Questions about PWM output and A/D input 12 bit

#1

Hi , does anybody know the frequency from the PWM outputs ??
Than there are two 12 Bit outputs and a lot of 12 bit inputs inputs. What is the maximal frequency for input and also for output .
First , the max frequency for ADC 1_IN 0....14. Is it 44,1 Khz ??
Second low speed 12 BIT DA conversion- the max frequency ? .
Third the frequencyof the PWM output timer PA 6.,7 pb 0,1. I mean the timer clock.

This is very helpfull for a digital - analoge conversion - also for control voltages.

thanks
Greets
Andre'

#2

PWM output clock is set up to roughly 100Hz in firmware.
All GPIO ADC and DAC is setup to convert at 3kHz, (soft)synchronous with control rate.

In the future PWM should be set up in corresponding gpio/out/pwm objects, rather than in firmware, so you can choose different frequencies, I created issue #263 on github to keep track.
I believe GPIO ADC could also be setup in firmware to convert at 48kHz hardsynced to the audio clock (still, do not expect decent audio quality from those), but this is quite some more development work.

#3

Hi Johannes , uuhh 100 HZ is a little less. I am thinking about a combination of Axoloti oscillators and analog Filter unit. Three KHZ for the DAC is Ok but we have only two ...
This needs a few outputs , equal if PWM or Dac's. For the PWM minimum half audio frequency is need 20Khz
or better 40 khz to get a clean DC signal to control filters or route the ADSR from Axoloti direct to a PWM .
but ok .. next firmware. thanks for your answer. .
Greets
Andre'

PWM output pin frequency
#4

So far I have only made and used the GPIO PWM outs to control led dimmers and servo motors.

You could hack into firmware/axoloti_board.c if you want to test higher pwm frequencies.
For extra CV DAC channels I think adding an external SPI or I2C DAC is a better approach. There is a thread discussing such setup here: https://sebiik.github.io/community.axoloti.com.backup/t/gpio-i-o-example-dac-mcp4x22-spi/134

#5

I would like to use the pwm outputs to drive two analog meters to get some idea of levels in a patch while not connected to the computer. Should I get the current driven or the voltage driven meters and which ones can I set up with just a little padding circuit rather than active amplification?

#6

I believe those moving coil analog meters are essentially current sensitive and use a series resistor to measure voltage. The current sensitivity depends on the brand/model. One example is the Anders C360VU, which specifies 200 microA current for full scale deflection, more than sensitive enough to drive from a PWM output with a simple series resistor (~15kOhm).