ESP8266 WiFi Sensor Network on a Breadboard

The ESP8266 is an 80–160 MHz Tensilica L106 SoC with a full 802.11 b/g/n WiFi stack built in. The ESP-01 module — the smallest form factor — costs about 9 RON per piece at Optimus Digital. Three of them, a Raspberry Pi acting as an MQTT broker, a handful of DHT11 sensors and some passive components add up to under 120 RON for a three-node indoor temperature and humidity mesh.

This article covers the hardware shopping list, programming the ESP-01 with Arduino IDE via a USB-UART adapter, writing a minimal MQTT publish sketch, setting up the Mosquitto broker on the Raspberry Pi, and subscribing to the data stream with a Python script.

The ESP-01 and its limitations

The ESP-01 breaks out only two GPIO pins (GPIO0 and GPIO2) alongside the UART lines (TX, RX), power (3.3 V) and ground. That is enough for a single-wire DHT sensor or a Dallas DS18B20 temperature probe, but not enough for multi-sensor arrays. For those, the ESP-12E module (used on the NodeMCU and Wemos D1 Mini boards) exposes 11 usable GPIOs and costs about 16 RON at Robofun — a better choice if you plan to expand later.

The ESP-01 draws up to 250 mA during WiFi transmission bursts. A USB power bank or a 3.3 V linear regulator powered from a 5 V source must handle this peak. The AMS1117-3.3 is the standard choice: it is stocked at Elecpro for 1.20 RON per piece and handles up to 800 mA continuous.

Shopping list (3-node build)

3 × ESP-01 module — 27 RON total at Optimus Digital
3 × DHT11 temperature and humidity sensor — 9 RON total at Robofun
3 × AMS1117-3.3 voltage regulator — 3.60 RON total at Elecpro
3 × 10 µF electrolytic capacitor (decoupling on the 3.3 V rail) — 2 RON total
3 × 100 nF ceramic capacitor — 1.20 RON total
1 × USB-to-UART adapter (CH340 or CP2102) — 12 RON at Optimus Digital, reusable across all nodes
1 × full-size breadboard — 15 RON at Robofun
Jumper wire kit — 8 RON at Optimus Digital
Raspberry Pi 3 B or 4 (if you already have one, cost is zero; otherwise budget 180 RON)

Total without the Pi: approximately 78 RON. With a Pi: approximately 258 RON.

Programming the ESP-01 with Arduino IDE

Install the ESP8266 board package in Arduino IDE by adding http://arduino.esp8266.com/stable/package_esp8266com_index.json to File → Preferences → Additional Boards Manager URLs. Open the Boards Manager, search for esp8266 and install version 3.x.

To upload firmware to the ESP-01, connect the USB-UART adapter as follows: RX on the adapter to TX on the ESP-01, TX on the adapter to RX on the ESP-01, GND to GND and 3.3 V to VCC. Pull GPIO0 low (connect to GND) before applying power to enter the bootloader. Select Generic ESP8266 Module as the board and set the upload speed to 115200 baud.

A minimal MQTT publish sketch

Install the PubSubClient library via the Arduino Library Manager (search for PubSubClient by Nick O'Leary).

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

const char* ssid      = "YOUR_SSID";
const char* password  = "YOUR_PASSWORD";
const char* mqttHost  = "192.168.1.200";
const int   mqttPort  = 1883;
const char* nodeId    = "node01";

DHT dht(2, DHT11);
WiFiClient wifiClient;
PubSubClient mqtt(wifiClient);

void connectWifi() {
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) delay(500);
}

void connectMqtt() {
  while (!mqtt.connected()) {
    mqtt.connect(nodeId);
    delay(500);
  }
}

void setup() {
  dht.begin();
  connectWifi();
  mqtt.setServer(mqttHost, mqttPort);
  connectMqtt();
}

void loop() {
  mqtt.loop();
  float temperature = dht.readTemperature();
  float humidity    = dht.readHumidity();
  if (!isnan(temperature)) {
    char payload[32];
    snprintf(payload, sizeof(payload), "%.1f", temperature);
    mqtt.publish("sensors/node01/temperature", payload);
    snprintf(payload, sizeof(payload), "%.1f", humidity);
    mqtt.publish("sensors/node01/humidity", payload);
  }
  delay(30000);
}

Replace nodeId with node02 and node03 for the other two ESP-01 modules, and update the topic strings accordingly. The 30-second interval keeps the WiFi radio active but reduces the duty cycle to about 5%, which matters for battery-powered nodes.

Setting up Mosquitto on the Raspberry Pi

On Raspberry Pi OS, install Mosquitto with:

sudo apt update && sudo apt install -y mosquitto mosquitto-clients

By default, Mosquitto 2.x requires explicit configuration to allow unauthenticated connections from the LAN. Create /etc/mosquitto/conf.d/local.conf with:

listener 1883
allow_anonymous true

Then restart the service:

sudo systemctl restart mosquitto

Verify that Node 1 is publishing by running on the Pi:

mosquitto_sub -h localhost -t "sensors/#" -v

You should see lines such as sensors/node01/temperature 22.5 every 30 seconds once the ESP-01 connects.

Subscribing and logging with Python

Install the paho-mqtt library on the Pi:

pip3 install paho-mqtt

A minimal logger that appends CSV rows to a file:

import paho.mqtt.client as mqtt
import csv, time, os

LOG_FILE = "/home/pi/sensors.csv"

def on_message(client, userdata, msg):
    with open(LOG_FILE, "a", newline="") as f:
        writer = csv.writer(f)
        writer.writerow([time.strftime("%Y-%m-%d %H:%M:%S"), msg.topic, msg.payload.decode()])

client = mqtt.Client()
client.on_message = on_message
client.connect("localhost", 1883)
client.subscribe("sensors/#")
client.loop_forever()

Run it with python3 logger.py & or configure it as a systemd service so it restarts automatically after reboots.

Range and interference notes

The ESP-01's PCB antenna is rated for about 40 m line-of-sight. In a typical Romanian apartment with concrete walls, expect 8–15 m through one or two walls before the RSSI drops below -80 dBm and connections become unstable. Placing nodes close to the access point or using a mesh router (such as those available in Altex's TP-Link Deco range) extends coverage without adding infrastructure complexity to the project.

ESP8266 WiFi Sensor Network on a Breadboard — Under 120 RON