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  1. audioguru2

    electronic stesthoscope

    Our Electronic Stethoscope-2 project fixes errors in the original project. The errors are in the schematic and in the parts list.
  2. audioguru2

    Dark activated Lamp/LED not flashing 12volt

    There are many ways to make a dark-activated light that uses a very low current when there is light. A 741 is one of the oldest opamps and it uses a lot of current. Our project works well, what needs to be modified? http://www.electronics-lab.com/projects/motor_light/024/index.html
  3. audioguru2

    RC phase shift

    Kevin, Your article says and shows that the total harmonic distortion of the electrical voltage into homes is only 3.5%. The 3rd and 5th harmonics are only 1%. They have a graph on page 2 with the 3rd and 5th harmonics at more than 50%, but the voltage scale is in decibels (100dB full scale) so...
  4. audioguru2

    RC phase shift

    What are you talking about? The electrical waveform is a sine-wave. Its distortion is low so its 3rd harmonic is only about 1% of the amplitude of the fundamental. Its 5th harmonic is only about 0.75%. The most amount of harmonics are from a square-wave. Its harmonics have levels much lower...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Peter, Q1 and Q3 have 10k base resistors that supply a base current of 3.2ma. Their collector current is less than 32mA so they will work fine if ther beta is only 10 or more. The BC547 and BC557 have a minimum beta of 110 so any of them will work fine.
  6. audioguru2

    Please help on "Telephone voltage levels".

    In North America and in Europe we use DTMF touch-tones for dialing. Then a touch-tone decoder IC is used to give an output for each digit that is dialed. I have no idea if DTMF touch-tones are used for dialing in India. Ask people in India. You also need a circuit to detect that the phone line...
  7. audioguru2

    LG TV not powering on

    I got the service manual and many forums about the same problem with my Sony TV by simply entering its model number in Google.
  8. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    I think C2 is to prevent the DC at the output of IC1 from affecting the input DC voltage of IC2. C1 is just a filter for the DC reference voltage.
  9. audioguru2

    fm transmitter scematic required

    The circuit you want is illegal in most countries so people don't have it. It causes radio and TV interference. There are a few 1W FM transmitter kits available from Ramsey and Free Radio Berkley and are used by "radio pirates" who own ships at sea. A few of the newer kits are pretty good.
  10. audioguru2

    RC phase shift

    The electricity is a sine-wave and has very low harmonics. A square-wave has strong odd harmonics. The small amount of harmonics doesn't bother heaters, lights and motors so why worry about them?
  11. audioguru2

    IC 555 instead of IC 50240

    The microcontroller circuit is 9 years old and its IC might not be available anymore. It needs to be programmed. It doesn't have a pitch control and it has a buzzing square-wave output. A keyboard musical instrument can easily have a few keys "pressed" by an IC to make chords.
  12. audioguru2

    Transistor

  13. audioguru2

    IC 555 instead of IC 50240

    Years ago I bought an electronic piano for my kids. It is very high quality but was inexpensive and they are probably also available today. It has a pitch control so it can be adjusted to be in tune with other musical instruments. It has frequency dividers so its frequencies are always in tune...
  14. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    R4 and R5 have equal values and are in series across the supply. Their junction is a DC voltage that is half the supply voltage and is used as the DC reference voltage for opamp IC1 and for the opamp at pin 11 of the LM2917. The output of the parallel inverters is also about half the supply...
  15. audioguru2

    RC phase shift

    A 4kHz quartz crystal? It must be huge and cost a fortune. I wonder what uses it?
  16. audioguru2

    Temperature display with ICL7107CPL

    Hi Gayan, This is an LED meter with up to 19 LEDs draining the battery with 8mA each. Therefore the little 9V alkaline battery's life will be as short as 1 hour at which time the 7805 regulator won't regulate anymore because the battery's voltage will be less than the minimum of 7V that is...
  17. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    Oh yeah, 1000uF across the car battery and 470uF across the circuit will filter out alternator whine and things that turn on and off like turn signals very well. I have some 1000uF capacitors that are quite inexpensive and are small.
  18. audioguru2

    RC phase shift

    I have never seen a crystal produce a fundamental audio frequency. They are for high frequencies. Any waveform can be converted to a perfect sine-wave is you use a good lowpass filter to remove all the harmonics. My very low distortion sine-wave generator starts with a square-wave, then it is...
  19. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    The datasheet says the LM2917 can drive a load with up to 50mA.
  20. audioguru2

    5 volt to 3.3 volt

    5V isn't a high enough input voltage for an ordinary 3.3V regulator. There might be a low dropout 3.3V regulator available. Make a voltage divider with two resistors to get 4V. Then use an emitter-follower transistor to have an output of 3.3V at up to 200mA. The output voltage will change a...
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