README.md

Sekdiy SensirionSHT Library

Purpose

SensirionSHT is an Arduino library that provides easy, non-blocking access to Sensirion SHT1x temperature and humidity sensors (and compatible).

Simple Example

SensirionSHT works completely non-blocking:

void loop() {
  // update measurement
  Sensor.tick(delayTimeInSeconds);

  // new values should occur every three seconds
  Serial.println(Sensor.getTemperature());

  //
  // any other code can go here
  //

  // delay expects milliseconds
  delay(delayTimeInSeconds * 1000);
}

In the above example, an object Sensor is assumed. This Sensor is updated periodically (every delayTimeInSeconds). The calls to Sensor are completely non-blocking, i.e. they return immediately.

See the Simple example (included with this library) for the complete code.

Multiple Sensors Example

You could even use multiple sensors (connected to their respective clock and data pins):

// create a couple of SensirionSHT instances
SensirionSHT Sensor1 = SensirionSHT(1, 2);
SensirionSHT Sensor2 = SensirionSHT(3, 4);
SensirionSHT Sensor3 = SensirionSHT(5, 6);
...
// update them all
Sensor1.tick(duration);
Sensor2.tick(duration);
Sensor3.tick(duration);

Synchronous Example

The library provides a way to use sensors and other code synchronously. Here's another example:

void loop() {
  // track current time
  float currentTime = millis() / 1000.0f;
  float duration = currentTime - lastTime;

  // synchronous block, executed every period
  if (duration >= period) {

    // prepare for next cycle
    lastTime = currentTime;

    // update measurement
    Sensor.tick(duration);

    // check for valid temperature data
    if (Sensor.hasTemperature()) {
      Serial.print("current temperature: ");
      Serial.print(Sensor.getTemperature());
      Serial.println("°C");
    }

    //
    // anything that should run periodically goes here
    //
  }

  //
  // anything else goes here
  //

}

The SHT series can take a couple hundred milliseconds per measurement (with it's settling time more in the order of seconds, anyway).

So each of the calls to Sensor is actually just checking for arrival of a signal, keeping the program from spinning while waiting for the sensor.

See the Synchronous example (included with this library) and maybe also the IrrigationController project (where this library is being used with a scheduler, timers, interrupt handlers, real-time clock, etc.) for more.

Installation

Just check out the SensirionSHT Repository on GitHub (or download the ZIP archive) and copy it to your libraries/ folder (usually within your Arduino sketchbook).

Now do the same with the Sensirion library by Markus Schatzl and Carl Jackson, since SensirionSHT extends (and thus requires) it.

After (re)launching the Arduino IDE, SensirionSHT (as well as Sensirion) will appear in your Sketchbook/Examples menu.

Alternatively, you can use Arduino's Add .ZIP Library... menu option.

Calibration

These sensors come pre-calibrated, the manufacturer provides a certificate. Nevertheless, depending on the intended application it never hurts to check individual sensor accuracy before relying on it.

I'm currently working on a tool that supports sensor calibration and linearisation. Until then, I recommend Robert J. Smith's thorough comparison of various hygrometers. He also provides a detailed explanation how to calibrate such a sensor.

Documentation

There's a copy of the SHT1x datasheet from Sensirion in the folder doc/.

Additionally, the library contains a folder doc/doxygen/ for html documentation generated via Doxygen (with some adaptions by Velron).

In order to generate this documentation yourself, simply execute doxygen doc/doxygen/Doxyfile from within the main library folder SensirionSHT/.