Voltage signal boosting

[kevroy]

In my other thread, i asked how to trigger a circuit using a headphone jack. I am able to trigger using 3 NPN transistors in a darlington pair configuration (but using 3 transistors as oppposed to 2). I also have a 1 uf capacitor between the two touch points to isolate the DC coming from the headphone jack. I am able to get an LED to flash very dimly to the beat of the music, but i need to boost this somehow to trigger a 555 monostable (which i believe needs a trigger voltage to be at least 1/3 Vcc? which in my case is 5 volts).

Also, im using the audio coming out of my laptop, and i need to crank it all the way up just to get the LED to flash very dim. Is there anything i can do to fix that?

Thanks

 

[Prototyp_V1.0]

That coircuit isn't suitable for any audio input. If so you have to bias the input with a voltage divider and a cap.

Ant to make the circuit even more sensible, you can always put a third bjt onto it.

 

[kevroy]

thanks for your reply.

I just need this circuit to trigger a recording circuit when there is an output coming out of the headphone jack from the two way radio. There wont be any "audio" passing through this part of the circuit. Strictly just for triggering. I will try the voltage divider and capacitor to bias the input.

Thanks again