SainSmart 1.8 LCD / DHT-22 Temp / Humidity

I now have a DHT-22 Temperature and humidity module matched up with the SainSmart 1.8 TFT LCD. The tricky part of this project was converting floats to strings for the display. If you don’t need decimal point precision, you may not need this function, but it’s in there.

The DHT-22 connections and the SainSmart LCD connections are in the code.

Arduino TFT text example

This example demonstrates how to draw text on the
TFT with an Arduino. The Arduino reads the value
of an analog sensor attached to pin A0, and writes
the value to the LCD screen, updating every
quarter second.

This example code is in the public domain

Created 15 April 2013 by Scott Fitzgerald

Heavily modified to work with the DHT-22 code
by Steve Spence of


#include “TFT.h” // Arduino LCD library
#include “SPI.h” // Arduino SPI Library

// pin definition for the Uno
// SCL -> 13
// SDA -> 11
#define cs   10
#define dc   9
#define rst  8

// create an instance of the library
TFT TFTscreen = TFT(cs, dc, rst);

// char array to print to the screen
char tempPrintout[6];
char humPrintout[6];

// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain
// Fahrenheit conversion added by Steve Spence,

#include “DHT.h” //get the DHT library from

#define DHTPIN 2     // what pin we’re connected to

// Uncomment whatever type you’re using!
//#define DHTTYPE DHT11   // DHT 11
#define DHTTYPE DHT22   // DHT 22  (AM2302)
//#define DHTTYPE DHT21   // DHT 21 (AM2301)

// Connect pin + (middle) of the sensor to +5V
// Connect pin S  (on the right) of the sensor to whatever your DHTPIN is (2)
// Connect pin – (on the left) of the sensor to GROUND
// Connect 10k resistor between S and +

int cycleTime = 2000;


float h;
float t;

void setup() {

// Put this line at the beginning of every sketch that uses the GLCD:

// clear the screen with a black background
TFTscreen.background(0, 0, 0);

// write the static text to the screen
// set the font color to white
// set the font size
// write the text to the top left corner of the screen
TFTscreen.text(“Temp (F)”,0,0);
// write the text to the top left corner of the screen
TFTscreen.text(“Humidity (%)”,0,60);
// ste the font size very large for the loop



void loop() {

// Read the value of the temp/humidity sensor on D2

// Reading temperature or humidity takes about 250 milliseconds!
// Sensor readings may also be up to 2 seconds ‘old’ (its a very slow sensor)
h = dht.readHumidity();
t = dht.readTemperature();
t = (t*1.8)+32; //C to F conversion

String tempVal = doubleToString(t, 0); // decimal places of precision
String humVal = doubleToString(h, 0); // decimal places of precision
// String sensorVal = String(1.234);

// convert the reading to a char array
tempVal.toCharArray(tempPrintout, 6);
humVal.toCharArray(humPrintout, 6);

// set the font color
// print the sensor value
TFTscreen.text(tempPrintout, 0, 25);
TFTscreen.text(humPrintout, 0, 85);
// wait for a moment
// erase the text you just wrote
TFTscreen.text(tempPrintout, 0, 25);
TFTscreen.text(humPrintout, 0, 85);

//Rounds down (via intermediary integer conversion truncation)
String doubleToString(double input,int decimalPlaces){
String string = String((int)(input*pow(10,decimalPlaces)));
if(abs(input)<1 p=””>if(input>0)
string = “0”+string;
else if(input<0 p=””>string = string.substring(0,1)+”0″+string.substring(1);
return string.substring(0,string.length()-decimalPlaces)+”.”+string.substring(string.length()-decimalPlaces);
else {
return String((int)input);

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: