Pretty much this is what the following code does. Put this data into JSON format and send it SoftSerial.

We setup a SoftSerial on pins 2,3 (Rx,Tx) and read a analog pin every five seconds. Put your Broker details (if you don’t have a broker you can use the defaults and click on connect, when ever UNO sends a new message it should appear here)įirst we will write program Arduino UNO to generate data periodically and send it on serial line to NodeMCU. You can view the data sent by the UNO on any MQTT client by subscribing to the topic “ /ic/nm/serialdata/uno/“, I also embedded MQTT client at the end of this blog, scroll down to see it. We will push the data received on serial line on “ /ic/nm/serialdata/uno/” channel/topic. Solution Approach: Connecting Arduino UNO with NodeMCU

mqtt broker , if you don’t have one you can use eclipse Paho broker for experimentation (host:, port : 1883, it is a free and open broker).

Arduino libraries : PubSubClient (if you haven’t already installed it, you can install it from Sketch->Include library->Manage Libraries).

setup your Arduino IDE to program NodeMCU.

I am not showing the level converter in the circuit diagrams, if you want to use refer this post for connection diagram) (Note: most of the nodemcu devices work fine without a level converter.

you would also need a 5v to 3v3 level converter to convert the UART signal levels.

you need to have UNO and ESP8266/NodeMCU.

To send data from Arduino UNO to ESP8266 we will use UART. Since Arduino UNO doesn’t have any network capabilities we need to device that can do networking for us, whats better than ESP8266. What we are trying to achieve is simple, Arduino UNO generates some data (may be sensor readings) and we want to send that to cloud (in this case MQTT broker). That project uses lua to program the NodeMCU devices, to make it simple to use I will use Arduino IDE to program both the devices in this post. We have already seen how to connect Arduino UNO with NodeMCU/ESP8266 over UART and send data to MQTT broker here.

Esp8266 arduino uno r3 datasheet