Published July 30, 2025 © GPL3+

Digital Lab Sensor Display

Display climate data across rooms — no Wi-Fi needed!

BeginnerFull instructions provided6 hours97

Things used in this project

Hardware components

Seeed Studio XIAO ESP32S3 Sense

Seeed Studio XIAO ESP32C3

Maxim Integrated MAXREFDES99# MAX7219 Display Driver Shield

Seeed Studio Grove - Temperature&Humidity Sensor (SHT40)

Jumper wires (generic)

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

Soldering iron (generic)

Solder Wire, Lead Free

Story

Modern digital labs require not just computing power, but also real-time awareness of the environment. In this project, you'll build a wireless temperature and humidity display system using two ESP32 boards, a SHT40 sensor, and a MAX7219 LED matrix.

But here’s the twist — it doesn’t need Wi-Fi or an internet connection.

We use ESP-NOW, a fast, connectionless communication protocol built into the ESP32, to send live sensor data from one device to another. That makes it perfect for use in a classroom, university digital lab, or any isolated IoT setup where reliability and simplicity are key.

The receiver unit displays the environmental data on a large LED matrix, alternating between temperature, humidity, and a scrolling label like “DIGITAL LAB MONITOR.”

This system helps visualize your lab's real-time climate conditions in a clean, readable, and fully offline manner.

Whether you're teaching embedded systems, building a smart environment, or upgrading your digital lab infrastructure, this project blends sensor integration, wireless communication, and visual feedback in a powerful way.

How It Works

Sender ESP32 reads temperature and humidity from the SHT40 sensor.
It then sends that data using ESP-NOW, a fast and connectionless protocol for ESP32 devices.
Receiver ESP32 gets the data and shows it on a scrolling MAX7219 matrix display, alternating between temperature, humidity, and a custom message.

No Wi-Fi, no MQTT, just fast peer-to-peer wireless communication.

Display Modes

The LED matrix cycles through:

Current Temperature (e.g. 26.4C)
Current Humidity (e.g. 61.2%)
Custom scrolling message: DIGITAL LAB MONITOR

Each display stays for 12 seconds before switching.

Circuit Diagrams

Sender Node (Xiao ESP32S3 + SHT40)

SHT40 uses I2C (SDA/SCL)

Connect as per your board’s pinout (usually GPIO 21/22)

Receiver Node (Xiao ESP32C3 + MAX7219)

MAX7219 uses SPI (DIN, CS, CLK)

DIN → GPIO 10
CS → GPIO 5
CLK → GPIO 8

Getting Started

Upload sender code to one ESP32 and connect the SHT40
Upload receiver code to another ESP32 and wire up the MAX7219
Power both boards
Watch the temperature and humidity scroll across the display!

Make sure to update the MAC address of the receiver in the sender sketch!

use this code to get the mac address for the receiver side

#include <WiFi.h>
#include <esp_wifi.h>

void readMacAddress(){
  uint8_t baseMac[6];
  esp_err_t ret = esp_wifi_get_mac(WIFI_IF_STA, baseMac);
  if (ret == ESP_OK) {
    Serial.printf("%02x:%02x:%02x:%02x:%02x:%02x\n",
                  baseMac[0], baseMac[1], baseMac[2],
                  baseMac[3], baseMac[4], baseMac[5]);
  } else {
    Serial.println("Failed to read MAC address");
  }
}

void setup(){
  Serial.begin(115200);

  WiFi.mode(WIFI_STA);
  WiFi.STA.begin();

  Serial.print("[DEFAULT] ESP32 Board MAC Address: ");
  readMacAddress();
}
 
void loop(){

}

Possible Extensions

Add a buzzer to the receiver to alert high temperatures
Display data on an OLED instead of matrix
Add more sensors (e.g., CO₂, light, motion)
Send to multiple displays at once

Conclusion

This project is a great way to explore ESP-NOW, sensor data collection, and LED display output — all without relying on internet access. Whether for labs, classrooms, or fun DIY experiments, this setup makes wireless monitoring simple and eye-catching.

Schematics

Code

#include <esp_now.h>
#include <WiFi.h>
#include <Adafruit_SHT4x.h>

// Create SHT40 object
Adafruit_SHT4x sht4 = Adafruit_SHT4x();

// Structure to send
typedef struct struct_message {
  float temperature;
  float humidity;
} struct_message;

struct_message msg;

// Receiver MAC address (update this according to your esp32 mac address!)

uint8_t receiverAddress[] = {0xE4, 0xB3, 0x23, 0xC3, 0x6C, 0x28};
void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("Delivery Status: ");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Success" : "Fail");
}

void setup() {
  Serial.begin(115200);
  delay(500);

  // Initialize sensor
  if (!sht4.begin()) {
    Serial.println("Couldn't find SHT4x sensor!");
    while (1) delay(10);
  }
  sht4.setPrecision(SHT4X_HIGH_PRECISION);
  sht4.setHeater(SHT4X_NO_HEATER);

  // Initialize WiFi + ESP-NOW
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();

  if (esp_now_init() != ESP_OK) {
    Serial.println("ESP-NOW init failed");
    return;
  }

  esp_now_register_send_cb(OnDataSent);

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

  if (!esp_now_is_peer_exist(receiverAddress)) {
    if (esp_now_add_peer(&peerInfo) != ESP_OK) {
      Serial.println("Failed to add peer");
      return;
    }
  }

  Serial.println("ESP-NOW sender with SHT40 ready");
}

void loop() {
  sensors_event_t humidity, temperature;
  sht4.getEvent(&humidity, &temperature);
  
  msg.temperature = temperature.temperature;
  msg.humidity = humidity.relative_humidity;

  Serial.print("Sending temperature: ");
  Serial.print(msg.temperature);
  Serial.print(" °C, humidity: ");
  Serial.print(msg.humidity);
  Serial.println(" %");

  esp_err_t result = esp_now_send(receiverAddress, (uint8_t*)&msg, sizeof(msg));
  if (result == ESP_OK) {
    Serial.println("Message sent");
  } else {
    Serial.println("Send failed");
  }

  delay(5000); // Send every 5 seconds
}

#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <esp_now.h>
#include <WiFi.h>
#include <SPI.h>

// MAX7219 config
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
#define MAX_DEVICES 4
#define DATA_PIN  10
#define CLK_PIN   8
#define CS_PIN    5

MD_Parola display = MD_Parola(HARDWARE_TYPE, DATA_PIN, CLK_PIN, CS_PIN, MAX_DEVICES);

// Static scrolling text
const char* runningText = "DIGITAL LAB MONITOR";

// Display mode switching
unsigned long lastSwitch = 0;
int mode = 0; // 0: temperature, 1: humidity, 2: running text
const int switchInterval = 7000; // 12 seconds

// Latest received values
volatile float temperatureValue = 0.0;
volatile float humidityValue = 0.0;
unsigned long lastReceived = 0; // Time of last valid data
const unsigned long dataTimeout = 10000; // 10 seconds

// Structure for ESP-NOW message
typedef struct struct_message {
  float temperature;
  float humidity;
} struct_message;

// ESP-NOW receive callback
void OnDataRecv(const esp_now_recv_info_t *recvInfo, const uint8_t *data, int len) {
  if (len == sizeof(struct_message)) {
    struct_message receivedData;
    memcpy(&receivedData, data, sizeof(receivedData));

    temperatureValue = receivedData.temperature;
    humidityValue = receivedData.humidity;
    lastReceived = millis(); // Update timestamp

    // Print sender MAC and data
    char macStr[18];
    const uint8_t *mac = recvInfo->src_addr;
    snprintf(macStr, sizeof(macStr),
             "%02X:%02X:%02X:%02X:%02X:%02X",
             mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
    
    Serial.printf("Received from %s: Temp = %.2f °C, Humidity = %.2f %%\n", macStr, temperatureValue, humidityValue);
  }
}

void setup() {
  Serial.begin(115200);
  display.begin();
  display.setIntensity(8);
  display.displayClear();

  WiFi.mode(WIFI_STA);
  if (esp_now_init() != ESP_OK) {
    Serial.println("ESP-NOW init failed");
    return;
  }

  esp_now_register_recv_cb(OnDataRecv);

  display.displayScroll("ESP-NOW Receiver Ready", PA_LEFT, PA_SCROLL_LEFT, 50);
  while (!display.displayAnimate()) {
    // Wait until the startup message scrolls
  }
  display.displayClear();
}

void loop() {
  unsigned long nowMillis = millis();

  // Reset values if no data received recently
  if ((nowMillis - lastReceived) > dataTimeout) {
    temperatureValue = 0.0;
    humidityValue = 0.0;
  }

  // Toggle mode every switchInterval
  if (nowMillis - lastSwitch > switchInterval) {
    mode = (mode + 1) % 3;
    lastSwitch = nowMillis;
    display.displayClear();
  }

  if (mode == 0) {
    // Show temperature
    char buffer[10];
    snprintf(buffer, sizeof(buffer), "%.1fC", temperatureValue);
    display.setTextAlignment(PA_CENTER);
    display.print(buffer);
    delay(1000);
  } else if (mode == 1) {
    // Show humidity
    char buffer[10];
    snprintf(buffer, sizeof(buffer), "%.1f%%", humidityValue);
    display.setTextAlignment(PA_CENTER);
    display.print(buffer);
    delay(1000);
  } else {
    // Show scrolling text
    if (display.displayAnimate()) {
      display.displayScroll(runningText, PA_LEFT, PA_SCROLL_LEFT, 50);
    }
  }
}

Credits

Hendra Kusumah

47 projects • 159 followers

Love hacking and making new things from IoT to robotics

Digital Lab Sensor Display

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

How It Works

Display Modes

Circuit Diagrams

Sender Node (Xiao ESP32S3 + SHT40)

Receiver Node (Xiao ESP32C3 + MAX7219)

Getting Started

Possible Extensions

Conclusion

Custom parts and enclosures

schematic

Schematics

schematic

Code

sender code

receiver code

Credits

Hendra Kusumah

Comments

Embed the widget on your own site

Digital Lab Sensor Display

Digital Lab Sensor Display

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

How It Works

Display Modes

Circuit Diagrams

Sender Node (Xiao ESP32S3 + SHT40)

Receiver Node (Xiao ESP32C3 + MAX7219)

Getting Started

Possible Extensions

Conclusion

Custom parts and enclosures

schematic

Schematics

schematic

Code

sender code

receiver code

Credits

Hendra Kusumah

Comments

Related channels and tags