The SHT11 sensor measures relative humidity and temperature. It connects via 2 I/O lines using an I2C’ish protocol with a funny (optional) CRC check. I’ve hooked it up to port 1 on a JeeNode:
There are just four wires to connect to this minute module. Here’s a close-up, with data and ground crossed over to port pins 2 and 3, respectively:
The sensor is mounted free-floating on this little DIY breakout board so it picks up ambient air properties.
A driver for the SHT11 has been added to the Ports library, along with a small demo:
A “sensor” object is defined at the top, tied to a specific “port” – the SHT11 class is derived from the Port class.
Sample output:
The driver uses PROGMEM for the optional crc table. This causes a warning in Arduino-0013 when switching boards (which recompiles PortsSHT11.cpp), probably due to this issue, i.e. gcc bug #34734.
With thanks to Guido Socher for his excellent page about the SHT11 (his version does all calculations using fixed point integers, if you prefer to avoid floats).
Update – Changes checked-in and ZIP file updated. Thanks to Stephen Eaton for pointing out a mistake in the calculation constants for 3.3V.