Magic Transistor?

Discussion in 'General Electronics Chat' started by TehDawg, Feb 4, 2011.

  1. TehDawg

    Thread Starter New Member

    Feb 4, 2011
    Good day forum!

    This morning I had someone bring in a "water depth meter". I works by dropping a wire down the "bore-hole" and when the metal end touches water it makes a beep on the surface (The water closes the circuit).
    Now the device broke, and when we opened it, there was a 9V battery, a PNP transistor and a buzzer. One of the transistor legs were broken off. But strange enough we fixed it without the use of a transistor.
    My question now is, what was the transistor for?? We were stumped to figure out what it was for, and still don't have a answer. Any input is much appreciated!


    Teh Dawg
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    The transistor may have supplied gain, to ensure that the circuit would work even if the water was very pure (and thus of low conductivity) - perhaps you are testing it with less pure water?
  3. debjit625

    Well-Known Member

    Apr 17, 2010
    It was broken or it was never their,because many circuit use a transistors as a diode or in many case a kind of resistor also_Once I used the base emitter junction as a temperature sensor,that time I only needed the base and emitter pin and broke the collector pin and using that as a diode.

    Good luck
  4. SgtWookie


    Jul 17, 2007
    Well, you wrote "PNP transistor", but not the part number of it.
    It may have been a high-gain Darlington, like perhaps an MPSA14, that amplifies the current on the base by ~20,000. This is important if the water is very clean.