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  1. audioguru2

    Electronic Eavesdropping Devices Detector

    It looks like the same circuit as in our Projects section but its C8 is backwards and it doesn't have a sensitivity control. It has a few parts missing around the detector diode and the speaker doesn't have a current-limiting resistor in series. I didn't check the values of all its parts. S1...
  2. audioguru2

    Oxygen Sensor Tester (Design Idea)

    My old car passed the emissions test. But when I drove away I floored it which left the testing place filled with too rich black smoke!
  3. audioguru2

    LED pulser help

    My geek-talk said that the TLC272 opamp is too wimpy to supply enough current to the transistor. Use the original LM358 opamp which has about 16 times more output current. It should work fine.
  4. audioguru2

    LED pulser help

    The overloaded transistor needs to have a high base current to turn on. The TLC272 is a Cmos opamp that has a low amount of output high current. The opamp's output is trying to go high enough to switch the comparator (first opamp) but the high base current holds down its voltage so that it...
  5. audioguru2

    LED pulser help

    I and most datasheet sites don't know what is an LM272. They have an L272 which is very different from an LM358 dual opamp ued in the project and won't work in this circuit. Maybe the very heavy load on the transistor melted it so that now it is shorted?
  6. audioguru2

    PH meter

    Design a circuit or steal it from another site or from a datasheet. Make a clear schematic, parts list and description about its parts and how the circuits works. Then see "Publish Your Circuit" instructions on the Home page.
  7. audioguru2

    very loud alarm help please

    An LM386 amplifier IC has an output power of only 0.5W into an 8 ohm speaker with the square-wave signal from a 555 oscillator. Exactly the same power as from the 555 directly into the speaker. A piezo beeper like in smoke alarms has a built-in oscillator/driver that automatically tunes itself...
  8. audioguru2

    PH meter

    Hi Steve, Anybody can post a project. Why don't you?
  9. audioguru2

    very loud alarm help please

    If the supply voltage is more than 6V then you are straining the poor little 555. It is not designed to drive an 8 ohm speaker. A power amplifier with a fairly high supply voltage will drive an 8 ohm speaker loudly. With a 6V supply, the output power of the 555 into an 8 ohm speaker is only...
  10. audioguru2

    white led

    My bright red wide-angle LEDs are these ones: MV8191.pdf
  11. audioguru2

    Sound Level Indicator

    Shielded audio cable is used to join a microphone to a preamp and to join any audio source to an amplifier. It has a center signal conductor that is surrounded by the grounded shield. It stops mains hum and other electrical interference that would be picked up by ordinary wires. I can buy a...
  12. audioguru2

    white led

    Hi Pier, Aren't your LEDs connected in series? Then the current through each one is exactly the same and the LEDs don't need to be the same. They just need to live up to their current rating. I bought my factory-sealed bag of 100 Fairchild LEDs online from Digikey. They were probably from the...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Chapz, An N-channel power Mosfet needs to have its gate at a much higher voltage than its source to turn on. Then this modified project would have a max voltage output of only about 26V instead of 30V.
  14. audioguru2

    Sound Level Indicator

    Since R15 connects to +5V then it makes a voltage divider with the resistors in the IC which makes pin 6 about +0.5V. Without a signal, pin 5 of the LM3915 is supposed to be 0V. Then none of the LEDs will be on. When a signal causes +16mVDC at pin 5 then the first LED will turn on. 22.6mVDC...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Chapz, Welcome to our forum. ;D The 0.33 ohm emitter resistors are used to equalize the gains of the output transistors because the 2N3055 transistor has a wide range of current gain. Members who tried 0.22 ohm emitter resistors reported that one transistor became much hotter than the other...
  16. audioguru2

    white led

    Fairchild and all the other major semiconductor manufacturers make hundreds of excellent LEDs at a good price. I recently got an e-mail from the distributor where I bought mine that mine are now discontinued and I could have bought the last ones they had. I didn't buy any more because better...
  17. audioguru2

    Silly transistor question, Voltage to the base

    The base-emitter junction of a transistor is a diode. It limits the voltage to about 0.7V when it is forward-biased and conducts  like a zener diode when its reverse voltage exceeds about 6V. You do not apply a voltage to the base of a transistor. You apply a forward current. An...
  18. audioguru2

    white led

    Hee, hee, hee. ;D ;D ;D I bought a bag of 100 LEDs made by Fairchild. Every one is absolutely perfect and they were a pretty good price.
  19. audioguru2

    Sound Level Indicator

    If the battery gets hot then something is is drawing too much current. Did you use an MC33172 dual opamp? Did you use an LM2931Z-5.0 low-dropout voltage regulator?
  20. audioguru2

    white led

    Are your LEDs manufactured by a major semiconductor manufacturer?
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