit the current while you measure their actual forward voltage...
  12. audioguru2

    Electronic Stethoscope 2

    Hi Soly, Is your negative battery getting hot because something is shorting it? Your voltage readings are all too high and are positive which looks like the negative 9V supply voltage is missing.
  13. audioguru2

    Why is so hard to mimic the Knight Rider scanner Effect?

    Thanks AN920, It is much clearer and is 1/5th the number of bytes.
  14. audioguru2

    "Power?" Inverter

    Hi Cvscam, If your voltmeter is not "true RMS" then it reads the output voltage of the square-waves with an error of about 1.414 times high. Therefore its 105V is really only 74V and the 60W bulb draws only 25W. Did you connect the capacitors backwards like in the schematic? Did they get hot?
  15. audioguru2

    Why is so hard to mimic the Knight Rider scanner Effect?

    Hi AN920, You made a nice circuit. ;D Smearing effect? Because it is a fuzzy JPG file type instead of a very clear GIF or PNG file type? I "enhanced" the JPG smear. A GIF or PNG file type has no smearing.
  16. audioguru2

    white led

    Then the LM317 gets warmer. The current is regulated so it remains the same. We don't know what is the actual voltage of the LEDs because the voltage is a range of voltages and each LED is different. The LM317 needs about 2.5V to operate plus the current setting resistor needs 1.25V, plus the...
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Rufinus, Good, you fixed it. ;D Now you can measure its performance. The voltage regulation is much better if you do not connect a current meter to its output. Measuring the voltage across R7 is a very good way to measure the current used by a load. All my test equipment are not grounded...
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    82 ohms, 2W should not get hot. It will be very warm which is fine. A 1W resistor will be hot.
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Rufinus, Your Q2 and Q4 transistors are not working. Maybe D10 is shorted or it is connected backwards.
  20. audioguru2

    white led

    If you use 1.2 ohms then the current will be about 1A and your expensive LEDs will blow up! Check the max current for your LEDs (350mA?) then calculate a suitable current-setting resistor. 3.9 ohms will give about 320mA.
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