ESP-NOW with OLED Display: Wireless Communication and Real-Time Data Monitoring

ESP-NOW is a powerful wireless communication protocol developed by Espressif that enables fast, low-power, connectionless data exchange between ESP32 and ESP8266 devices. When combined with an OLED display, ESP-NOW becomes even more useful for real-time monitoring of sensor data, device status, and control signals.

In this article, we will explore how to use ESP-NOW with OLED Display, its working principle, practical implementation, example projects, and step-by-step coding approach.

What is ESP-NOW?

ESP-NOW is a proprietary protocol created by Espressif that allows multiple ESP devices to communicate directly without the need for Wi-Fi infrastructure such as routers or internet connectivity.

Key Features of ESP-NOW

• Peer-to-peer wireless communication
• Works without Wi-Fi network
• Very low latency
• Low power consumption
• Supports encrypted communication
• Ideal for IoT and Wireless Sensor Networks (WSN)

Read This: ESP-NOW Protocol: A Complete Guide for ESP32 and ESP8266

Why Use OLED Display with ESP-NOW?

An OLED display provides a visual interface to show the received data wirelessly via ESP-NOW. Instead of sending data to cloud dashboards, you can instantly display:

• Temperature and humidity
• Button press status
• ADC readings
• Battery voltage
• Debug messages

This is extremely helpful in offline environments like factories, farms, or home automation systems.

How ESP-NOW Works

ESP-NOW communication works using MAC addresses. Devices are paired as:

• Sender (Transmitter)
• Receiver

The sender broadcasts structured data packets, and the receiver processes them and performs actions such as displaying information on OLED.

Hardware Components Required

For Sender Node

• ESP32 / ESP8266 board
• Sensor (DHT11, BMP280, etc.)
• Power supply

For Receiver with OLED

• ESP32 (recommended)
• 0.96 inch I2C OLED Display (SSD1306)
• Connecting wires

OLED Display Basics

Most IoT OLED displays use:

• I2C Interface
• SSD1306 Driver
• 128×64 resolution

I2C Pins

ESP-NOW with OLED Display Architecture

The complete system workflow looks like this:

1. Sensor data collected by Sender ESP
2. Data transmitted via ESP-NOW
3. Receiver ESP gets packet
4. OLED display updates in real time

Programming Environment

You can program using:

• Arduino IDE
• Thonny MicroPython IDE
• PlatformIO

But here we will focus on Arduino-based implementation as it is more common for ESP-NOW.

Required Arduino Libraries

Install the following libraries:

• Adafruit SSD1306
• Adafruit GFX
• espnow (built-in for ESP32 core)

Make sure you have the latest ESP32 board package installed.

Implementation Example

Now let us implement a simple project where an ESP32 sends temperature data and another ESP32 displays it on OLED.

Step 1: Get MAC Address of Receiver

Upload this sketch to OLED receiver ESP32:

#include "WiFi.h"

void setup(){
  Serial.begin(115200);
  WiFi.mode(WIFI_MODE_STA);
  Serial.println(WiFi.macAddress());
}

void loop(){}

Note down the printed MAC address.

Step 2: Sender Code

Data Structure

We create a structure to send data:

typedef struct struct_message {
  float temperature;
  float humidity;
} struct_message;

Complete Sender Sketch

#include <esp_now.h>
#include <WiFi.h>

struct_message myData;

uint8_t receiverAddress[] = {0x24,0x6F,0x28,0xAA,0xBB,0xCC};

void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("Send Status: ");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Success" : "Fail");
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);

  esp_now_init();

  esp_now_register_send_cb(OnDataSent);

  esp_now_peer_info_t peerInfo;
  memcpy(peerInfo.peer_addr, receiverAddress, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;

  esp_now_add_peer(&peerInfo);

  myData.temperature = 25.6;
  myData.humidity = 60.3;

  esp_now_send(receiverAddress, (uint8_t *) &myData, sizeof(myData));
}

void loop() {}

Step 3: OLED Receiver Code

Complete Sketch

#include <esp_now.h>
#include <WiFi.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

struct_message incomingData;

void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&incomingData, incomingData, sizeof(incomingData));
  updateOLED();
}

void updateOLED(){
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);

  display.setCursor(0,10);
  display.print("Temp: ");
  display.print(incomingData.temperature);
  display.println(" C");

  display.setCursor(0,30);
  display.print("Humidity: ");
  display.print(incomingData.humidity);
  display.println(" %");

  display.display();
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);

  esp_now_init();

  esp_now_register_recv_cb(OnDataRecv);

  Wire.begin();
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
}

void loop() {}

Practical Applications

Using ESP-NOW with OLED display opens many possibilities:

1. Wireless Weather Station

• ESP32 with BME280 sends climate data
• OLED receiver shows values

2. Wireless Button Control

You have already built an article on:

Wireless Button Control Using ESP-NOW

Similarly, OLED can show:

• Button ON/OFF
• Device triggered

3. Industrial Monitoring Panel

• ADC voltage readings
• Motor status
• Alert messages

4. Home Automation Dashboard

• Smart switch feedback
• Door sensor status
• Light intensity

Advantages Over Cloud-Based Display

• No internet required
• More privacy
• Faster response
• Lower cost
• Works during Wi-Fi outage

Limitations

• Range limited to ~100m
• Requires MAC pairing
• Small packet size (250 bytes)

Tips for Better OLED Interface

• Use larger fonts for critical data
• Add icons
• Implement scrolling text
• Show RSSI signal strength
• Display last update time

Troubleshooting Guide

OLED Not Displaying Data

• Check I2C address (0x3C or 0x3D)
• Verify wiring
• Ensure receiver in STA mode

ESP-NOW Communication Fail

• Correct MAC address
• Use same channel
• Reduce structure size

Best Practices

• Always use structured packets
• Add checksum if needed
• Use encryption for sensitive data
• Implement watchdog timers
• Refresh OLED efficiently

Conclusion

ESP-NOW with OLED Display is an excellent solution for offline IoT projects requiring wireless data visualization. It simplifies real-time monitoring without complex networking or cloud dependencies.

For your multi-device experiments and WSN setups, an OLED-based ESP-NOW receiver can act as a portable debug terminal and monitoring screen.