Sht4x

[pedja089]

Does anyone have SHT40 example code?
I'm trying for 2 days, and no progress. Is it posible with i2cwrite, i2cread command?
Trying to do conversion and read data, all 0's. Trying to read serial no, al 0's.
HW connection looks good.

[richard]

what have you tried ?
i fumbled around a bit with a scd41 which has a similar modus operandi and managed to get it to work with i2cread/write commands eventually , trick was to send a dummy 0 write prior to the needed delay before the result was read back

[pedja089]

Got it working, stupid datasheet....
Address is $88, not $44, as in datasheet.
Found that using
https://www.picbasic.co.uk/forum/sho...C-Ping-program
Then is straight forward
1. Read serial

SHTAdr=$88
SHTCmd=$89
I2CREAD S_SDA1,S_SCL1,SHTAdr,SHTCmd,[SHTArray[0],SHTArray[1],SHTArray[2],SHTArray[3],SHTArray[4],SHTArray[5]]

0-1 serial 1 word, 2 crc, 3-4 serial 2 word, 5 crc
2.Start conversion

SHTAdr=$88
SHTCmd=$FD
I2CWRITE S_SDA1,S_SCL1,SHTAdr,SHTCmd,SensorFailNoAck

3. Read Temp and RH data after 20mS

SHTAdr=$88
I2CREAD S_SDA1,S_SCL1,SHTAdr,[SHTArray[0],SHTArray[1],SHTArray[2],SHTArray[3],SHTArray[4],SHTArray[5]]

0-1 hold temp, 2 hold crc, 3-4 hold humidity, 5 hold crc.
If I add SensorFailNoAck, then it trigers every time, not sure why... I'll use crc to check for correct communication.
CRC8 routine:

CalcCRC:
crc=$ff
 for byteCtr = 0 to 1
    TmpB=CRCArray[byteCtr]
    crc  = crc ^ TmpB
    for  i = 0 to 7
        if crc.7=1 then
            crc = (crc << 1)
            crc =  crc ^ $31
        else
            crc =crc << 1
        endif
    next i
 next byteCtr

Need to check calculation from ticks to T[°C] and RH[%].
And to try to understand heater... How and why to use it.