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  1. audioguru2

    differentiator

    You can pass an AC current through a capacitor just like it is a piece of wire.  ;D
  2. audioguru2

    TDA1554 22W Amp

    I think the LM386 is too small for this application. Our Mini-box 2W project is fine.
  3. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Olihou, I don't think the kits have errors, only the schematic and/or the pcb pattern so that circuits and pcb's copied from them don't work, but the kits work fine.  ;D
  4. audioguru2

    Increasing the range of Transmitter

    Hi Alun, The impedance ratio of a transformer is the square of its turns ratio. So if half the winding is 75 ohms for the antenna, the full winding has twice as many turns therefore is 300 ohms. ;D I see what you mean that the transistor without bias will conduct for a very short period and...
  5. audioguru2

    TDA1554 22W Amp

    You are going to add a stereo mixer and a stereo amplifier only for a telephone? All you need is a little 1W mono amp and a little speaker. Keep the radio separate. You won't get 22W per channel with our project anyway. It is rated with a very high supply voltage of 14.4V. In your car the...
  6. audioguru2

    Increasing the range of Transmitter

    Hi Alun, If the antenna impedance is 75 ohms, the total impedance of the center-tapped coil will be 300 ohms. When saturated, the transistor will have a collector current of about 30mA into the 300 ohms load. If the base bias resistor is 47k, the beta will need to be 170, about right. I see...
  7. audioguru2

    Increasing the range of Transmitter

    Hi Alun, I'm afraid that you designed a nice little heater. I figured a typical beta of 200, but its max is 300 and will be more when heated. I don't know how many volts of output the transmitter will have. It must have a peak of about 0.8V (I don't know where you got 2.1V from) or our output...
  8. audioguru2

    TDA1554 22W Amp

    Hi Sherbo, If you connect amplifier outputs together, severe damage might occur to both of them: 1) If both amplifiers are turned on, they will fight each other and produce unlimited current. One will go one way and the other will go the other way or try to hold the output at zero if it doesn't...
  9. audioguru2

    differentiator

    Kevin, An opamp integrator doesn't have an RC time constant. It has the constant current times the reciprocal of the capacitance. An opamp integrator also doesn't have dvdt. The rate doesn't change because the charging current is constant.
  10. audioguru2

    Data sheet for UA759U1C

    Yeah, HotWaterWizard is our datasheet champion!  ;D Even Fairchild's website never heard of it and they invented it.
  11. audioguru2

    Increasing the range of Transmitter

    Hi Alun, The Belkin transmitter automatically turns off when the input music ends. Then your transmitter amplifier will probably release its majic smoke!  ;D It would be wise to bias it off, and let the RF from the transmitter turn it on and let it amplify as class-C:
  12. audioguru2

    RJ45 network card to IR

    Hi Ali, The highest frequency crystal listed in my Farnell/Newark catalog is only 25MHz and they are all surface-mount. Digikey have many crystals but the highest frequency is only 50MHz, some are for through-hole mounting.
  13. audioguru2

    PWM

    Hi Kiwi, Here is a link to the technical description of motor speed controls for wheel chairs and golf carts, many running on 24V. The 555 PWM speed control and its limitations are discussed and better circuits. Nearly everything is covered including coasting down a steep hill which generates a...
  14. audioguru2

    Increasing the range of Transmitter

    Hi Alun, I think that it is worth trying a TV cable amp/splitter at the transmitter, some even have a gain control. The Belkin FM transmitter has a range of a whopping 3m for a good signal! It runs on only 3V so I don't think it has much output to overloading anything.  ;D
  15. audioguru2

    differentiator

    Kevin, You can have a simple integrator where a capacitor is charged and discharged by only a resistor. The slope of the capacitor's voltage is curved as it charges or discharges because as it charges, the voltage across the resistor becomes less, resulting in less charging current so the...
  16. audioguru2

    RJ45 network card to IR

    Hi Ali, The circuit has changed a lot since last year. It had a 9V battery. 1) The author says it won't work with 74HC series because they are too slow. Other people say 74HC is fine. 2) I don't think it will work. Its photodetector diode is backwards. 3) I have never heard of crystals that...
  17. audioguru2

    Increasing the range of Transmitter

    A cheap cable TV amplifier/splitter might work.
  18. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Duke, Sometimes kit-makers put errors on purpose on their schematics and pcb patterns to stop people from simply copying them. It is fun for me to try to re-engineer what is correct. Besides the opamp wiring and parts differences, all around the diode looks odd. The RF section of this...
  19. audioguru2

    Electronic Stethoscope

    Hi Dazza, You're right, its best to keep any kind of radiation away from your unborn child. I learned about Dick Smith Electronics, the surplus parts place, on another website. They sell used cars too, don't they?  ;D On the other site are guys making circuits for their guitars. They break all...
  20. audioguru2

    Increasing the range of Transmitter

    Hi Monkeyman, Welcome to our forum. It is nice to chat to you here instead of over there. ;D A guitar amplifier goes up to about 20kHz. FM is at 100MHz, 5000 times higher!  ::)
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