Can I create extra auxiliary ADC by using a external analog mux to a ADAU1701?

Hello,

The SigmaStudio software that generates code to run in the SigmaDSP core will only allow you to poll the auxiliary ADCs once per audio frame, and it will only allow you to add 4 instances of the auxiliary ADC input cell, so you'll need an external microcontroller to do a bit of work in order to make this possible.

My suggestion would be to do something like this:

The microcontroller would have to follow these steps:

Read ReadBack1

Write that value to DC1

Read ReadBack2

Write that value to DC2

Read ReadBack3

Write that value to DC3

Read ReadBack4

Write that value to DC4

Toggle the signal that controls the multiplexer for the ADC signals

Read ReadBack1

Write that value to DC5

Read ReadBack2

Write that value to DC6

Read ReadBack3

Write that value to DC7

Read ReadBack4

Write that value to DC8

Toggle the signal that controls the multiplexer for the ADC signals

Repeat

By repeating this process over and over in the microcontroller, you will have 8 cells in the project (DC1 through DC8) that will contain the values of the 8 analog signals external to the SigmaDSP.

Hi Brett,

That's a neat idea to vart "DC" sources via serial control from a uC. Can one take it a step further and use the microcontroller's own ADCs for the analog inputs?

Hi Bob,

Yes, you could certainly do that. A "DC" source in SigmaStudio just acts like a variable that gets an address in parameter memory assigned to it. You can have the microcontroller update that memory location with whatever it's reading in on its own ADCs.

Brett.

Thanks for your help! This means we can pass quite a large set of numbers from a uC into a SigmaDSP and use them just about anywhere in the schematic! I did not even suspect such a possibility till now.

Bob

Yes, the DC Source cells simply act as (input) memory placeholders that you can write from an external uC as needed.

Similarly, the DSP Readback cells act as (output) memory placeholders that can be read by an external uC and used for anything imaginable.

I would like to read from e.g. eight potentiometers and it is not a problem if I can't read every audio frame. Is it possible to, for each radio frame, connect the external analog mux to a different potentiometer and store the different results internally in different places e.g. by using some synchronized switching function?

/Tore

Hi Tore,

One way to store a variable within SigmaDSP is with a block that feeds back to itself. For example, you can use feedback around an ABCD comparator to build a "track-hold" to store levels in between refreshes. The circuit below uses two of these track-holds to independently control Left and Right volume with just one "input". Here the external mux and controls are simulated inside the SigmaDSP; of course this is where you would connect your external signals and mux.

Hope this helps,

Bob