Using a Trimpot with a Transistor?

[Aiden Attenborough]

Hi, I'm currently working on a very simple project for my pc, which is basically just a TiP31 Transistor connected to an audio jack and a strip of LED's which is powered by a molex connecter coming from my PC's power supply.

I currently have a cold cathode setup with a "sound module" that I bought separately at the time which doesn't work with an audio jack, but with a small microphone inside its case. It also has a variable resistor which is used to change the sensitivity of the microphone.

Is it possible to have a similar setup with the transistor? Is there any way at all to control the sensitivity? With a Trimpot possibly?

Thanks!

 

[kripacharya]

a few thoughts :

1) the audio output from PC jack is not sufficient to directly 'drive' a TIP31. So imo your basic setup should not work. You would need to pre-amplify the signal to do so.
2) if you already have a sound module, it would probably easier to modify this to work from the pc jack. You need to insert the jack's signal onto the output point of the active device (could be bjt or fet ?) which is connected to the mic. Connect a pot across the jacks 2 wires, and take the center pin along with the shield/ ground wire and use these into your sound module. I suggest you insert a cap in series here (say 1 - 10uF or so)

Start with the pot set real low, and boost it up till you get what you need.