In this particular example we are going to store temperature readings from a DHT11 on an sd card we will be using a Wemos mini and a variety of shields which make it easy to create projects like this with no wiring.
Lets take a look a the shields and boards that are required
| Image | Summary |
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The Wemos mini – ESP8266 based board, it comes with various headers. This is the beauty of it you can create stackable projects with the board and pin compatible shields |
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This shield features the DHT sensor, there are actually a couple of variations of this sensor which use slightly different sensors. The original was a dht11 and the newer one is a DHT12 |
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This allows you to use micro sd cards in your projects, The shield uses the SPI bus pins |
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This is simply a base, you plug the Wemos Mini into one side and you can plug a shield or shields into the other side |
Parts List
1 x Wemos Mini
1 x Wemos Dual Base
1 x Micro SD shield
1 x DHT shield (DHt11)
I connect the Wemos Mini to the dual base and then put the SD card shield along side this, I then place the DHT shield on top of the Wemos Mini.
Code
Various libraries required – you can install these via the library manager, here are links to them
https://github.com/adafruit/DHT-sensor-library
https://github.com/adafruit/Adafruit_Sensor
[codesyntax lang=”cpp”]
#include <SPI.h>
#include <SD.h>
#include “DHT.h”
#define DHTPIN D4 // what pin we’re connected to
#define DHTTYPE DHT11 // DHT 11
const int chipSelect = D8;
File myFile;
DHT dht(DHTPIN, DHTTYPE);
void setup()
{
// Open serial communications and wait for port to open:
Serial.begin(9600);
//init SD card
Serial.print(“Initializing SD card…”);
if (!SD.begin(chipSelect))
{
Serial.println(“initialization failed!”);
return;
}
Serial.println(“initialization done.”);
}
void loop()
{
myFile = SD.open(“tempdata.csv”, FILE_WRITE);//change the file name if you want
delay(2000);
float h = dht.readHumidity();
float t = dht.readTemperature();
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(“Failed to read from DHT sensor!”);
return;
}
//debug
Serial.print(“Humidity: “);
Serial.print(h);
Serial.print(” %\t”);
Serial.print(“Temperature: “);
Serial.print(t);
Serial.print(” *C “);
Serial.print(f);
Serial.print(” *F\t”);
// if the file opened okay, write to it:
if (myFile)
{
Serial.print(“Writing to tempdata.csv…”);
myFile.print(h);
myFile.print(“,”);
myFile.print(t);
myFile.print(“,”);
myFile.println(f);
// close the file:
myFile.close();
Serial.println(“done.”);
}
else
{
// if the file didn’t open, print an error:
Serial.println(“error opening tempdata.csv”);
}
}
[/codesyntax]
Again if you don’t want to type all of this in then you can download at wemos_sdcard_dht11
Output
Here is the output from the serial monitor and there will also be data on the sd card
Initializing SD card…initialization done.
Humidity: 19.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 20.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 20.00 % Temperature: 20.00 *C 68.00 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 21.00 *C 69.80 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 23.00 *C 73.40 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 23.00 *C 73.40 *F Writing to tempdata.csv…done.
Humidity: 19.00 % Temperature: 23.00 *C 73.40 *F Writing to tempdata.csv…done.
Links
Smart Electronics D1 mini – Mini NodeMcu 4M bytes development board based ESP8266 by WeMos
Dual Base Expansion board for WeMos D1 mini NodeMCU ESP8266
DHT Shield for WeMos D1 mini DHT11 Single-bus digital temperature and humidity sensor module sensor
Micro SD Card Shield IoT Wireless Control for D1 Mini ESP8266 WiFi WeMos Module