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  1. audioguru2

    BJT biasing

    The signal at the collector of a transistor compresses half the signal because the collector resistor can't provide enough current. Therefore a constant current source provides a continuous current to stop the compression. The compression is distortion. The voltage gain of a common emitter...
  2. audioguru2

    Mains Remote-Alert

    Hi Cannibal, Welcome to our forum. ;D The project's text already explains how it works. Maybe first you must learn the basics of electronic circuits like darlington transistors, the Hartley oscillator type and tuned circuits. The transmitter sends a high frequency into the mains wiring and the...
  3. audioguru2

    BJT biasing

    If you use a constant current source circuit instead of a collector resistor, the gain of a transistor is very high and its distortion is low. The current source is a very high impedance so stray capacitance cuts high frequencies, and an emitter-follower is needed to drive any load. That is how...
  4. audioguru2

    transmission lines

    Because the source has a 75 ohm impedance and it matches the 75 ohm impedance of the transmission line and the 75 ohm impedance of the TV also matches the impedance of the transmission line, the response is pretty flat on a cable TV system from 50Mhz to 900MHz. The length of the line doesn't...
  5. audioguru2

    opamps

    An opamp has a non-inverting input (+) and an inverting input (-). A non-inverting circuit can have no gain (a gain of 1.0) by connecting its inverting input to its output. An inverting circuit can have no gain (a gain of 1.0) by using the same value for its input and feedback resistors.
  6. audioguru2

    BJT biasing

    The output impedance of a common-emitter transistor circuit without negative feedback is the collector resistor. Add a load and the signal across the load drops because of the current divider of the collector resistor and the load resistance. If there is negative feedback then when the output...
  7. audioguru2

    Question on the Plants Watering Watcher circuit

    OOps, thats right. When the soil is damp then the LED is off so the output of the gate is high. You can't increase the value of R8 from 47k or the output voltage folds and works like a mirror. The circuit will need an opamp to shift the output voltage from 0.0V to 5.0V.
  8. audioguru2

    Question on the Plants Watering Watcher circuit

    If you short the probes together the output voltage should be very low, close to 0.00V. My damp soil measures the same as a 47 ohm resistor and probably would make the voltage of your circuit very low. Try measuring the voltage with only a multimeter because maybe your microcontroller is pulling...
  9. audioguru2

    sony KP-E41Mh11

    Please don't post two posts the same. I answered you on your other post.
  10. audioguru2

    SONY Service Manual

    Google has a lot of information about Sony KP-E41MH11 but it is not in English. Maybe it is in your language. Google has a lot of information about the KV-25FXR1 in English, and had the service manual download for free for my Sony TV. Google has links to forums where guys discuss problems with...
  11. audioguru2

    Led Fade on Fade off

    Hi Steve, Welcome to our forum. ;D If a resistor feeds a capacitor then the voltage on the capacitor ramps slowly up as it charges then ramps slowly down as it discharges. An LED needs about 20mA so a ramping capacitor to power it must be huge. A transistor can drive the LED and the input...
  12. audioguru2

    transmission lines

    My cable TV company has many miles of 75 ohm coax around my city and has signals from 50MHz to 900MHz in it. It is 75 ohms everywhere and nothing resonates. In my home the 75 ohm coax cable from outside is connected to a 75 ohm splitter which feeds 75 ohm coax to my 75 ohm cable-modem and feeds...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Arman, An Amp-meter shows the current in the load. Here is the schematic modified with an amp-meter in series with the output transistors so its voltage drop is made-up bu the circuit. Or you can use Ohm's Law to calculate the voltage across R7. R7 is 0.47 ohms. 3A through 0.47 ohms...
  14. audioguru2

    Sound Level Indicator

    Hi Steev, Your TL082 dual opamps are completely different from the MC33172 dual opamps I used. You can use LM358 dual opamps but they have hiss and a poor high frequency response.
  15. audioguru2

    Blood pulse sensor

    Hi Yuri, Welcome to our forum. ;D I looked for Heart Rate Circuit in Google and saw many circuits. The most popular one is the HeMon: http://www.web-ee.com/Schematics/HeMon/HeMon.htm
  16. audioguru2

    a very simple FM Tx

    A few things affect  why his transmitters have poor range: 1) His battery is not new? 2) His radio has poor sensitivity? 3) His circuit layout is not compact? 4) His transistors are cheap Chinese copies? 5) His transmitting and receiving antennas are pointing in different directions?
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    An ammeter in series with the load causes a voltage drop that ruins the excellent voltage regulation of the project. Instead, connect the ammeter in series with the output transistors then its voltage drop is made-up by the circuit since it is inside the negative feedback loop. But maybe the...
  18. audioguru2

    class d amplifier

    Confusing, isn't it? Wouldn't it be nice if everybody drew the symbol for a Mosfet the same way?
  19. audioguru2

    class d amplifier

    Most semiconductor manufacturers have class-D audio amplifier ICs that are very complicated inside. A class-D amplifier uses switching transistors and Pulse-Width-Modulation. The duty-cycle of the high frequency pulses determines the average output voltage and the position of the cone of a...
  20. audioguru2

    Capacitor voltage

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