esp8266_mqtt_uart_bridge

esp8266 mqtt uart bridge.

Convert from UART output to MQTT publish.
Convert from MQTT subscribe to UART input.

Monitoring

You can monitor ESP8266 using Serial1.
Serial1 outputs to GPIO2

How to disable ESP8266 boot messages

ESP8266 boot rom writes a log to the UART when booting like this:

ets Jan  8 2014,rst cause 1, boot mode:(3,7)

load 0x40100000, len 24236, room 16
tail 12
chksum 0xb7
ho 0 tail 12 room 4
load 0x3ffe8000, len 3008, room 12
tail 4
chksum 0x2c
load 0x3ffe8bc0, len 4816, room 4
tail 12
chksum 0x46
csum 0x46

This message can cause unexpected trouble.

Swap UART

UART can be swapped by adding the following one line:

Serial.swap();

TX / RX changes to the following when UART is swapped.

GPIO15(TXD)   --- RX
GPIO13(RXD)   --- TX

The boot message does not reach RX port of other side.
However, since GPIO15 is a pin that determines the boot mode, ESP8266 does not start.
This method cannot be used.

Add a circuit

If the following circuit is added, All message does not reach RX port of other side.
I used 1N5819 Schottky Barrier Plastic Rectifier.

To start transmission, set the GPIO polarity to OUTPUT and the level to LOW.

pinMode(GPIO, OUTPUT);
digitalWrite(GPIO, LOW);
Serial.begin(115200);

NOTE:GPIO15 is pulled down and cannot be used for this.

MQTT to UART

You need to adjust the following environment.

#define MQTT_SERVER "broker.emqx.io"
IP of MQTT Broker
#define MQTT_PORT 1883
Port of MQTT Broker
#define MQTT_TOPIC "/esp-bridge"
Subscribe topic
#define MQTT_WILL_TOPIC "/esp-bridge"
Will topic
#define MQTT_WILL_MSG "I am leaving..."
Will message
#define UART_BAUDRATE 115200
UART boudrate
const char* ssid = "SSID of Your AP";
SSID of your Access Point
const char* password = "PASSWORD of Your AP";
Password of your Access Point

Publish using mosquitto-clients

$ mosquitto_pub -h broker.emqx.io -p 1883 -t "/esp-bridge" -m "Hello World"

UART to MQTT