Audio-to-DC for gpio/analog/in: range?

#1

Hi all,
I hope I can make my question clear enough, consider this my first community.axoloti.com test... smile
I made a circuitboard that converts an audio signal to a DC signal, so that it can be read by gpio/analog/in.
The output's "zero" is at 2.5v and a soundwave oscillates around that (presumably downwards to 0 and upwards to 5).
Now in the patcher, when I connect a [disp/dial p], it shows ~48.17 as midpoint, and the waveforms oscillate round that.
Why is the K-rate "sound wave" not oscillating around 32, between 0 and 64?
Is gpio range 5v or 3.3v?
gr,
Tim

#2

The analog range is 0 to 3.3V, that maps to 0-64 units.
2.5V*64/3.3V equals 48.48. It had been better to use 1.65V as midpoint.
I don't know the details of the circuit you made, this may be a small change. Perhaps supplying it 3.3V from VDDA rather than +5V?

It's a pity Arduino teaches the world to use 5V for everything, while 5V logic is uncommon these days. Axoloti is 3.3V for all GPIO.

#3

Hi Johannes,
Indeed, connecting to VDDA or VDD is what i needed to do, thanks!
Tim

#4

@johannes Is there any technical reason that a k-rate integer analog-In module could not be made? The ADC has 12 Bit resolution so 128 steps are far away from the "analog in" capabilities.

I ask because I Iike to use analog signals from a modular system +10/-10V (or 5/-5) reduced over an OPAMP attenuator to 0-3,3V so in this case 128 steps are a little bit to rough to read CV over a spread of 10V or in worst case 20V. K-Rate modules can handle this resolution due to their integer flavour. I'll not spend a lot of time into this to find out at the end that there is a technical reason why it is not made. wink

And a second questions: Do we have a 3,3 or 3V voltage reference somewhere on the board? (Or any other voltage reference I could use for an high precion OPAMP. (Without a voltage ref, a TN072 would do the job I think But then mapping CV notes is not very good.

#5

@johanes -> Some ansers I found here.

Euxoloti for axoloti (Eurorack Module)

I will take over the question to this thread. No answer needed.

Peter

This answers the most things I want to know smile

#6

@hesspet the VDDA pads are the 3.3V reference for the adc inside the microcontroller. If you desolder R1 (which is a ferrite) you can (and must) supply your own convertor reference voltage. Or you could supply your own voltage reference to one of the analog inputs to compensate for your reference.