Data Logging - Espressif Systems ESP8266 Beginner's Manual

Data logging
A common use for IoT devices like the ESP8266 is monitoring sensors. Using the code in the previous example, we can request the
time, and save some sensor values to a file. If we run a server as well, we can show this data in a pretty graph in a webpage.
Temperature logger
In the following example, we'll use a DS18S20 temperature sensor to log the temperature over time and save it to the SPIFFS. It can
then be displayed in a graph in the browser.
Installing libraries
First, download the Dallas Temperature library by Miles Burton and the OneWire library by Jim Studt: Go to Sketch > Include Library ...
> Manage Libraries and search for 'Dallas Temperature' and 'OneWire' (make sure you download the correct version).
Hardware
Connect the ground of the DS18S20 temperature sensor (pin 1) to the ground of the ESP, connect the data pin (pin 2) to GPIO5, and
V (pin 3) to the 3.3V of the ESP. Finally, connect a 4k7Ω resistor between the data pin and V
CC
Libraries, constants and globals
#include <OneWire.h>
#include <DallasTemperature.h>
#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>
#include <WiFiUdp.h>
#include <ArduinoOTA.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>
#include <FS.h>
#define ONE_HOUR 3600000UL
#define TEMP_SENSOR_PIN 5
OneWire oneWire(TEMP_SENSOR_PIN); // Set up a OneWire instance to communicate with OneWire devices
DallasTemperature tempSensors(&oneWire); // Create an instance of the temperature sensor class
ESP8266WebServer server = ESP8266WebServer(80); // create a web server on port 80
File fsUploadFile; // a File variable to temporarily store the received file
ESP8266WiFiMulti wifiMulti; // Create an instance of the ESP8266WiFiMulti class, called 'wifiMulti'
const char *OTAName = "ESP8266"; // A name and a password for the OTA service
const char *OTAPassword = "esp8266";
const char* mdnsName = "esp8266"; // Domain name for the mDNS responder
WiFiUDP UDP; // Create an instance of the WiFiUDP class to send and receive UDP messages
IPAddress timeServerIP; // The time.nist.gov NTP server's IP address
const char* ntpServerName = "time.nist.gov";
const int NTP_PACKET_SIZE = 48; // NTP time stamp is in the first 48 bytes of the message
byte packetBuffer[ NTP_PACKET_SIZE]; // A buffer to hold incoming and outgoing packets
The only new things here are the OneWire and DallasTemperature libraries, to get the temperature from the sensor.
Setup
void setup() {
Serial.begin(115200); // Start the Serial communication to send messages to the computer
delay(10);
Serial.println("\r\n");
tempSensors.setWaitForConversion(false); // Don't block the program while the temperature sensor is reading
tempSensors.begin(); // Start the temperature sensor
if (tempSensors.getDeviceCount() == 0) {
Serial.printf("No DS18x20 temperature sensor found on pin %d. Rebooting.\r\n", TEMP_SENSOR_PIN);
Serial.flush();
ESP.reset();
}
startWiFi(); // Start a Wi-Fi access point, and try to connect to some given access points. Then wait for either an
AP or STA connection
startOTA(); // Start the OTA service
startSPIFFS(); // Start the SPIFFS and list all contents
startMDNS(); // Start the mDNS responder
startServer(); // Start a HTTP server with a file read handler and an upload handler
startUDP(); // Start listening for UDP messages to port 123
WiFi.hostByName(ntpServerName, timeServerIP); // Get the IP address of the NTP server
Serial.print("Time server IP:\t");
Serial.println(timeServerIP);
sendNTPpacket(timeServerIP);
}
CC.