Monday, July 21, 2014

I2C RH Sensor 21May2014

This is a Relative Humidity and Temperature Sensor that attaches to the I2C Bus. It has a relative humidity accuracy of 3% a precision of .2% and a resolution of .1%. You can buy a higher accuracy version (2%) if you need it. Be sure to get the 5V version. For temperature the accuracy is .3°C and the precision is .01°C. There are two versions of the sensor. One is powered up continuously and the other just powers up for each reading. You can learn more by having a look at the family data sheet. The part number I tested the board with was the CC2D35. Any of the 5V parts in the family should work.

Soldering is not difficult (for surface mount). I normally mount the 4.7uF capacitors first and then mount the ICs. Mounting the TVS diode package before the capacitors and sensor is probably a good idea. The connector should get mounted last. You can get the parts list, schematic, and parts layout at I2C RH Sensor 21May2014 - Documentation. I also have software that will read out the sensor to 4 digits at I2C RH Sensor 21May2014 - Software For The LPC812 FISH Forth.txt. As you can tell it is designed to be run with our LPC812 board. The software is mainly a how to do it minimal package. Also note that the readout for this software is 4 digits (at room temperature and less than 100% relative humidity) with no decimal point. You can use other Forth routines to add a decimal point and add one more decimal place of resolution but I wanted to keep the software simple so it is easy to understand. For systems use you will probably want to add time outs and other things so a defective or missing sensor does not hang up the system.

This board is available from OSH Park for $3.05.

Engineering is the art of making what you want from what you can get at a profit.

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