biogeo/sht1xalt

An "alternative" Arduino library for communicating with an SHT1x Sensirion temperature/humidity sensor

sht1xalt: An "alternative" Arduino library for the SHT1x sensor

Provides an interface to the SHT1x temperature / humidity series of sensors from Sensirion http://www.sensirion.com. I wrote this somewhat by accident when trying to debug errors that arose when I tried to both Jonathan Oxer's SHT1x library http://github.com/practicalarduino/SHT1x and Markus Schatzl's Sensirion library http://playground.arduino.cc/Code/Sensirion#Sensirion. If this library doesn't work for you, check out those!

Installation

Download the sht1xalt directory into the "sketchbook/libraries" directory, then restart the Arduino IDE. You can upload an example sketch to your Arduino from File->Examples->sht1xalt.

Usage

This library provides a class for managing interactions with the SHT1x, as well as several associated functions, constants, and datatypes. These are all provided within the sht1xalt namespace. If you're not familiar with namespaces, all you need to know is that all of the identifiers provided by the library need to be preceded by sht1xalt::, OR you can include the following line after the #include <sht1xalt.h> line in your sketch:

using namespace sht1xalt;

The only downside to the "using namespace" command is that if you also want to use another library in your sketch, and that library happens to use any of the same names that sht1xalt uses (e.g., "Sensor"), then you'll get errors. But if sht1xalt is the only library you're using, then there should be no trouble.

Typical usage of this library will consist of creating a global Sensor object to handle communication, configuring the interface in the setup() function, and calling measurement functions in the loop() function. So a typical sketch will look something like this:

#include <sht1xalt.h>
#define dataPin 10
#define clockPin 11
#define clockPulse 1
#define voltage sht1xalt::VOLTAGE_5V
#define units sht1xalt::UNITS_CELCIUS
sht1xalt::Sensor sensor(dataPin, clockPin, clockPulse, voltage, units);

void setup() {
  // Do some things
  sensor.configureConnection();
  sensor.softReset();
  // Do more things
}

void loop() {
  float temp;
  float rh;
  // Do some things
  sensor.measure(temp,rh);
  // Do more things
}

That will cover most use cases, but you can get fancy and do things like put the SHT1x in low resolution, low power consumption mode, or turn on the chip's heater to raise its temperature.

Features

• Read raw temperature and relative humidity values (great for logging or interfacing with a PC which can do the "hard" work of conversion)
• Read temperature in Celcius or Fahrenheit
• Read relative humidity as a percentage, without temperature compensation
• Read temperature and relative humidity together, with temperature compensation of the relative humdity (important if temperature is much different from 25 C or 77 F)
• Read/write the SHT1x's status register, allowing:
  • Toggling low resolution, low power consumption mode
  • Controlling the onboard heater
  • Controlling "OTP reload" (I don't know what this is, but if you do, you can set it!)
  • Querying the sensor's low voltage ("battery low") detector
• Set clock pulse width: longer pulses may help communication if the wires between the Arduino and the SHT1x are very long

Limitations

• CRC checksum isn't yet implemented
• The library is intended for easy use, not optimal speed or size. If you need to pack a lot of other code on your Arduino, many of the lookup tables could be replaced with hard-coded values for your setup (e.g., if you know the operating voltage, temperature units, and clock speed you need.) That said, a minimalist test sketch using this library gave me a sketch size of 6524 bytes (of a 30720 byte maximum) on my Duemilanova, so there's plenty of room for a lot more code still.