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Switching a relay from a low voltage ac source

Discussion in 'General Electronics Discussion' started by sgtpepperaut, May 18, 2010.

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  1. sgtpepperaut

    sgtpepperaut

    3
    0
    May 18, 2010
    hi there,

    i am currently working on a project that involves a cellphone that puts out ~1.3 volts AC signal to the speaker/vibrator. I am trying to switch a 12 Volt standard automotive relay with whenever that vibrator/speaker goes off (ie when the phone gets called)

    wondering if anyone has any info on what hardware to use to make this possible.

    I was reading about transistors and MOSFET amplifiers but i am not quite sure that i can simply hook the ac source up to the base and have 12 volts at the collector putting out 12 volts at the emitter.

    Any info is appreciated! thx
     
  2. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    I had plans to do the same thing. I figured a couple diodes would rectify the ac to dc then have that turn on a transistor to switch the relay. But 1.3 volts is really low voltage for a pair of diodes. You'd be losing half of that across the diode. Maybe a transformer is needed to boost the ac signal. my knowledge is lacking in that category still.
     
  3. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    pretty much what I just said, but I am still concerned over the low voltage. diode will drop ~.7 volts. that leaves you with .7V Add in a resistor to control current and you on the lower limit of what a transistor will need for it to saturate fully.
     
  4. sgtpepperaut

    sgtpepperaut

    3
    0
    May 18, 2010
    i actually completed the testing and it worked without any problems!
     
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