Switching a Relay from a low voltage AC source

[sgtpepperaut]

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

[pyrohaz]

Hi, assuming that you won't need to switch at half the frequency of the sine wave, (12v automotive relays probably cannot do this) You should be able to go:

Half wave rectifier > Capacitor filter > Transistor switching Relay > Output!

The transistor amplifier section should be able to take the 1.8v peak from the capacitor and use it to switch the relay.