SHT 11 DataSheet
Connection between SHT-11 and weather station:
SHT11 pin GND X4-2 DATA X3-2 CLOCK X4-1 +5V X3-1
(printed on the circuit board too)
Eagle 4.03 (displayed bitmap may not give the accurate dimensions)
(there is a 100n cond. connected between GND and +5V on the sensor board
and +5V is secured by 1N4148 diode to prevent incorrect power supply connection)
Part Value
C1 100n
C2 100n
C3 33u
C4 100n
C8 470p
D1 1N4148
IC1 78L05
IC3 PIC12F675P
IC7 LM2904N
JP1 jumper
JP2 jumper
MPX1 MPX4115
R1 10k
R2 330
R3 100K
R6 9k1 1%
R7 8k2 1%
R8 10k 1%
R9 10k 1%
R10 2k2
R11 4k7 1%
R12 1k8 1%
R13 4k7 (pull-up rezistor for DATA signal SHT-11)
X1 W237-02P (screw connector 2pin/5mm)
X2 F09H (Canon 9 female to PCB)
X3 W237-02P (screw connector 2pin/5mm)
X4 W237-02P (screw connector 2pin/5mm)
SHT-11 temperature and humiditi sensor made by Sensirion
Otherwise Power supply could by from 7 to 30V.
A glass of water closed only by a pice of textil gives aprox. 90% humidity.
Value of R13 (4k7) is designed for 30-90cm long cable between WX and the sensor. If You get something like 8% humidity and -39.9C temperature You should try lower value of R13. If You get still only 1% humidity and -39.9C it is highly possible, that sensor does not communicate with WX station or the sensor is broken.
In the measurement mode (both jumpers are open) wx station is sending (every 5 seconds) to the RS-232 output APRS WX data string in following format: <Esc>w000/000g000tnnnbnnnnnhnn<CR>znnnC
where nn are measured values
and z is sign "-" for temperature below zero Celsius degree or space for temperature above zero Celsius
In configuration mode (JP2 is closed) wx station accepts following commands:
^U - upload EEPROM to RS-232 port
^D - download EEPROM - writes following bytes to EEPROM (there must be a delay min. 80ms between bytes)
^M - measures once and returns standard string to the RS-232, if You open JP2 during measurement (aprox. 5s) wx station leaves configuration mode and enters measurement mode. Otherwise it continues in configuration mode.
Configuration mode is indicated by ">" prompt
^ is ESC character
For download EEPROM contents and upload back into processor's EEPROM use of Piceerw program is recomended. full installation 1.4MB; exe only, needs ocx libraries (36kB)).
The only thing which needs to be configured is pressure. MPX 4115 measures absolute pressure. So You need to add a constant value which depends on the above see level on Your location. This value is stored in processor's EEPROM from address 0Fh to 12h (4 bytes) and it is a number in FLO32 format. For conversion the number to FLO32 format You can use Fprep.exe program.
The value for calibration You may count by storing four 00h on addresses 0Fh to 12h in EEPROM, measure the pressure and compare it with pressure supplied by weather service in Your region. Difference is the needed value. Multiply this value by 10 (value in EEPROM is expected to be in tens of hectopascals), convert it to FLO32 and write it to the file with EEPROM data. Write this file back to EEPROM and You should receive right pressure from now.