How to use an audio codec as an ADC?

Question

I would like to add ADC functionality to a TI C6748 dev board. I need 16bit precision, but relatively low sample rate(~5K).

Not finding any suitable daughter ADC card, I am considering the possibility of making use of the on board stereo codec TLV320AIC3106. I notice its analog input voltage range is quite limited (-0.3V ~ 0.3V). But my input voltage range is 0~5V.

Do I just need to scale the signal amplitude such that it falls into [~0.3V ~ 0.3V] range? Any other implications that using an audio codec as a general purpose ADC?

Answer 1

You just need to scale the voltage and adjust the DC offset (if needed). There is an important thing to know when doing this, however.

Audio ADC's often have high pass filters, two of them actually. The first is a cap in series with the signal path. The second is a digital filter that is inside the ADC. These filters usually remove anything from 0 to 10 Hz, but sometimes it could be as much as 0 to 200 Hz. Sometimes you can disable these, but usually not. If you are using the ADC for non-audio this might be a problem for you.

• Rocketmagnet: I think that's a very important point to stress. If you just connect, say, 0.3v to the input, you won't read out a value of 0x7FFF, you'll probably get something like 0x0000.