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Transistor replacement and some other questions.

Discussion in 'Electronic Basics' started by John Jardine, Jul 16, 2004.

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  1. John Jardine

    John Jardine Guest

    I'd be very inclined just to use more of the BC548/BC558's. They're easily
    good for the 20ma's or so needed for the tweeter and relay.

    What should have been shown on the diagram for both ac adapter use and/or
    batteries is something in the area of a 220uF 16V capacitor across each of
    the DC rails. In fact, in the case of the sender, I'd say without one you're
    nearly guaranteed spurious oscillation.

    Wouldn't have thought it matters which way round the transmitter transducer
    is connected. With a combined TX RX the best way to go is just to try it.
    The main problem would be sound cross coupling but that would have been for
    the manufacturers to sort out in the first place. (that is assuming the
    module is designed to send -and- receive at the same time)
  2. Rubicon

    Rubicon Guest


    The ultrasonic circuit link below has two transistors that I can't
    locate - SL100 and the SK100. I'm thinking of replacing them with
    BD139 and BD140. Can anyone suggest better replacements than these?

    In addition:
    What kind of supply filtering is needed when using batteries instead
    of an adapter "wall wart"?

    Which is the common trace on the transmitters tranducer and as the
    transducers I have are the combined transmitter/receiver type will
    this cause a problem with these circuits?


  3. Rob Paisley

    Rob Paisley Guest


    The positions of the PNP and NPN transistors should be reversed.

    But: -

    The 555 has a bipolar output , therefore, the transistors and diodes
    can be eliminated and the transmitter connected directly to pin 3 of
    the timer.

  4. Rubicon

    Rubicon Guest

    Thankyou for your replies.

    I have been trying to get this it working without success but now
    hopefully I'm sorted.

    One last question though. If a transducer was placed at the end of
    long shielded wires are there any extra components required for
    correct operation?


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