Line out to mic line

hey i need some suggestions to solve a problem with my gsm-playground shield.
The shield has an onboard mic, but what i want is to play an audiofile from my computer.
So when you call the gsm-shield with your mobile phone you should hear music.

Can i get rid of the mic and connect an aux cable to the shield? Or use a digital to analog converter?

I also need a solution for the other way round. I want to record the shields audio output with an computer.

That is the shield that i'm talking about:

Thx in advance for any solutions.

A line-level signal is around 1V and a microphone signal is around 10-100mV (depending on the loudness and how close the line level is to the home audio or pro audio standards, etc.). Headphone-level is also close to line-level, so you can connect a headphone output to a line-input. (But, not the other way around... The voltage is OK, but the headphone impedance is too low for a line-output.)

So, you can use a [u]voltage divider[/u] (2 resistors) to knock-down the signal to somwhere between 1/10th and 1/100th of it's original voltage. You can experiment, or use a pot to make it adjustable.

But, that shield looks expensive! I'd be cautious about hacking it up! :astonished:

Also, since it looks like you'll be transmitting mono you'll need to mix the left & right channels together. Do NOT hard-wire the channels togther. You should NEVER connect two outpus together. (It's usually OK to connect two inputs together.) Put a resistor (1K - 10K) in series with each output. (Those resistors can be part of your voltage divider.)

And it's not a big deal in this case, but in-general, you'd like to avoid reducing line-level to mic-level whenever possible. All amplifiers add noise so there is added noise when you re-amplify the signal.

thanks for your help. it worked quite good, but as you said it's a bit noisy. is there any way to reduce the noise?