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  1. audioguru2

    i need help extending the keys finder project. can someone help me out????

    I'm not finished with improving this project: 1) I tried driving my piezo speaker with two ordinary Cmos inverters paralleled, to get more drive current and it worked well but wasn't very loud with only 3V for a supply. 2) I tried two sets of paralleled inverters connected as a bridge to double...
  2. audioguru2

    need help on noise protection

    Hi Black Wing, I make many audio things and a few are RF. I keep the internal wiring compact by using Veroboard (never a breadboard) and use shielded audio cable on high impedance inputs. They don't pickup interference when mounted in plastic boxes. My latest Sound Level Indicator project has a...
  3. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Logan, I also had a difficult time trying to drive my piezo speaker with a low power Cmos IC and a low supply of only 3V to 5V. I looked for Piezo Beeper Circuit in Google and found this frequency response graph of one that shows how it has extreme resonance at only a couple of frequencies...
  4. audioguru2

    Low power switching

    Hi Tom, It sounds like you are making a dynamic microphone that is like a speaker with a moving coil in a magnetic field. Its power output is extremely low. Maybe you are making a "shaker" flashlight where you shake its magnet up and down inside a big coil and if you shake it long enough then...
  5. audioguru2

    Low power switching

    Hi Tom, Welcome to our forum. ;D Do you have a low voltage generator and want to rectify it into DC with low loss? Then step-up its voltage with a transformer like electrical utility companies do, then the 0.7V drop of each rectifier diode is negligible.
  6. audioguru2

    help with blue led

    Hi Got Lost, Welcome to our forum. ;D Your 555 LED flasher circuit doesn't have enough supply voltage for the voltage requirement of a blue LED plus the voltage loss at the high output of the 555. A blue LED's voltage requirement could be 3.6V. The voltage loss at the output high of a 555 could...
  7. audioguru2

    lm386

    Please don't post the same question in different forums. I answered in your other post.
  8. audioguru2

    sensitive parabolic michrophone

    You don't need an amplifier when you connect a microphone to the mic-input on a computer. If you want to record the faint sound of bubbles popping and the computer's gain isn't high enough, then you need a microphone preamp circuit. An LM386 can be used as a mic preamp if a low-value coupling...
  9. audioguru2

    Newb question: identifying leads on unmarked MOSFETS?

    Digikey sells brand new Mosfets with spec's and a guarantee. An IRF540 is only $.63US today in small quantities and costs less if you buy 25 or more.
  10. audioguru2

    sensitive parabolic michrophone

    1st of all, it's an LM386. 2nd of all, you don't say if you want it to amplify the computer's output so you can hear a speaker play what's stored on the computer, or if you want to amplify something then connect the output of the LM386 to a line input on the computer so it can be recorded.
  11. audioguru2

    Newb question: identifying leads on unmarked MOSFETS?

    Hi Shelby, Since the gate of a Mosfet doesn't draw DC current, you could connect a 9V battery in series with a 100k resistor and apply it to two pins to try to turn it on. Then since you don't know if it is N-channel or P-channel you could try another 9V battery in series with a LED and a...
  12. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Logan, I tried the oscillator section driving my piezo speaker. My opamp is a CD4069 ordinary one, not a high power CD4049 so it didn't have enough power to drive the piezo speaker unless the supply voltage was at least 4V. It wasn't very loud so I connected the piezo from pin 15 (your IC's...
  13. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Logan, When pin 5 of the IC is grounded, its pin 4 should go to 3V, its pin 2 should go to ground and its pin 10 should go to 3V. Then D2 becomes reverse-biased which allows the oscillator to drive the piezo speaker. I copied the values of the oscillator's R10 and C5 from the Keys Finder...
  14. audioguru2

    Transformer Power Rating

    Your resistor doesn't look like it is the same as a modern one. Use a modern one.
  15. audioguru2

    i need help extending the keys finder project. can someone help me out????

    1) To test the beep oscillator and the piezo speaker, temporarily connect the IC's pin 5 to ground (the negative wire of the supply). 2) Measure R1's 4.7k resistance with one end disconnected from the circuit, maybe it is bad. 3) Replace the electret microphone. Before (with 22k) its voltage was...
  16. audioguru2

    NiMH Charging

    It is very dangerous to connect anything to a charged Ni-Cad or Ni-MH cell without current-limiting. They are capable of supplying many amps and a discharged cell will attempt to charge with many amps. They might explode! For many years, two series strings of 6 AA Ni-Cad cells were in parallel...
  17. audioguru2

    i need help extending the keys finder project. can someone help me out????

    A piezo speaker doesn't have a polarity. If more than one is used then they all should be wired the same. Only a piezo beeper with a built-in transistor oscillator has a polarity.
  18. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Logan, The project's value of 22k for R1 with a 3V supply is incorrect! I just tried it with my electret mic and got only 0.3V across the mic and it barely worked. When I replaced it with 4.7K then it had 1.9V and worked fine. Replace your circuit's R1 with 4.7K and try it. ;D
  19. audioguru2

    Horn Sound when The mic is close to LoudSpeaker!

    DSP can reduce feedback by analysing the sound then adding a frequency notch filter at a frequency that is oscillating. Your pc would need a program that can do that. An omnidirectional mic picks-up sound from all directions so would probably make feedback worse. A unidirectional ot cardioid mic...
  20. audioguru2

    Led display Digital Voltmeter question

    Of course it needs a rectifier to read AC. If you want accuracy with low levels then the rectifier should be an active one that uses an opamp.
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