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  1. audioguru2

    noob question.

    The output is supposed to be an AC signal with an average DC voltage of 0V. The article says, "C1 is a coupling capacitor to remove DC from the output." So if your circuit has DC on the output then C1 is shorted or connected backwards, or the load has DC on it.
  2. audioguru2

    switching 12Vdc with 3Vdc

    A relay has a coil with a low resistance that needs a fairly high current at a certain voltage. Your AVR can't drive a relay coil directly, but the AVR can drive a transistor that can drive the relay's coil. The relay's coil is an inductor that makes a high voltage spike when its current is...
  3. audioguru2

    12v power supply?

    It is perfect for holding 8 AA battery cells to make 12V. But a charged and charging car battery is 13.8V. Yes.
  4. audioguru2

    white led

    Heatsink compound (the white paste) should always be used between a semiconductor's metal surface and the heatsink. It fills microscopic valleys and scratches with the compound that conducts heat very well. The film of paste must be very thin and the items should be tightly bolted together. The...
  5. audioguru2

    Electronic Stethoscope

    Hi Greg, I just finished replying to your duplicated post. Please do not make duplicates of your posts.
  6. audioguru2

    Electronic Stethoscope 2

    Hi Greg, I am glad that your project works well. ;D It uses unregulated 9V supplies which will be fine for a Cmos counter circuit. A TTL counter circuit would need a 5V low dropout regulator and a few other parts. The AC signal from the output of U4 could feed through a 10k resistor into 1/6th...
  7. audioguru2

    Simple dB meter driver circuit.

    The meter circuit posted by MP is a frequency meter, not a VU dB meter. A VU meter shows audio levels, not the frequency of a tone.
  8. audioguru2

    Problem With Ultrasonic Motion Detector

    The output must be low for the LED to light. Your output is not low, it is high so something is wired wrong. The collector of the transistor must go down to 1.8V less than the 9V supply for the LED to be very dim. The collector must go down to 0.2V for the LED to be bright and for the relay to...
  9. audioguru2

    Problem With Ultrasonic Motion Detector

    I don't know if the pins on the BD639 transistor are connected backwards. I don't know if your old 7490 counters have a supply bypass capacitor and a regulated 5V supply. The circuit doesn't have enough power to drive a relay unless the transistor has very high gain, but most don't. Change the...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    There are more than 29,000 members here and I am the only one who fixes these lousy projects that don't work properly.
  11. audioguru2

    Help the Newbie

    The nichrome wire might have destroyed the 555 IC. The max allowed output current from a 555 is 200ma. Your nichrome might use 5 times that or more. Also, a little 9V battery doesn't have enough power to heat nichrome wire for long. Maybe only a few seconds. You need a power transistor at the...
  12. audioguru2

    Simple dB meter driver circuit.

    I haven't seen a tape deck for about 15 years. My cassette deck had LED VU meters.
  13. audioguru2

    Driving an LCD backlight with FETs or transistors?

    Hi Blueroom, A PIC has a max output current of 25mA so a base resistor value of (5V - 0.9V)/25mA= 164 ohms will allow the transistor to saturate the best. Use 180 ohms. I used 680 ohms for the Mood Light because its current per LED never gets anywhere near 350mA. 
  14. audioguru2

    Driving an LCD backlight with FETs or transistors?

    Hi Blueroom, I made some LED "flashlights" (they flash 5 times in half a second then pause to cool for half a second. The LED is blasted with 90mA for 30ms so it is very bright and its 9V battery lasts a long time). I tried 2N7000 Mosfets and 2N4401 transistors and they both performed the same...
  15. audioguru2

    Constructing a RadioController Car - Help!

    We can't see your pictures because that website is "forbidden". Why don't you attach the pictures to your reply here?
  16. audioguru2

    High Power LED Mood Lamp

    A 2N3904 is NPN like the BC548 and a 2N3906 is PNP like a BC558. They have their pins opposite to the European ones.
  17. audioguru2

    Need sugestions about virtual ground or symetric supply for OPAMP

    The ambience circuits produce the difference between channels. Mono is cancelled because it is the same in both channels, no difference. Bass is usually in mono. So the bass is cancelled which leaves nothing but its harmonics which is distortion. A Butterworth 2nd-order filter is 12dB/octave, a...
  18. audioguru2

    Need sugestions about virtual ground or symetric supply for OPAMP

    Hi Wellington, Vinyl records and tapes had terrible high frequency phase balance between channels. It causes distortion when you use a circuit like you have that extracts the difference (ambience) between channels. Reducing the value of the input capacitors killed the deep bass. Each 10k...
  19. audioguru2

    High Power LED Mood Lamp

    The 2N4401 has identical spec's to a BC337, a max saturation voltage of 0.7V with a collector current of 500mA and a base current of 50mA. Their pins are reversed. The 2N2222A has a max saturation voltage of 1.0V at the same currents.
  20. audioguru2

    High Power LED Mood Lamp

    That is the highest voltage that can be used without breaking it. That is the max threshold voltage for some of them to barely turn on when they conduct only 250uA. The curves show that a typical one conducts 350mA when its Vgs is 4.5V. You cannot buy a sensitive one. They are random.
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