Audio Mixer (LBB)

Audio Mixer – Lab Bench Board
(Version 1.0)

Introduction

The main goal with this project is to introduce students to the design, simulation and build circuits that use operational amplifiers and apply concepts learned during a circuits class (e.g. voltage dividers, inverters, summers, etc).

Design Stage

We will be using the UA741 for the op amps and the HiLetgo M28 Wireless Bluetooth receiver board.

Simulations (Falstad)

(Link)

Simulations (LTSpice)

(LTSpice Audio Mixer File)
(LTSpice Pot File)

Prototype Stage

Testing setup

Download a function generator app in your phone
- The Oscillator (for iPhone) Free
- Function Generator (for Android) Free
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

Sine + Sine Waveform

Left Channel – Sine Wave (450 Hz)

Right Channel – Sine Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

Sine + Triangle Waveform

Left Channel – Sine Wave (450 Hz)

Right Channel – Triangle Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

Square + Triangle Waveform

Left Channel – Square Wave (450 Hz)

Right Channel – Triangle Wave (550 Hz)

Mixed Signal

Waveform Summer Validation (Desmos)

(Link)

PCB Design

Schematics (Zoom)

Layout (Zoom)

3D Rendering

Interactive BOM (Zoom)

Assemble Stage

The boards were manufactured by JLCPCB.

Assembled in house.

Testing Stage (with PCB)

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.