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  1. audioguru2

    precision rectifier

    The LM324 is about the slowest opamp ever made a long time ago. The 1N4002 diodes are also very slow. The 330 ohm resistors have a very low value. The opamps are not biased. I have used a similar circuit with pretty fast opamps and diodes. Its resistors have a reasonable value. The opamps are...
  2. audioguru2

    AM reciever mixer

    Hi Walid, The mixer in an AM radio multiplies the input signal with the oscillator signal. I think the input signal amplitude-modulates the oscillator signal, producing multiplication that results in the sum and difference signal frequencies.
  3. audioguru2

    Energy saving device - can they work?

    Hi Stacy, Your "energy saver" wastes power when it is plugged in and a matched inductive appliance is not running. The wasted power is apparent power that is not measured by your billing electric meter. Since your "electrisave monitor" shows apparent power then it is a false indication of any...
  4. audioguru2

    Energy saving device - can they work?

    Hi Stacy, Welcome to our forum. ;D It is just a capacitor. If it is calculated to match the inductance of your running appliances then it reduces the power factor. Your electric meter does not measure power factor so you save nothing on your bill but your electrical utility company will use less...
  5. audioguru2

    Electronic Eavesdropping Devices Detector

    The other stations are all the FM stations, all the VHF and UHF TV stations and all the taxi cab radios. The Eavesdropping Devices Detector picks up a computer's interference so it might even pick up radiation from a radio and a TV.
  6. audioguru2

    Electronic Eavesdropping Devices Detector

    Yes, the Eavesdropping Devices Detector project has an untuned input so it picks up all high frequency signals. A computer makes high freqiency signals so it will detect them. A piece of metal doesn't make high frequency signals so the circuit should not detect anything from it. The supply...
  7. audioguru2

    Problem in an H-Bridge

    I don't know which Mosfet driver ICs you can buy, there are many of them. Get one that has a bootstrap diode for a boosted voltage to the gates of its high side Mosfets. Your Mosfets overheat because the 10k resistors charge and discharge their high input capacitance slowly and therefore they...
  8. audioguru2

    Electronic Stethoscope 2

    The Hemon project uses a PIC microcontroller that is programmed to be a counter.
  9. audioguru2

    Problem in an H-Bridge

    The Mosfets are old and therefore have a high on-resistance. They will get hot if the motor's current is high. Mosfets have a very high input capacitance that needs a fairly high drive current to charge and discharge quickly. The 10k resistor values are much too high for pulse-width-modulation...
  10. audioguru2

    Relay circuit with photocell

    Hi Pyro, Welcome to our forum. ;D The photocell has a resistance that is much too high to directly turn on your relay. Then the photocell should be used to turn on a transistor that can drive your relay.
  11. audioguru2

    using computer speaker amp for portable sound system

    The 12V transformer has a peak voltage of 17V which is reduced to 15.5V by the bridge rectifier. Then the power of a single-ended power amplifier is 2.4W at clipping into an 8 ohm speaker. When you fed 12VDC into the AC connections then it was reduced to 10.5VDC by the bridge rectifier and the...
  12. audioguru2

    Inverter

    The buzz comes from the transformer but I wonder if some sound is made by the backwards capacitors. The capacitors have a very high current pulse that causes them to heat (just before they explode) as a transistor conducts on one side and they quickly discharge into the "dead short" of the other...
  13. audioguru2

    Inverter

    Hi Freerider, Welcome to our forum. ;D The Inverter project does not work. It is too simple to be an inverter. Its capacitors are backwards and blow up. Its transistors have avalanche breakdown that wastes the small amount of power they produce. The transistors have a very low base current so...
  14. audioguru2

    Electronic Stethoscope 2

    The timer circuit is a counter. It counts seconds. It is easy to change it to count hearttbeats.
  15. audioguru2

    Two PCBs off of one power source

    The 68nF is a 0.068uF capacitor which is a standard value for a metalized plastic film type with a 5% and 10% tolerance. If you use 47nF instead then the boost peak will occur at about 62Hz where the input capacitor is cutting the very low frequencies and your tiny speaker can't produce 60Hz...
  16. audioguru2

    Timed Beeper...need help!

    R2, R3 and C1 are parts of a classic cmos oscillator. When the output of AND gate IC1D goes high then it stops the oscillator because D1 conducts. Yes, the beeps per second and the flashes per second will increase.
  17. audioguru2

    Two PCBs off of one power source

    Hi Bruce, It is easy to boost the bass frequencies foe an MC34119 amplifier simply like the LM386 amp does it. This modification has a voltage gain of 1 at high frequencire and a voltage gain of nearly 12k/3.3k= 3.6 at low frequencies. Bass boost works only if the sound source has bass...
  18. audioguru2

    Are datasheets important?

    Hi Herman, The CD4047 was used because it is an oscillator IC that has a digital divider so its outputs are a perfect square-wave, and it has two opposing outputs (one is inverted).
  19. audioguru2

    Are datasheets important?

    Hi Herman, Nobody was disrespecful to me: "Texas Instruments and Fairchild recommend a minimum of 10k ohms for the resistor in a CD4047 oscillator, then an inexpensive high accuracy capacitor can be used? Thank-you for pointing it out, Audioguru". I get thanks like this all the time.
  20. audioguru2

    Are there anywhere to request free photovoltaic cell????

    My electrical Utility gave away free solar garden lights. I got 10 of them. I can see them glow at night but they don't light up anything because they are dim. They have a single 1.2V AA Ni-Cad battery cell and a voltage stepup circuit. The dim LED is amber colour.
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