ESP32-LyraT-Mini V1.2 Hardware Reference

This guide provides functional descriptions, configuration options for ESP32-LyraT-Mini V1.2 audio development board. As an introduction to functionality and using the LyraT, please see ESP32-LyraT-Mini V1.2 Getting Started Guide.


The ESP32-LyraT is a hardware platform designed for the dual-core ESP32 audio applications, e.g., Wi-Fi or BT audio speakers, speech-based remote controllers, connected smart-home appliances with one or more audio functionality, etc.

The block diagram below presents main components of the ESP32-LyraT-Mini.

ESP32-LyraT-Mini V1.2 Electrical Block Diagram

ESP32-LyraT-Mini V1.2 Electrical Block Diagram

Functional Description

The following list and figure describe key components, interfaces and controls of the ESP32-LyraT-Mini board. The list provides description starting from the picture’s top right corner and going clockwise.

MicroSD Card
The development board supports a MicroSD card in SPI/1-bit modes, and can store or play audio files in the MicroSD card. See MicroSD Card for pinout details.
On-board microphone connected to AINRP/AINRP of the Audio ADC Chip.
System LEDs
Two general purpose LEDs (green and red) controlled by ESP32-WROVER-B Module to indicate certain operation states of the audio application using dedicated API.
Audio Codec Chip
The audio codec chip, ES8311, is a low power mono audio codec. It consists of 1-channel ADC, 1-channel DAC, low noise pre-amplifier, headphone driver, digital sound effects, analog mixing and gain functions. It is interfaced with ESP32-WROVER-B Module over I2S and I2C buses to provide audio processing in hardware independently from the audio application.
Audio Output
Output socket to connect headphones with a 3.5 mm stereo jack. One of the socket’s terminals is wired to ESP32 to provide jack insertion detection.
Audio ADC Chip
The audio codec chip, ES7243, is a low power multi-bit delta-sigma audio ADC and DAC. In this board this chip is used as the microphone interface.
PA Chip
A power amplifier used to amplify the audio signal from the Audio Codec Chip for driving the 4-ohm speaker.
Speaker Output
Output socket to connect 4 ohm speaker. The pins have a standard 2.54 mm / 0.1” pitch.
Audio Function Press Keys
Six press keys labeled Rec, Mode, Play, Set, Vol- and Vol+. They are routed to ESP32-WROVER-B Module and intended for development and testing of a UI for audio applications using dedicated API.
ESP32 LyraT-Mini V1.2 Board Layout

ESP32 LyraT-Mini V1.2 Board Layout

Boot/Reset Press Keys
Boot: holding down the Boot button and momentarily pressing the Reset button initiates the firmware upload mode. Then user can upload firmware through the serial port. Reset: pressing this button alone resets the system.
Automatic Upload
A simple two transistor circuit to put ESP32 into firmware upload mode depending on the status of UART DTR and RTS signals. The signals are controlled by an external application to upload the firmware over the USB-UART interface.
Functions as the communication interface between a PC and the ESP32 module.
USB-UART Bridge Chip
A single chip USB-UART bridge CP2102N provides up to 3 Mbps transfers rates.
Standby / Charging LEDs
The Standby green LED indicates that power has been applied to the USB Power Port. The Charging red LED indicates that a battery connected to the Battery Socket is being charged.
Battery Socket

Two pins socket to connect a single cell Li-ion battery.


Please verify if polarity on the battery plug matches polarity of the socket as marked on the board’s soldermask besides the socket.

Battery Charger Chip
Constant current and constant voltage linear charger for single cell lithium-ion batteries AP5056. Used for charging of a battery connected to the Battery Socket over the USB Power Port.
Power On Switch

Power on/off knob: toggling it to the top powers the board on; toggling it to the down powers the board off.


The Power On Switch does not affect / disconnect the Li-ion battery charging. More information, you can refer to ESP32-LyraT-Mini V1.2 schematic (PDF).

Power Supervisor
Provides EN signal to enable ESP32 once power supply voltage stabilizes.
Power On LED
Red LED indicating that Power On Switch is turned on.
The ESP32-WROVER-B module contains ESP32 chip to provide Wi-Fi / BT connectivity and data processing power as well as integrates 64 Mbit SPI flash and 64 Mbit PSRAM for flexible data storage.
UART Test Point
Serial port: provides access to the serial TX/RX signals between ESP32-WROVER-B Module and USB-UART Bridge Chip. See UART Test Point for pinout details.
JTAG Test Point
Provides access to the JTAG interface of ESP32-WROVER-B Module. It may be used for debugging, application upload, as well as implementing several other functions, e.g., Application Level Tracing. See JTAG Test Point for pinout details.

Allocation of ESP32 Pins to Test Points

This section describes allocation of test points available on the ESP32-LyraT-Mini board.

The test points are bare through hole solder pads and have standard 2.54 mm / 0.1 inch pitch. User may need to populate them with pin headers or sockets for easy connection of external hardware.

JTAG Test Point

. ESP32 Pin JTAG Signal

UART Test Point

. ESP32 Pin Pin Description
4 n/a 3.3 V

MicroSD Card

Implemented on this board MicoSD card interface operates in SPI/1-bit mode. The board is able to support SPI/4-b it mode after populating couple of additional components on locations reserved on the PCB. See ESP32-LyraT-Mini V1.2 schematic (PDF) for additional information. Not populated components are marked (NC) on the schematic.

. ESP32 Pin MicroSD Signal

GPIO Allocation Summary

The table below provides allocation of GPIOs exposed on terminals of ESP32-WROVER-B Module to control specific components or functions of the board.

Pin 1 Pin Name ES8311 ES7243 Keys MicroSD Other
3 EN     EN_KEY    
4 S_VP   I2S_DATA      
5 S_VN     REC, MODE, PLAY, SET, VOL-, VOL+    
6 IO34       CD  
7 IO35 I2S0_ASDOUT        
8 IO32   I2S1_SCLK      
9 IO33   I2S1_LRCK      
10 IO25 I2S0_LRCK        
11 IO26 I2S0_DSDIN        
12 IO27         Blue_LED
13 IO14       CLK  
14 IO12       NC (DATA2)  
16 IO13       NC (DATA3)  
17 SD2          
18 SD3          
19 CMD          
20 CLK          
21 SD0          
22 SD1          
23 IO15       CMD  
24 IO2     IO2_KEY DATA0  
25 IO0 I2S0_MCLK I2S1_MCLK IO0_KEY    
26 IO4       NC (DATA1)  
27 NC (IO16)          
28 NC (IO17)          
29 IO5 I2S0_SCLK        
30 IO18 I2C_SDA I2C_SDA      
31 IO19         PJ_DET 2
33 IO21         PA_CTRL 3
34 RXD0         RXD0 4
35 TXD0         TXD0 4
36 IO22         Green_LED
37 IO23 I2C_SCK I2C_SCL      
  1. Pin - ESP32-WROVER-B module pin number, GND and power supply pins are not listed
  2. PJ_DET - phone jack insertion detect signal
  3. PA_CTRL - NS4150 power amplifier chip control signal
  4. RXD0, TXD0 - serial communication signals connected to TXD and RXD pins of CP2102N USB-UART bridge
  5. NC - not connected

Notes on Power Distribution

The ESP32-LyraT-Mini board provides some basic features to isolate noise from digital components by providing separate power distribution for audio and digital subsystems.

Power Supply over USB and from Battery

The main power supply is 5V and provided by a USB. The secondary power supply is 3.7V and provided by an optional battery. The USB power itself is fed with a dedicated cable, separate from a USB cable used for an application upload. To further reduce noise from the USB, the battery may be used instead of the USB.

ESP32-LyraT-Mini V1.2 - Dedicated USB Power Supply Socket

ESP32-LyraT-Mini V1.2 - Dedicated USB Power Supply Socket

ESP32-LyraT-Mini V1.2 - Power Supply from a Battery

ESP32-LyraT-Mini V1.2 - Power Supply from a Battery

Independent Audio and Digital Power Supply

The board features independent power supplies to the audio components and ESP32 module. This should reduce noise in the audio signal from digital components and improve overall performance of the components.

ESP32-LyraT-Mini V1.2 - Digital Power Supply

ESP32-LyraT-Mini V1.2 - Digital Power Supply

ESP32-LyraT-Mini V1.2 - Audio Power Supply

ESP32-LyraT-Mini V1.2 - Audio Power Supply

Selecting of the Audio Output

The board provides a mono audio output signal on pins OUTN and OUTP of the ES8311 codec chip. The signal is routed to two outputs:

  • power amplifier (PA) to drive an external speaker,
  • phone jack socket to drive external headphones.

The board design assumes that selection between one of these outputs is implemented in software, as opposed to using traditional mechanical contacts in a phone jack socket, that would disconnect the speaker once a headphone jack is inserted.

Two digital IO signals are provided to implement selection between the speaker and the headphones:

  • PJ_DET - digital input signal to o detect when a headphone jack is inserted,
  • PA_CTRL - digital output signal to enable or disable the amplifier IC.

The application running on ESP32 may then enable of disable the PA with PA_CTRL basing on status of PJ_DET. Please see GPIO Allocation Summary for specific GPIO numbers allocated to these signals.