DHT11 Precision

Other Hardware Sensors
1

Hey people, are you ok ? I hope so !

I have a DHT11 Module sensor and there is a very big difference in the measured values.

For example:

Humidity: 17% when it is 93% actually.

Temperature: 21 C when it's actually 13.

Is there any way to get closer?

Here is my current sketch:

#include "DHT.h"

#define DHTPIN A1 // pino que estamos conectado
#define DHTTYPE DHT11 // DHT 11

DHT dht(DHTPIN, DHTTYPE);

void setup()
{
Serial.begin(9600);
Serial.println("DHTxx test!");
dht.begin();
}

void loop()
{
float h = dht.readHumidity();
float t = dht.readTemperature();

if (isnan(t) || isnan(h))
{
Serial.println("Failed to read from DHT");
}
else
{
Serial.print("Umidade: ");
Serial.print(h);
Serial.print(" %\t");
Serial.print("Temperatura: ");
Serial.print(t);
Serial.println(" *C");

delay(5000);
}

}

temp_hum.ino (578 Bytes)

2

The best way to get better readings is to get a halfway decent sensor. The DHT11 can hardly be called a toy, it's pretty hopeless. Even the DHT22 will give you much better results, and then of course there are the venerable BME280 for humidity and pressure, and the DS18B20 for temperature..

3

DHT 11:

Relative Humidity
Resolution：16Bit
Repeatability：±1%RH
Accuracy：25℃ ±5%RH
Interchangeability：Fully interchangeable
Response time：1/e (63%)25℃ 6s
1m/s Air 6s
Hysteresis：<±0.3%RH
Long-term stability：<±0.5%RH/yr

Not really very good considering a RH of 75% can read anywhere between 70% & 80% and be in tolerance. If you want to be able to check sensors of RH for accuracy learn about Saturated Salt solutions for RH.

"Humidity: 17% when it is 93% actually".

How were you measuring the 93%?

Ron

4

Just realised that 93% humidity is out of range of what the DHT11 can measure, which is 20-90%.