how to ADC for analog phone?

[tuanvoi]

Hi all,
Could you please give me some hints about how do do A/D conversion of an analog signal coming from an analog phone to digital signal. I will be using PIC18F4550, 40 pins. Could you please show me how to do this conversion in C programming for my PIC18F4550. Thank you so much.

 

[duffy]

Set the A/D converter up to run at it's fastest rate for your pic clock (but not too fast or you will loose bits, check the table) and use Vcc as a reference. Run the phone speaker through an audio isolation transformer. Amplify that signal with an opamp, bias the opamp to 1/2 Vcc, set the gain so the peak is under Vcc. Use the A/D interrupt to read it as fast as you can. Process or transmit or save or whatever during the conversions.