Sound chip for the Personal IRIS

[Sanjay Iyer]

In article <8908311403.AA05313 at zorac.DCIEM.DND.CA>, tim at zorac.dciem.dnd.ca (Tim Pointing) writes:
> > The sound chip exists on all Personal Irises.  The only documentation is
> > the man page for the driver /dev/audio.  You will need to get a speaker
> > and microphone.  The PI has miniature audio jacks in the back.
> 
> Does anybody have any info on things like leves and impedences for these
> jacks or are they some "standard"?


This ought to help:

            PERSONAL IRIS AUDIO I/O INFORMATION

Line input:

       +/- 2.5 v (input is AC coupled) is full scale to ADC
       ADC is 8-bit, 2's complement
       Input impedance is 22K ohms.
       Input gains not adjustable.

       Frequency response:
           20 Hz -  13 KHz @ 32K/sec sampling rate
           20 Hz - 6.6 KHz @ 16K/sec sampling rate
           20 Hz - 3.3 KHz @  8K/sec sampling rate

Microphone input:

       +/- 3.8 mv (input is AC coupled) is full scale to ADC
       ADC is 8-bit, 2's complement
       Input impedance 330 ohms.
       Designed for use with 300 ohm microphone.
       Input is summed (analog) with line input.

Output:

       With full output gain (0xff) and no load, output swings +/- 4.9 v.
       Reduced output gain linearly reduces swing.
       Output is AC coupled (~4 ohms in series with 220 uf).
       Can directly drive 8 ohm speaker.

(By the way there is no single sound chip; the audio circuit is composed of
 a combined ADC-DAC, another DAC for output gain control, a switched-capacitor
 filter, and misc amps).