UHER Akustomat F411

UHER Akustomat F411 - first iteration

Overview
Iterations
Components
- Potentiometer
- LED Button
Pull-up and pull-down resistors
References

Overview

This is an old UHER Akustomat F411¹, that has been stripped of it's original internals² and replaced with:

ESP32 C3 SuperMini
Potentiometer for volume control, using ADC³ on the ESP32.
Button with an LED⁴, brightness of the LED is set with PWM⁵ according to the volume level.

I use this device to give physical control to an OwnTone output. The current iteration uses an ESP32 C3 SuperMini running ESPHome.

Iterations

This (simple) project has gone through multiple iterations and improvements:

ESP8266 NodeMCU with a potentiometer, later added a single LED diode

This was limited by the ESP8266 only having a single ADC, and lacks hardware PWM for LEDs. The ESP8266 I was using was also a dev board with pre-soldered pins that made it more bulky that it needed to be.
ESP32 S2 Mini with a potentiometer and LED button.

The internal wiring was still a mess, but switching to an ESP32 added hardware PWM for the LED with ESP32 LEDC output⁵.
ESP32 C3 SuperMini (current iteratation) with potentiometer and LED button where the brightness of the LED follows the volume level.

The wiring on this iteration is pretty clean. The biggest hurdle to that was that ESP32 C3 SuperMini only has one GND pin, and this project currently has 3x GND connections. Was able to structure two wireboards (that has inter-connected pin holes) and use 2.54mm JST connectors to make a relatively clean design.

The next iteration should be a custom designed PCB that eliminates the need for internal wiring completely.

Components

Pull-up and pull-down resistors

Either connect the the switch pins from a GPIO to GND with the internal pull-up resistor enabled or from from a GPIO to 3V3 with internal pull-down resistor enabled.

It is preferable to connect the switch between a GPIO and GND using pull-up resistors so that you don't have $3.3 V$ wires running away from the board where they could short to ground by accident and fry something.

binary_sensor:
  - platform: gpio
    id: gpio_button_s
    name: "UHER Akustomat F411 S"
    pin:
      number: "${binary_sensor_gpio}"
      inverted: true
      mode:
        input: true
        pullup: true
        pulldown: false
    publish_initial_state: true

When the button is pressed, the circuit is pulled LOW so we need to configure the pin with inverted enabled.

Schematic showing the difference between pull-up and pull-down resistors

Schematic by tom_l on Home Assistant forum¹⁰.

A pull-up resistor sits between GPIO and $V DD$ /3V3 and "pulls up to positive", while a pull-down resistor sits between GPIO and GND and "pulls down to negative" instead. The internal pull-up/pull-down resistors on the ESP32 does this internally on the board.