Audio Mixer (LBB)

Audio Mixer – Lab Bench Board
(Version 1.0)

The idea is to connect an audio Bluetooth module into an audio mixer with the goal to control the left and right channel gain and overall volume.

Simulations (Falstad)

(Link)

Simulations (LTSpice)

(LTSpice Audio Mixer File)
(LTSpice Pot File)

Protoboard

After getting an idea on the desired functionalities, input and outputs, the circuit was built on protoboard.

Testing setup

  • Download a function generator app in your phone
  • The Audio Mixer LBB output was connected to an oscilloscope and tested with different types of waveforms.
  • Oscilloscope: Keysight MSOX3012T – 100 MHz @ 5 GSa/s

Left Channel – Sine Wave (450 Hz)

Right Channel – Sine Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

Left Channel – Sine Wave (450 Hz)

Right Channel – Triangle Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

Left Channel – Square Wave (450 Hz)

Right Channel – Triangle Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

3D Model

During design stage, Fusion 360 and KiCad were used to model the board and get an idea on how the board would look like.

Note: Unfortunately, I was not able to find a step model for the HiLetGo Bluetooth Module M28.

Inputs

  • 2 gain knobs
  • 1 volume knob
  • Audio input (Bluetooth module)

Outputs

  • Audio output (3.5 mm Jack)

PCB

Schematics

Interactive HTML BOM

The boards were manufactured by JLCPCB.

Assembled in house.

Testing setup

  • The Audio Mixer LBB output was connected to an oscilloscope and tested with different types of waveforms.
  • Oscilloscope: Keysight MSOX3012T – 100 MHz @ 5 GSa/s
  • The Oscillator App for Iphones or the Function Generator App for Androids can be used to generate waveforms and transmit that information over Bluetooth to the Audio Mixer LBB.

Left Channel – Square Wave (450 Hz)

Right Channel – Square Wave (550 Hz)

Mixed Signal

Left Channel – Sine Wave (450 Hz)

Right Channel – Triangle Wave (550 Hz)

Mixed Signal

Left Channel – Square Wave (450 Hz)

Right Channel – Square Wave (550 Hz)

Mixed Signal

Sound Test 1

Audio Mixer Duo – Lab Bench Board
(Version 1.0)

Soon…

PCB

The boards were manufactured by JLCPCB.

Assembled in house.

Sound Test 1

Leave a Reply

Your email address will not be published.