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

 

[jackorocko]

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.

 

[sgtpepperaut]

http://www.electro-tech-online.com/...h-relay-low-voltage-ac-source.html#post879237

getting somewhere on here..!

 

[jackorocko]

http://www.electro-tech-online.com/g...tml#post879237

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.

 

[sgtpepperaut]

i actually completed the testing and it worked without any problems!