This library provides an object that can be used just like Serial for printing logs, however the text sent with print() etc. is published on a MQTT broker instead of printing over the Serial console. This comes in handy when working with devices like the ESP8266/ESP32 that are connected over WiFi. I use it for debugging my robots that are based on ESP32.

The library uses PubSubClient for sending the MQTT messages.

When no MQTT connection is available, the MqttLogger object behaves just like Serial, i.e. your print() text is shown on the Serial console. The logger offers the following modes that can be passed as the third argument to the constructor when instantiating the object:

• MqttLoggerMode::MqttAndSerialFallback - this is the default mode. print() will publish to the MQTT server, and only when no MQTT connection is available Serial will be used. If you print() messages before the MQTT connection is established, these messages will be sent to the Serial console.
• MqttLoggerMode::MqttOnly - no output on Serial. Beware: when no connection is available, no output is produced
• MqttLoggerMode::SerialOnly - no messages are sent to the MQTT server. With this configuration MqttLogger can be used as a substitute for logging with Serial.
• MqttLoggerMode::MqttAndSerial - messages are sent both to the MQTT server and to the Serial console.

See directory examples. Currently there is only one example in directory esp32.

In this directory, rename the file wifi_secrets.h.txt to wifi_secrets.h and edit the file. Enter your WiFi ssid and password, the example uses this include file to set up your WiFi connection.

You'll need a MQTT broker to publish your messages to, I use Mosquitto installed locally on my laptop. You can also use a free public service like test.mosquitto.org or broker.hivemq.com, but this makes logging slower (the messages have to be sent to and then downloaded from the online service). Also, make sure no private information is logged!

The broker url is defined by the constant mqtt_server in the example, use localhost if you have a local install as recommended.

For checking the mqtt logs events you'll use a MQTT client. The Mosquitto client can be invoked in a terminal like

mosquitto_sub -h localhost -t mqttlogger/log

but any other mqtt client will do (on Android try MQTT Dash, hivemq has a online version at (https://www.hivemq.com/demos/websocket-client/).

All devices that work with the PubSubClient should work with this libary, including:

• Arduino Ethernet
• Arduino Ethernet Shield
• Arduino YUN – use the included YunClient in place of EthernetClient, and be sure to do a Bridge.begin() first
• Arduino WiFi Shield - if you want to send packets > 90 bytes with this shield, enable the MQTT_MAX_TRANSFER_SIZE define in PubSubClient.h.
• Sparkfun WiFly Shield – library
• TI CC3000 WiFi - library
• Intel Galileo/Edison
• ESP8266
• ESP32

This code is released under the MIT License.