The cased protoype showing the balmy conditions inside my house, summer 2003.
The Sensor
This uses the combined
humidity and temperature sensor SHT11 from
Sensirion.
The SHT11 is in a SMD package,
while the SHT71 is a SIL 4 pin version.
The specifications for both are the
same.
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The SHT11 sensor, soldered
to some SMD proto
board |
The double sided PCB has been designed
to allow the more easily obtainable handy
8pin DIP carrier version to be used.
The sensor contains a 14 bit analog to
digital converter for temperature conversion
resulting in a maximum resolution of 0.1 °C
spanning -40 to 123.8, while the humidity sensor
uses a resolution of 12 bits (0.03%RH) with a
range of 0 to 100%RH. Note that there is a maximum
deviation of ± 3% between 10-90%
RH.
The controller project is made up of
three parts. Click on the title to view the
text
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Controller
board
reads the sensor, updates the
LCD display, reads the rotary encoder,
switches the outputs.
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AC Control board
g ives you the option of housing
the power transformer and one switched AC
output. If the AC output is used, this takes the
place of the heater DC
output.
If you just require temperature and
humidity readings, the controller board can be
used as a stand alone concept.
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