DHT sensors with RGB LED

Question

I have a DHT11 that outputs temperature and humidity values to my serial monitor. I'm trying to serial the COLOUR of the light based on the temperature conditions. So far I only get 1's and 0's. How can I change these integer values to output string say RED, GREEN or BLUE?

Code

#include <dht.h>
dht DHT;
#define DHT11_PIN A5
int redPin = 10; // Red LED, connected to digital pin 10
int grnPin = 9; // Green LED, connected to digital pin 9
int bluPin = 8; // Blue LED, connected to digital pin 8
void setup() {
 Serial.begin(9600);
 // Sets the pins as output for RGB LED
 pinMode(redPin, OUTPUT);
 pinMode(grnPin, OUTPUT);
 pinMode(bluPin, OUTPUT);
}
void loop() {
 int chk = DHT.read11(DHT11_PIN);
 int t = DHT.temperature;
 int h = DHT.humidity;
 Serial.print("Temperature = ");
 Serial.print(t);
 Serial.print( "," );
 Serial.print("Humidity = ");
 Serial.print(h);
 Serial.print("\n");
 delay(60000);
 if((DHT.temperature < 26) && (DHT.temperature >= 23.2)) {
 // Writing the LED colour pins HIGH or LOW to set colours
 digitalWrite(redPin, HIGH); // yellow
 digitalWrite(grnPin, HIGH);
 delay(100);
 digitalWrite(bluPin, LOW);
 }
 if((DHT.temperature < 23) && (DHT.temperature > 20.2)) {
 digitalWrite(grnPin, HIGH); // green
 delay(100);
 digitalWrite(redPin, LOW);
 digitalWrite(bluPin, LOW);
 }
 if((DHT.temperature < 20) && (DHT.temperature > 17.2)) {
 digitalWrite(grnPin, HIGH); // aqua
 digitalWrite(bluPin, HIGH);
 delay(100);
 digitalWrite(redPin, LOW);
 }
 if(DHT.temperature <= 17) {
 digitalWrite(bluPin, HIGH); // blue
 delay(100);
 digitalWrite(grnPin, LOW);
 digitalWrite(redPin, LOW);
 }
 delay(1000);
 // Sensor shouldn't be read too frequently so delay of 1s
}

I will be grateful if I can get some help. Thanks!

• Mikael Patel: Add Serial.print() in each block that sets the pins to new values.

Answer 1

So far I only get 1's and 0's

Before moving into the LED parts, you have to make sure that your system can correctly read the DHT sensor. There are debugging example from arduino-info.wikispaces.com

How can I change these integer values to output string say RED, GREEN or BLUE?

You can do it by simple if-else statement. This would be better than your original code, because there are multiple if's without any else which is (although not so significant) less optimal.

So, if put together, you can try:

void loop()
{
 int t,h,chk = DHT.read11(DHT11_PIN);
 switch (chk)
 {
 case DHTLIB_OK: 
 Serial.print("OK,\t"); 
 break;
 case DHTLIB_ERROR_CHECKSUM: 
 Serial.print("Checksum error,\t"); 
 break;
 case DHTLIB_ERROR_TIMEOUT: 
 Serial.print("Time out error,\t"); 
 break;
 case DHTLIB_ERROR_CONNECT:
 Serial.print("Connect error,\t");
 break;
 case DHTLIB_ERROR_ACK_L:
 Serial.print("Ack Low error,\t");
 break;
 case DHTLIB_ERROR_ACK_H:
 Serial.print("Ack High error,\t");
 break;
 default: 
 Serial.print("Unknown error,\t"); 
 break;
 }
 //moving on into next parts only if you get "OK" from serial reply, which means you successfully read the DHT11
 t = DHT.temperature;
 h = DHT.humidity;
 Serial.print(DHT.humidity, 1);
 Serial.print(",\t");
 Serial.println(DHT.temperature, 1);
 //----end of sensor reading and debugging
 if (t<=17)
 { //blue
 digitalWrite(bluPin, HIGH); 
 digitalWrite(grnPin, LOW); 
 digitalWrite(redPin, LOW); 
 delay(100);
 } else
 if (t<20)
 {
 digitalWrite(grnPin, HIGH); // aqua 
 digitalWrite(bluPin, HIGH); 
 digitalWrite(redPin, LOW); 
 delay(100); 
 } else
 if (t<23)
 {
 //.... 
 }
 //....
 //and goes on
 delay(1000); 
}

And yes, as @Matt suggest, it would be better if you use PWM to control the RGB led which will give you (mathematically) 255*255*255 colour possibilities instead of 8 combinations from digitalWrite(). For example:

//....
//....
 if (t<20)
 { //aqua
 new_t = map(t,DHT11_min_temperature_reading,DHT11_max_temperature_reading,0,255);
 //you can do self research about DHT11 maximum and minimum temperature reading
 //parameters 0 and 255 is the minimum value of PWM(0) and the maximum value(255)
 AnalogWrite(bluPWMPin, new_t); 
 AnalogWrite(grnPWMPin, 255-new_t); 
 AnalogWrite(redPWMPin, 0); 
 delay(100);
 }
//....
//....

Hope it helps :D

Answer 2

You need to use analogWrite(). You use this with a digital pin and it does Pulse Width Modulation (PWM) which will give you are larger range of colours. Have a look at the Reference page for the function.

You might even be able to use the map function (something like that) to 'map' the temperature to the colour values without all the if statements.

• Gerben: The PWM pins have a ~ next to them on the PCB.
• Ekom: Thanks for your response. Do you have an idea of how I can implement the map function?
• Code Gorilla: Erm... not a clue, I've never used it, but I have seen it on here.