How to get a maximum of knobs on a axoloti core?

[mtyas]

After making my first few sound boxes with axoloti, I was rapidly in search of having a maximum amount of knobs at my disposal.
I’ve used the midi standard (by using off the shelf midi controllers, or by making my own using a teensy board or the Touch Board by bare conductive) but I would really like to use the 12 bit resolution that the axoloti offers.
I’ve tried understanding multiplexing by following these forum threads :
for ADC (inputs) :

[GPIO I/O] Example ADC MCP3208 & SPI

Hi everyone, this example should show, how a MCP3208 can be used to read eight analog sources. The MCP3208 is connected to axoloti SPI port. This ADC method is much faster then the 4051 method and the MCP3208 has an input protection. Each ADC channel has a 12bit resolution and is compared to the VREF voltage. VREF should be in a range of 0,25V to VDD and decoupled/stabilized by a 100nF capacitor and min. 10uF polarized capacitor (not shown in the wiring picture). If you want to use more then one…

[GPIO I/O] Example 4051 de/multiplexer reads 8 analog sources

Hi everyone, here is a short example for a 4051 de/multiplexer. The 4051 can be used for extra 8 analog outputs or inputs. The Y0-7 pins are choosen by HIGH/LOW state of the S0-2 pins. It's not the fastest way to expand the analog input or output, but the IC are very cheap and I own a lot of them [sweat_smile] It's good thing to decouple the analog inputs and VCC with a 100n capacitor. A MCP3008 or MCP3208 SPI is much faster and has an input protection build in. An examples for this IC will b…

for DAC (outputs) :

[GPIO I/O] Example DAC MCP4x22 & SPI

Hi, motivated by a request of cereyanlimusiki at my "Euxoloti for axoloti (Eurorack Module)" Thread, I tried some MCP4922 and MCP4822 DACs to generate some CV outs. Vrefs and VCC should be decoupled by 100n capacitors. Don't forget, the axoloti core has two dac outs (PA4/PA5). Download Patch: spi mcp4x22.axp (4.0 KB) [image] Schematic: [image]

But I get very easily confused my the amount of multiplexer chips available and the ways to assign them in the patching software.

So here are my questions :

What is an easy way to get a maximum (and what is the limit) of analog inputs and outputs from an axoloti core board ?

Is there not a way to use a teensy board (that offers 21 analog inputs) and communicate with axoloti via serial port (instead of reducing to 8bit and converting to midi protocol) ?

Is there any other way ?

[kassu]

Probably all the suggestions you give are good solutions, but here is just another idea to add to the mix:

you could use "high res" midi controllers. The idea is to send data on 2 midi CC's, one for the 7 MSB and one for the 7 LSB, giving 14 bit resolution in total. The object "midi/in/cc hr ii" can read these, and it should be easy to send them with the teensy if you are already using those.

Edit: the feasible maximum number of knobs is (a bit less than) 64, as you need 2 CCs for each knob. Another way that is almost the same is using midi NRPNs (non-registered parameter numbers), that allows for 2^14 different parameters, but needs up to 4 midi messages for each parameter change.

[paul]

It's a good solution to out source the control handling and send the final results via MIDI to Axoloti. It saves resources for more sound processing.
A 4051 is just 8 channel analog router which can be control by 3 logic input (s0, s1, s2). check datasheet page 5 for detailed routing: 4051 Datasheet

I don't know how much inputs you need, but you can check out the ainser64 PCB from ucapps. It uses one mcp3208 and a 74hc595 to control and read (12bit) 8x 4051. With this module you can hook up 64 analog sources. I can't get it working with shared CS pins but with split CS pins.

An other flexible and extendable solution will be the e.g. MIDIO128 V3 project from ucapps.

[deef]

hey @mtyas!
around 2 years passed - how did you resolve this question for you?
because I wonder about the same thing now.
(btw thank you for your long axoloti patching videos (sampler, granular, delay-fun).
I watched them all a couple of times & learned a lot.