Foot controller

[StaffanMelin]

So I am thinking of making a foot controller for the Haxo.

initial thoughts and ideas

• expression pedal for controlling brightness (filter cutoff)
• configurable
• add 4 buttons for switching sounds etc
• display? LEDs!

Making it

• adding a small MCU with Analog in to the Haxo (useful for other stuff too, ie interfacing): I am thinking about a XIAO (https://wiki.seeedstudio.com/Seeeduino-XIAO/) as it is super small, versatile, and I have one already
• pressure sensing: resistive film? pot with a return spring? bend resistor?
• put the MCU in the foot controller instead? Better to send digital than analog thru a wire to the RPi on the Haxo?
• use piezos for foot switches as they are prob more durable...?

Any thoughts?

[jcard0na]

Hi @StaffanMelin,

This sounds like a fun project. I would recommend also opening a discussion in https://github.com/cardonabits/haxo-hw/discussions where you might get feedback from more hardware-oriented folks.

My recommendation on hardware selection would be that it is easy to source. If you want people to contribute, the hardware should be cheap and widely available. Also, if you stay in Rust you will not introduce language barriers to those already familiar with haxo-rs.

So why not stay with a Raspberry Pi Zero? They are cheap, widely available, familiar to most haxophonists and small enough to fit on a foot pedal. In fact there are several guitar foot pedals that use it: 1 2 ... or even the RPI4 3

Looking forward to see what you come up with!

[StaffanMelin]

Thank you for your thoughts.

For this project I think an MCU as apposed to a SBC will be more suitable. I don't need (nor want) an OS and to fiddle with SD cards etc, and I want the built in ADCs of a MCU. So anything from an Arduino to a RP2040 sounds about right.

As well as being really cheap, the XIAO has 12 bit ADC resolution (and 11 GPIOs), and even a 10 bit DAC (CV out, right, for connecting to modular stuff, even though it is only 3.3V).

We'll see where I end up!

[jcard0na]

I see. In that case I would just ask you to consider an option that be programmed in Rust. I've been programming STM32s in Rust for some time now, and never missed my C/C++ days...
The STM32s have tons of variants, so you should be able to find the built-in peripherals you want for your project (https://www.st.com/content/st_com/en/stm32-mcu-product-selector.html).

[StaffanMelin]

I've never really understood what STMs are? :) Just a brand, licensing the ARM Cortex processors? But with good SW/lib support?

I've worked a lot with the Daisy Seed, a Cortex M7 with an audio codec, very fast for doing DSP: https://electro-smith.com/products/daisy-seed. There seems to be STM stuff in the toolchain...

But for the foot controller application, I don't need any more processing power than what an Arduino provides. No audio processing, that will all run on the RPi.

The Seeed XIAO SAMD21 is cheap with great io. It has a Cortex M0.

Rust is certainly an option, I'll promise to think about it! :)

[jcard0na]

Thank you!

[StaffanMelin]

So the prototype hardware is finished as a simple ... prototype! :)

It is powered by the inexpensive yet powerful Seeed Xiao (SAMD21 version), chosen because a) it has good connectivity b) I already had one. :)

I also had some pieces laying about from a previous controller project so I simply put them together and connected them up to the Xiao. Well, I had to replace the two pots on the mod and pitch wheel (that I salvaged from a broken keyboard in my common garbage room).

1. Xiao
2. Mod wheel, for LFO intensity etc
3. Pitch bend wheel (with a spring so it centers)
4. Distanse sensor (ultrasonic), it can measure the distanse from eg a foot with good precision. Filter cutoff?
5. Not connected yet, but it is a 4-channel DAC with 12 bits. I am going to use it to connect my haxo to my analog gear (pitch, control x 3), I will also add a gate out directly from the Xiao.
6. USB connection. I am going to connect the Xiao via USB (Serial) to the Haxo. I already have some C++ test code running on the Xiao and the laptop (which is going to be replaced by the Raspberry Pi connected to the Haxo).

Future plans include connecting a small OLED over I2C, as well as a simple analog button combo, so I can build a simple interface on the Xiao. Then the ports of the Xiao are all but taken.

All in all, pretty standard stuff, readily available.

I hope to have a working example this weekend. If I find it useful, I will add documentation and code (I will anyway! :) ).

I hope to be able to use the 2, 3 and 4 with my feet, we'll see. Whatever, the important thing is having some kind of analog input and get it to the Raspberry Pi on the haxo.

I call it the "Hexo"! :)

[Ekolide]

That's cool! How do you interface the Haxophone with the Xiao?

[StaffanMelin]

Thank you! :) I am using the USB-port on the XIAO and one on the Raspberry Pi (I am using a 4B so I have plenty). So it is serial (se point 6 above). I have a really simple protocol, sending comma separated integers, one for each "sub-controller" (wheel, ultrasonic sensor etc). Working fine!

I did some coding this weekend, building a sort of modulation matrix between the controller and the haxo. I hope to finish a test this week. :)