Coder Legion - Recent posts tagged sensor

How to send sensor data to a gateway using PainlessMesh in ESP8266?

Mon, 20 Apr 2026 00:03:24 +0000

Hello, I'm Ganesh. I'm building git-lrc, an AI code reviewer that runs on every commit. It is free, unlimited, and source-available on Github. Star Us to help devs discover the project. Do give it a try and share your feedback for improving the product.

In this article, I will be demonstrating how to use PainlessMesh with a NodeMCUv2 (ESP8266) board and send data from one ESP8266 board to another ESP8266 board.

What Problem we are solving?

Previously we explored how to use MQTT with ESP8266.

Now let's integrate painlessmesh with MQTT.

Let's assume we have 2 ESP8266 boards.
One is gateway and another is node.

We want to send data from node to gateway using painlessmesh. Next we want to send data from gateway to cloud using MQTT.

For example we will use DHT11 sensor and mq series gas sensor with node to send data to gateway.

This operation should be done with very minimal data transfer.

If one node has 2 or more sensors it should be compressed and sent to gateway.

What We will be achieving?

Painlessmesh is very heavy library. It does lot of operations to keep network alive. With this if we send data without compressing it. It will consume lot of power and data. Casuing network to be unstable.

Main Goal is

Receive data from multiple sensors
Compress the data
Send the data to gateway
Publish the data from received at gateway to cloud using MQTT
Scallable MQTT topics publishing

I will be combining all the above mentioned in single project.

In this article we will be covering first 2 points.

Receiving Data from Multiple Sensors
Compressing the data
Send the data to gateway

Receiving Data from Multiple Sensors and Compressing it

For this example we will use DHT11 sensor and MQ2 gas sensor.

Setup connection with painlessmesh We will use these credentials for painlessmesh.

#define MESH_PREFIX "secreat_name"
#define MESH_PASSWORD "SecreateKey"
#define MESH_PORT 5555

With this funtion we create scheduler and painlessmesh object.

#include <painlessMesh.h>

  mesh.init(MESH_PREFIX, MESH_PASSWORD, &scheduler, MESH_PORT);
  mesh.onReceive(&onReceive);
  mesh.onNewConnection(&onNewConnection);

Setup connection with DHT11 sensor

We use DHT library sensor to measure temperature and humidity.

We use D2 pin to connect DHT11 sensor.

#include <DHT.h>
#define DHT_PIN D2
#define DHT_TYPE DHT11

DHT dht(DHT_PIN, DHT_TYPE);

Read the temperature and humidity from the sensor.

float t = dht.readTemperature();
float h = dht.readHumidity();

As Dht sensor should have 1 second delay between readings. We will use scheduler to read the temperature and humidity from the sensor.

Task readDHTTask(10000, TASK_FOREVER, []() {
    float t = dht.readTemperature();
    float h = dht.readHumidity();
    if (isnan(t) || isnan(h)) {
        Serial.println("Failed to read from DHT sensor!");
        return;
    }
    Serial.printf("Temperature: %.2f C, Humidity: %.2f %%", t, h);
});

Setup connection with MQ2 gas sensor

We use MQ2 gas sensor to measure the gas concentration.

We use A0 pin to connect MQ2 gas sensor.

#define MQ2_PIN A0

Read the gas concentration from the sensor.

float gas = analogRead(MQ2_PIN);

As MQ2 sensor should have 1 second delay between readings. We will use scheduler to read the gas concentration from the sensor.

Task readMQ2Task(10000, TASK_FOREVER, []() {
    float gas = analogRead(MQ2_PIN);
    if (isnan(gas)) {
        Serial.println("Failed to read from MQ2 sensor!");
        return;
    }
    Serial.printf("Gas: %.2f ppm", gas);
});

Compress the data with bit packing

We use bit packing to compress the data.

As sensor will be in specified range we can use bit packing to compress the data.

String packToHex(float temp, float hum, float gas) {
  uint16_t packedTemp = (uint16_t)(temp * 10.0f) & 0x1FF;         // 9 bits
  uint16_t packedHum = (uint16_t)((hum - 20.0f) * 10.0f) & 0x3FF; // 10 bits
  uint16_t packedGas = (uint16_t)(gas / 10.0f) & 0x3FF;           // 10 bits

  uint32_t packed = 0;
  packed |= (uint32_t)packedTemp << 20; // bits 28-20
  packed |= (uint32_t)packedHum << 10;  // bits 19-10
  packed |= (uint32_t)packedGas;        // bits  9-0

  char buf[9];
  snprintf(buf, sizeof(buf), "%08X", packed);
  return String(buf);
}

Finaly commbining all these into one code.

/**
 * sensor_node_1.cpp — PainlessMesh Sensor Node (DHT11 + MQ6)
 *
 * Boot flow:
 *   1. Joins the mesh network
 *   2. On first connection to gateway → broadcasts /config (packing schema)
 *      The gateway forwards /config to MQTT → backend caches the schema
 *   3. After 3 s delay → starts sending /data every 5 s
 *      (gives backend time to process /config before first hex payload arrives)
 *
 * /alert is sent immediately any time gas > GAS_THRESHOLD.
 *
 * Bit packing layout (29 bits used, 3 MSBs unused):
 *   bits 28-20 (9 bits) : temp  = temp_celsius * 10        (0–511 → 0–51.1°C)
 *   bits 19-10 (10 bits): hum   = (humidity - 20) * 10     (0–1023 → 20–122.3%)
 *   bits  9-0  (10 bits): gas   = gas_ppm / 10             (0–1023 → 0–10230
 * ppm)
 */

#include <Arduino.h>
#include <ArduinoJson.h>
#include <DHT.h>
#include <painlessMesh.h>

// ─── Mesh credentials (must match gateway) ───────────────────────────────────
#define MESH_PREFIX "secreat_name"
#define MESH_PASSWORD "SecreateKey"
#define MESH_PORT 5555

// ─── Sensor pins ─────────────────────────────────────────────────────────────
#define DHT_PIN D2
#define DHT_TYPE DHT11
#define MQ6_PIN A0 // analog pin

// ─── Alert threshold ─────────────────────────────────────────────────────────
#define GAS_THRESHOLD 5000 // ppm — triggers /alert

// ─── Timing ──────────────────────────────────────────────────────────────────
#define DATA_INTERVAL_MS 5000

// ─── Globals ─────────────────────────────────────────────────────────────────
Scheduler scheduler;
painlessMesh mesh;
DHT dht(DHT_PIN, DHT_TYPE);
bool configSent = false; // send /config once per gateway connection

// ─── Bit packing ─────────────────────────────────────────────────────────────

/**
 * Pack temperature, humidity and gas into an 8-char hex string.
 * The encoding matches what the backend's unpackHex() expects.
 *
 *   temp  → 9 bits, mult 10, min 0
 *   hum   → 10 bits, mult 10, min 20
 *   gas   → 10 bits, div 10, min 0
 */
String packToHex(float temp, float hum, float gas) {
  uint16_t packedTemp = (uint16_t)(temp * 10.0f) & 0x1FF;         // 9 bits
  uint16_t packedHum = (uint16_t)((hum - 20.0f) * 10.0f) & 0x3FF; // 10 bits
  uint16_t packedGas = (uint16_t)(gas / 10.0f) & 0x3FF;           // 10 bits

  uint32_t packed = 0;
  packed |= (uint32_t)packedTemp << 20; // bits 28-20
  packed |= (uint32_t)packedHum << 10;  // bits 19-10
  packed |= (uint32_t)packedGas;        // bits  9-0

  char buf[9];
  snprintf(buf, sizeof(buf), "%08X", packed);
  return String(buf</spa

How to Connect a DHT11 to a NodeMCU v2 board?

Tue, 14 Apr 2026 20:49:32 +0000

In this article, we will see how to work with DHT11 sensor with NodeMCU v2 using PlatformIO.

Hardware Check

We should always check datasheets before working with any hardware.

So, by checking the datasheet of DHT11 and NodeMCU v2, we can determine how connection should be done and how to create firmware for it.

You can check datasheets here:

Power Compatibility

As per the datasheet of DHT11, it can operate on a supply range of 3V to 5.5V DC.
Since the NodeMCU v2 runs on 3.3V.

You can power the sensor directly from the NodeMCU's 3V3 pin. This keeps your build simple and safe without needing extra voltage regulators.

Also they recommend to use a pull-up resistor of 4.7K to 10K between VDD and DATA pins.To make sure data is read properly.

Hardware Identification

Check which version of the DHT11 you have. This changes how many pins you’ll be dealing with.

Feature	Bare DHT11 Sensor	DHT11 Module
Appearance	Blue plastic square with 4 metal pins.	Sensor soldered onto a small PCB.
Pin Count	4 Pins.	3 Pins.
Resistor	Required. You must add your own 4.7K to 10K resistor.	Built-in. Usually pre-soldered on the board.

Step-by-Step Wiring Guide

For the 4-Pin Bare Sensor

If you are using the bare sensor, follow this pinout based on the official datasheet:

Pin 1 (VDD): Connect to the 3V3 pin on the NodeMCU.
Pin 2 (DATA): Connect to a digital pin like D1 or D2.
- Crucial Step: Place a 4.7K to 10K pull-up resistor between Pin 1 (VDD) and Pin 2 (DATA). This prevents the signal from "floating" and ensures stable data readings.
Pin 3 (NULL): Leave this disconnected. It serves no electrical purpose.
Pin 4 (GND): Connect to any GND pin on the NodeMCU.

For the 3-Pin Module

If you have the module, life is even easier. The board is usually labeled:

VCC (+): Connect to 3V3.
DATA (out): Connect to D1 or D2.
GND (-): Connect to GND.

Why the Pull-up Resistor Matters?

Without a pull-up resistor, the DATA line doesn't have a clear "High" or "Low" state when the sensor isn't talking, which leads to erratic readings or "Sensor not found" errors.

If you're using the bare sensor, don't skip the 4.7K to 10K resistor (though anything from 4.7K to 10K usually works in a pinch!).

Coding Your DHT11 with PlatformIO

Now that the hardware is ready.

Since we are using PlatformIO, we’ll need to configure our project environment and use the industry-standard Adafruit library.

1. Configure `platformio.ini`

First, we need to tell PlatformIO which board we are using and which library to download. Open your platformio.ini file and ensure it looks like this:

[env:nodemcuv2]
platform = espressif8266
board = nodemcuv2
framework = arduino
monitor_speed = 115200
lib_deps = 
    adafruit/DHT sensor library @ ^1.4.6
    adafruit/Adafruit Unified Sensor @ ^1.1.14

Note: The Adafruit Unified Sensor library is a hidden dependency that the DHT library needs to function correctly.

2. The Main Code (`src/main.cpp`)

In your project’s src folder, open main.cpp. We’ll use a modified version of your snippet specifically tuned for the DHT11.

#include <Arduino.h>
#include "DHT.h"

// Define the NodeMCU pin connected to the DHT11 data pin
// Using D2 (GPIO 4) as per our wiring guide
#define DHTPIN D2     

// Since we are using the DHT11, we specify it here
#define DHTTYPE DHT11   

// Initialize the DHT sensor
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  // Start serial communication at the speed defined in platformio.ini
  Serial.begin(115200);
  Serial.println(F("DHT11 Sensor Initializing..."));

  // Start the sensor
  dht.begin();
}

void loop() {
  // Wait 2 seconds between measurements. 
  // DHT11 is slower than modern sensors; don't rush it!
  delay(2000);

  // Reading temperature or humidity takes about 250 milliseconds!
  float h = dht.readHumidity();
  float t = dht.readTemperature(); // Celsius
  float f = dht.readTemperature(true); // Fahrenheit

  // Check if any reads failed
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Failed to read from DHT sensor! Check your wiring."));
    return;
  }

  // Compute heat index (how it actually feels)
  float hic = dht.computeHeatIndex(t, h, false);

  // Print results to the Serial Monitor
  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  |  Temp: "));
  Serial.print(t);
  Serial.print(F("°C  |  Heat Index: "));
  Serial.print(hic);
  Serial.println(F("°C"));
}

DHT11 Sensor Initializing...
Humidity: 45.00 %  |  Temp: 25.00°C  |  Heat Index: 25.00°C
Humidity: 46.00 %  |  Temp: 25.12°C  |  Heat Index: 25.12°C
Humidity: 45.00 %  |  Temp: 25.25°C  |  Heat Index: 25.25°C

Key Adjustments for the DHT11

DHTTYPE: Ensure this is set to DHT11. While the code for a DHT22 is almost identical, the timing and data conversion logic inside the library are different for these two models.
Sampling Rate: The DHT11 has a sampling rate of about 1Hz (one reading per second). Using a delay(2000) (2 seconds) is a "safe bet" to ensure you don't get stale data or errors.
Accuracy Note: Don't be surprised if the readings are slightly different from your home thermostat. The DHT11 is an entry-level sensor with an accuracy of ±2°C for temperature and ±5% for humidity.

Conclusion

We could able to connect DHT11 sensor with NodeMCU v2 using PlatformIO and read temperature and humidity values.

In next article we will learn different sensor.

Any feedback or contributors are welcome! It’s online, source-available, and ready for anyone to use.
⭐ Star it on GitHub: https://github.com/HexmosTech/git-lrc

How to use the DHT22 sensor with ESP8266?

Fri, 03 Apr 2026 10:24:39 +0000

In this article, I will be explaining how to use DHT22 sensor with ESP8266.

Setup Requirements

Most of use confuse with DHT11 and DHT22.

Both are temperature and humidity sensors. But they have different specifications.

DHT22 is more accurate than DHT11.

For visual identification, DT22 comes in white color while DHT11 comes in blue color.

Once this is correctly identified, and have a datasheet with us. We can proceed with the setup.

Integrate Using Pre-built Libraries.

Most of the sensor manufacturers provide libraries for their sensors. Also if they don't provide libraries, we can find libraries for them in the internet.

Mostly we can use arduino IDE for searching libraries.

we can use platformio by just adding the library name in the lib_deps section of platformio.ini file.

PlatformIO Setup

Go to PlatformIO extension in VSCode.

Click on Create New Project.

Give Project Name.
Select the board in my case it was NodeMCU 1.0 (ESP-12E Module).
Select Framework as Arduino.

You can see platformio.ini file with the following content:

; PlatformIO Project Configuration File
;
;   Build options: build flags, source filter
;   Upload options: custom upload port, speed and extra flags
;   Library options: dependencies, extra library storages
;   Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html
; Common settings for both environments
; Common settings for both environments
[env]
platform = espressif8266
board = nodemcuv2
framework = arduino
monitor_speed = 115200

How to Code for DHT22 Sensor with ESP8266?

Now we setup project

Let's add library for DHT sensor.

lib_deps = 
    adafruit/DHT sensor library@^1.4.4

In the main code let's add the following code.

#include "DHT.h"

// Define the NodeMCU pin connected to the DHT22 data pin
#define DHTPIN D2     

// Define the sensor type
// If yours is DHT11, then change it to DHT11

#define DHTTYPE DHT22   

// Initialize the DHT sensor
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  // Start the serial communication
  Serial.begin(115200);
  Serial.println(F("DHT22 Sensor Test with NodeMCU!"));

  // Start the sensor
  dht.begin();
}

void loop() {
  // Wait a few seconds between measurements.
  // The DHT22 requires about 2 seconds to stabilize between readings.
  delay(2000);

  // Read humidity
  float h = dht.readHumidity();
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit (isFahrenheit = true)
  float f = dht.readTemperature(true);

  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Failed to read from DHT sensor!"));
    return;
  }

  // Compute heat index in Fahrenheit (the default)
  float hif = dht.computeHeatIndex(f, h);
  // Compute heat index in Celsius (isFahreheit = false)
  float hic = dht.computeHeatIndex(t, h, false);

  // Print the results to the Serial Monitor
  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  Temperature: "));
  Serial.print(t);
  Serial.print(F("°C "));
  Serial.print(f);
  Serial.print(F("°F  Heat index: "));
  Serial.print(hic);
  Serial.print(F("°C "));
  Serial.print(hif);
  Serial.println(F("°F"));
}

In here we are setting up the DHT22 sensor with ESP8266.

Initialize DHT sensor.

Start DHT sensor.

Read humidity.

Read temperature.

Read heat index.

Print the results.

Compile and Connection of DHT22 with ESP8266

Now we can see tick mark in the bottom of the VSCode.

On clicking it we can verify the code is compiling.

Output 1:

Checking size .pio/build/sensor_node_1/firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [===       ]  34.5% (used 28236 bytes from 81920 bytes)
Flash: [===       ]  26.3% (used 274819 bytes from 1044464 bytes)
======================================================================= [SUCCESS] Took 0.56 seconds =======================================================================

After compilation we can upload the code to the ESP8266 by clicking the upload button.

Now we can connect the vin pin of DHT22 to 3V3 pin of ESP8266 and gnd pin of DHT22 to gnd pin of ESP8266.
Data pin of DHT22 to D2 pin of ESP8266.

Uploading the code to ESP8266

Connect ESP8266 to the computer and click on arrow button.

Output 2:

Writing at 0x0002c000... (92 %)
Writing at 0x00030000... (100 %)
Wrote 278976 bytes (204732 compressed) at 0x00000000 in 18.0 seconds (effective 123.7 kbit/s)...
Hash of data verified.

Leaving...
Hard resetting via RTS pin...

Finally we can see the output in the serial monitor on clicking socket button.

Output 3:

DHT22 Sensor Test with NodeMCU!
Humidity: 51.80%  Temperature: 31.30°C 88.34°F  Heat index: 33.51°C 92.31°F
Humidity: 51.80%  Temperature: 31.30°C 88.34°F  Heat index: 33.51°C 92.31°F
Humidity: 51.80%  Temperature: 31.30°C 88.34°F  Heat index: 33.51°C 92.31°F
Humidity: 51.70%  Temperature: 31.30°C 88.34°F  Heat index: 33.49°C 92.27°F

Conclusion

Now we could able to setup and test DHT22 sensor with ESP8266.

Any feedback or contributors are welcome! It’s online, source-available, and ready for anyone to use.
⭐ Star it on GitHub: https://github.com/HexmosTech/git-lrc

Coder Legion - Recent posts tagged sensor

How to send sensor data to a gateway using PainlessMesh in ESP8266?

What Problem we are solving?

What We will be achieving?

Receiving Data from Multiple Sensors and Compressing it

How to Connect a DHT11 to a NodeMCU v2 board?

Hardware Check

Power Compatibility

Hardware Identification

Step-by-Step Wiring Guide

For the 4-Pin Bare Sensor

For the 3-Pin Module

Why the Pull-up Resistor Matters?

Coding Your DHT11 with PlatformIO

1. Configure platformio.ini

2. The Main Code (src/main.cpp)

Key Adjustments for the DHT11

Conclusion

How to use the DHT22 sensor with ESP8266?

Setup Requirements

Integrate Using Pre-built Libraries.

PlatformIO Setup

How to Code for DHT22 Sensor with ESP8266?

Compile and Connection of DHT22 with ESP8266

Uploading the code to ESP8266

Conclusion

1. Configure `platformio.ini`

2. The Main Code (`src/main.cpp`)