Heltec WiFi LoRa 32 V2 boards

Support for Heltec WiFi LoRa 32 V2 boards. More...

Detailed Description

Support for Heltec WiFi LoRa 32 V2 boards.

Author

Gunar Schorcht gunar.nosp@m.@sch.nosp@m.orcht.nosp@m..net

Heltec WiFi LoRa 32 V2

Table of Contents

1. Overview
2. Hardware
   1. MCU
   2. Board Configuration
   3. Board Pinout
   4. Using the OLED Display
   5. Optional Hardware Configurations
3. Flashing the Device

Overview

Heltec WiFi LoRa 32 V2 is an ESP32 development board with 8 MB Flash that uses the EPS32 chip directly. It integrates

• a SemTech SX1276 or SX1278 for LoRaWAN communication and
• a SSD1306 0.96-inch 128x64 OLED display connected via I2C.

Since the board is open source hardware, a number of clones are available.

Heltec WiFi Lora 32 V2

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Hardware

This section describes

• the MCU,
• the default board configuration,
• optional hardware configurations,
• the board pinout.

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MCU

Most features of the board are provided by the ESP32 SoC. For detailed information about the ESP32, see section MCU ESP32.

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Board Configuration

Heltec WiFi LoRa 32 V2 has the following on-board components:

• SemTech SX1278 or SX1276 for LoRaWAN communication
• SSD1306 0.96-inch 128x64 OLED display connected via I2C
• external 32.768 kHz crystal for RTC

There are two hardware versions of the board:

• SemTech SX1278 for LoRaWAN communication in the 433 MHz band
• SemTech SX1276 for LoRaWAN communication in the 868/915 MHz band

Since many GPIOs are broken out, they can be used for different purposes in different applications. For flexibility, some GPIOs might be listed in various peripheral configurations. For example, GPIO0 is used in the ADC channel definition ADC_GPIOS and the PWM channel definition PWM0_GPIOS.

This is possible because GPIOs are only used for a specific peripheral interface when

• the corresponding peripheral module is used, e.g., module periph_i2c, or
• a corresponding init function is called e.g., adc_init, dac_init and pwm_init, or
• the corresponding peripheral interface is used for the first time, e.g., spi_acquire.

That is, the purpose for which a GPIO is actually used depends on which module or function is used first.

Note

GPIOs 19, 4, 5, 14, 15, 16, 18, 32, 33, 34, 35, 21, 26, and 27 are used for board control functions and should not be used for other purposes unless you exactly know what you are doing.

The following table shows the default board configuration, which is sorted according to the defined functionality of GPIOs. This configuration can be overridden by application-specific configurations.

Function	GPIOs	Remarks	Configuration
BTN0	GPIO0	low active
LED0	GPIO25	high active
ADC	GPIO36, GPIO39, GPIO37, GPIO38, GPIO0, GPIO2, GPIO12, GPIO13, GPIO4, GPIO15		ADC Channels
DAC			DAC Channels
PWM_DEV(0)	GPIO25, GPIO0, GPIO2, GPIO17		PWM Channels
PWM_DEV(1)	GPIO22, GPIO23		PWM Channels
I2C_DEV(0):SDA	GPIO4		I2C Interfaces
I2C_DEV(0):SCL	GPIO15	I2C_SPEED_FAST is used	I2C Interfaces
SPI_DEV(0):CLK	GPIO5	VSPI is used	SPI Interfaces
SPI_DEV(0):MISO	GPIO19	VSPI is used	SPI Interfaces
SPI_DEV(0):MOSI	GPIO27	VSPI is used	SPI Interfaces
SPI_DEV(0):CS0	GPIO18	VSPI is used	SPI Interfaces
UART_DEV(0):TxD	GPIO1	Console (configuration is fixed)	UART interfaces
UART_DEV(0):RxD	GPIO3	Console (configuration is fixed)	UART interfaces
UART_DEV(1):TxD	GPIO10	not available in qout and qio flash mode	UART interfaces
UART_DEV(1):RxD	GPIO9	not available in qout and qio flash mode	UART interfaces
OLED RESET	GPIO16

Note

• The configuration of ADC channels contains all ESP32 GPIOs that can be used as ADC channels.
• GPIO9 and GPIO10 can only be used in dout and dio flash modes.

For detailed information about the configuration of ESP32 boards, see section Common Peripherals.

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Using the OLED Display

The 0.96-inch OLED display with 128x64 pixels uses the widely used SSD1306 controller. It is connected via I2C_DEV(0). It can be used with the pkg/u8g2 package. For this purpose, the pkg/u8g2 package has to be used in the application Makefile

USEPKG += u8g2

and function u8g2_Setup_ssd1306_i2c_128x64_noname_f has to be called to setup the right driver, for example:

#include "u8g2.h"
#include "u8x8_riotos.h"
 
#define SSD1306_I2C_ADDR    (0x3c)
 
u8x8_riotos_t user_data = {
    .device_index = I2C_DEV(0),
    .pin_cs = GPIO_UNDEF,
    .pin_dc = GPIO_UNDEF,
    .pin_reset = GPIO16,
};
 
u8g2_Setup_ssd1306_i2c_128x64_noname_f(&u8g2, U8G2_R0,
                                       u8x8_byte_hw_i2c_riotos,
                                       u8x8_gpio_and_delay_riotos);
u8g2_SetUserPtr(&u8g2, &user_data);
u8g2_SetI2CAddress(&u8g2, SSD1306_I2C_ADDR);
u8g2_InitDisplay(&u8g2);
u8g2_SetPowerSave(&u8g2, 0);

The tests/pkg/u8g2 test application is a good example of how to use the pkg/u8g2 package. It can be compiled for the board with the following command:

TEST_OUTPUT=4 TEST_I2C=0 TEST_ADDR=0x3c TEST_PIN_RESET=GPIO16 \
TEST_DISPLAY=u8g2_Setup_ssd1306_i2c_128x64_noname_f \
BOARD=esp32-heltec-lora32-v2 make -C tests/pkg/u8g2/ flash

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Optional Hardware Configurations

MRF24J40-based IEEE 802.15.4 radio modules and ENC28J60-based Ethernet network interface modules have been tested with the board. You could use the following code in your application-specific configuration to use such modules:

#ifdef BOARD_ESP32_HELTEC_LORA32_V2
 
#if MODULE_MRF24J40
#define MRF24J40_PARAM_CS       GPIO12      /* MRF24J40 CS signal    */
#define MRF24J40_PARAM_RESET    GPIO22      /* MRF24J40 RESET signal */
#define MRF24J40_PARAM_INT      GPIO23      /* MRF24J40 INT signal   */
#endif
 
#if MODULE_ENC28J80
#define ENC28J80_PARAM_CS       GPIO12      /* ENC28J80 CS signal    */
#define ENC28J80_PARAM_RESET    GPIO22      /* ENC28J80 RESET signal */
#define ENC28J80_PARAM_INT      GPIO23      /* ENC28J80 INT signal   */
#endif
 
#endif

For other parameters, the default values defined by the drivers can be used.

Note

The RESET signal of MRF24J40 and ENC28J60 based modules can also be connected to the RST pin of the board (see pinout) to keep the configured GPIO free for other purposes.

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Board Pinout

The following figure shows the pinout of the defined default configuration for Heltec WiFi LoRa 32 V2 boards. The light green GPIOs are not used by configured on-board hardware components and can be used for any purpose. However, if optional off-board hardware modules are used, these GPIOs may also be occupied, see section Board Configuration for more information.

The corresponding board schematics can be found here for SX1276 version and here for SX1278 version.

WiFi LoRa 32 V2 Pintout Diagram

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Flashing the Device

Flashing RIOT is quite easy. The board has a Micro-USB connector with reset/boot/flash logic. Just connect the board to your host computer and type using the programming port:

make flash BOARD=esp32-heltec-lora32-v2 ...

For detailed information about ESP32 as well as configuring and compiling RIOT for ESP32 boards, see RIOT-OS on ESP32 SoC Series Boards.

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Files
file	arduino_iomap.h
	Mapping from MCU pins to Arduino pins.
file	board.h
	Board specific definitions for Heltec WiFi LoRa 32 V2 board.
file	gpio_params.h
	Board specific configuration of direct mapped GPIOs.
file	periph_conf.h
	Peripheral MCU configuration for Heltec WiFi LoRa 32 V2 board.