I’ve put together a flashing circuit and sketch (it’s seemed to have worked). The purpose of which is to read the ambient temperature and send it on to a MQTT server within my local network via WiFi. The temperature reading my MQTT server receives is over by about 23 C. The circuit reads about 33 C, and my house is about 17 C at most. I appreciate the DHT11 is only accurate to +/- 2 C but this reading is well over specification.
I’m using a DHT11 sensor module, coupled to an ESP-01S micro-controller. The sketch is something I’ve written myself to publish MQTT messages to a server. The connection to the Wifi network and Publishing of messages works as I’d expect. Power is a from a cheap variable bench PSU reading about 5.14V.
The source code for my sketch is as follows
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>
#define DELAY_TIME 10000
#define DELAY_TIME_SHORT 500
// Wifi Config
const char* ssid = "********";
const char* password = "********";
// MQTT Server config
const char* mqttServer = "********";
const int mqttPort = ****;
const char* mqttUser = "********";
const char* mqttPassword = "********";
// DHT config.
#define DHTTYPE DHT11
#define DHTPIN 2
// DHT Setup
DHT dht(DHTPIN, DHTTYPE);
float humidity, temp; // Values read from sensor
String bufString = ""; // String to display
char buf[128]; // Char array for MQTT
// Classes for Comms
WiFiClient espClient;
PubSubClient client(espClient);
void setup()
{
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED)
{
delay(DELAY_TIME_SHORT);
}
client.setServer(mqttServer, mqttPort);
// Connect to MQTT server
while (!client.connected()) {
if (client.connect("ESP8266Client", mqttUser, mqttPassword )) {
client.publish("esp/temp", "Init ESP8266");
}
}
delay(DELAY_TIME_SHORT);
// Initialize DHT11 device.
dht.begin();
}
void loop()
{
delay(DELAY_TIME);
humidity = dht.readHumidity(); // Read humidity (percent)
temp = dht.readTemperature(false); // Read temperature as Celcius
bufString = "Temp: " + String((int)temp) + " C, Humidity: " + String((int)humidity) + "%";
bufString.toCharArray(buf, 128);
client.publish("esp/temp", buf);
}
or can be seen here - https://pastebin.com/9YmXsEsb
Images of the Sensor/Module, my writing environment, and the MQTT messages can be seen here - ESP-01S with DHT11 Temperature reading inaccurate by +23 Deg C - Album on Imgur
Expected readings would have been around 17 C - 20 C. Using Arduino 1.8.9 on Arch Linux, DHT sensor library (by Adafruit) is at 1.3.0
I’m quite inexperienced with Arduino, MQTT, and these kind of projects (although I did a bit of Digital Electronics nearly 20 years ago) so forgive me if I’ve missed the obvious.
Thanks for your help
