The card was designed as a two-layer PCB. Small size was a design constraint so we reduced space as much as we could.
The used sound chip was the Analog Devices AD1845 JP. We chose this chip because it offers parallel communication which simplified both software and hardware
for controlling the chip (We had little budget and time to have it running). We had to use the 68PLCC instead of the 100-TQFP package which is smaller,
because the casing was not available at the moment besides we had no equipment to do the soldering job.
We used Eagle for designing the PCB.
We used a PIC as the card controller which had basically two tasks:
1) Communicate with iDen phone through a Rs232 port that is part of the design, and
2) Acquire audio samples from the Audio codec.
We used analog input filters to eliminate noise in addition to a directional microphone.
Another design constraint was power. The sound card took power from the cell phone and we needed to keep power consumption as low as possible.
The iDen phone delivered a 3.2 V output so we used a DC-DC converter to reach the 5V input required by the Codec.
The Sound card was able to receive commands from the iDen phone, record real time audio and to play files stored in it 256 MB Scan Disk Flash Memory.