Tuesday, June 17, 2008

SHT75/SHT15 Sensors tested



Found some time last weekend to test out the latest release of butterflylogger with an SHT75 sensor from www.sensiron.com, which I bought from Farnell. I haven't had one of these for testing since I destroyed my last one back in 2004.

The first thing I noticed was a very unusual looking clock signal when talking to the sensor. Although this did not seem to bother the SHT75 I decided to fix it for a more robust interface.

I also decided to add a command to output the current readings for temperature and humidity from the device via the serial interface. "J" and "j" will print the hex values for temperature and humidity respectively.

I have also added the ability to do the real world conversions on the logger. If you have the code space (ie. have disabled the LCD, joystick and menu system) you can have the device log the actual temperature and relative humidity. If you are also logging the batter voltage, the logger will read the battery voltage and use this in the conversion interpolating values from the table given in the data sheet for 'D1' (see page 5).

The overhead of adding the realworld values is about 800 bytes and using the battery voltage as well a further 200 bytes. If your looking to save space then this is probable code you would wnat to disable. In Sht.h there is a #define ENABLE_SHT_CALCS which can be commented out to revert to the old behaviour of simple hex values being logged and real world conversions being done on the host PC post logging.

Supose now I'd best get back to finishing my construction pages for the mp3 player

2 Comments:

At 11:58 AM, Blogger sahand said...

Hi. Just curious, which digital analyzer are you using for the above signal diagrams?

 
At 7:22 PM, Blogger Nick said...

Hi Sahand,

I use a logicport from intronix at http://www.pctestinstruments.com/

Its fantastic.

 

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