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  1. audioguru2

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

  2. audioguru2

    Keys finder circuit

    I know. It's asleep and is snoring. ;D
  3. audioguru2

    Keys finder circuit

    What kind of soft sound is it making, is it talking to you? ;D
  4. audioguru2

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

    Hi Pieter, It ain't complicated and it ain't a speed-limit alert. It's an RPM alert! ;D ;D If you want a speed sensor then drag a 5th wheel behind your vehicle. Or you could hookup something to your ABS sensors. You could slow the circuit's response time by increasing the value of the 1uF...
  5. audioguru2

    Keys finder circuit

    Hi Lapsap, D1 charges C3 very quickly when there is any sound, including common noise. Then the oscillator is started and the piezo transducer makes its sound. The only things in the circuit that I see to reduce sensitivity to low frequency noise is the high frequency resonance of the piezo...
  6. audioguru2

    DC offset for audio circuits

    Yes Alun. Good point! ;D ;D
  7. audioguru2

    Electronic Stethoscope

    Hi E, Welcome to our forum. ;D From the tests that I have made, body sounds are like this: 1) Heart. An extremely low frequency DC pulse, sometimes modulated at about 25Hz. 2) Lung. Normal breathing and athsma squeaking is from about 300Hz to about 10kHz. 3) Blood flow. Probably also from 300Hz...
  8. audioguru2

    DC offset for audio circuits

    Hi Walter, You are probably talking about the DC offset voltage at the output of an audio power amplifier that is direct-coupled to a speaker without a coupling capacitor. The offset voltage is the DC voltage measured at the amp's output that is applied to the speaker all the time. It is never...
  9. audioguru2

    Wireless Mic aeriel help

    If the receivers have a very good tuned circuit at their inputs, if you connect them together then the tuned circuit of one will be like a dead short to ground at the frequencies of the others. If they don't have an input tuned circuit then the single aerial will be loaded with an impedance only...
  10. audioguru2

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

    Each 100k pot should adjust from zero ohms to 100k ohms. Maybe your reduced range is because R12 is in series with it and R10 is in parallel with both in series.
  11. audioguru2

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

    Wire the pots with one side of them connected together like this:
  12. audioguru2

    Wireless Mic aeriel help

    You usually cannot put together the inputs to radio receivers without them loading the others down. The same happens if you put together the outputs of transmitters, and can damage them. Use 4 separate aerials. ;D
  13. audioguru2

    Electronic Eavesdropping Devices Detector

    You're welcome, Mareola. ;D Its great to hear that you got it to work.
  14. audioguru2

    Keys finder circuit

    A piezo buzzer usually has a transistor oscillator in it and therefore cannot be used as a microphone. Its oscillator will conflict with the oscillator in this project when it is supposed to be a speaker. Quote: Our project uses it as a microphone then drives it to make a sound.
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Costa, Horray and 3 cheers to you! Your power supply project worked fine all the time but you were fooled by a lousy current meter. You can make an accurate current meter by making a voltmeter and using it to measure the voltage across the project's R7. ;D
  16. audioguru2

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

    Hi Pieter, In the original project, didn't you remove R10? It scales-up the RPM range a little. I think R11 could be adjusted for higher RPM's if you reduce the value of R12 maybe to about 27k. Then the setting of R11 would be very sensitive near zero ohms so should also be reduced to about 20k...
  17. audioguru2

    Automotive 12V to +-20V converter

    Thanks, Alun. ;D Hi Jonathan, Thanks for your project but I don't think I need your voltage converter for my car. My factory-equipped 4-channel radio/CD player puts out about 14W per channel at low distortion into my high-quality 4 ohm speakers. Without modification, your voltage converter at...
  18. audioguru2

    Convert 12 VDC batteries to 8.4VDC

    Hi Ante, It is odd that Maxim don't give line, load and mains ripple rejection spec's for their switching regulators. Maybe they aren't very good and they don't want anyone to see them. A voltage regulator circuit would operate cooly and have excellent spec's if a switching regulator is used as...
  19. audioguru2

    Convert 12 VDC batteries to 8.4VDC

    Hi Even, The premium LM117 and LM150 cost much more than the LM317 and LM350. Their max operating current (5mA) is half the amount of the cheaper ones (10mA) so can use resistors that are twice the value, without the regulator's output voltage rising without an external load. I changed the 1uF...
  20. audioguru2

    Automotive 12V to +-20V converter

    I made a simple challenge because the project severely under-powers a pair of the excellent amplifier IC's that the author mentioned:
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