Sensirion SHT11 with a PIC16F628-20

[adamchapman]

I'm using the above code with a 16f84a and getting a consistent number, which is clearly wrong. I'm getting humvalue 16003 and tempval 4000. And since I haven't burst into flames this seems unlikely to be accurate.

I also tried using a modified Keunyoung Oh's code for the 16f877 (found http://itp.nyu.edu/physcomp/sensors/Code/SHT11 ) but received similar results (consistent & wildly inaccurate numbers), though with different numbers.

Any idea why this might be?

Also, as a possible explanation: I'm using the DIP sht11 which has a 117 on the sensor. I'm assuming I should use the pin diagram which goes with sensirion sht11 sensor module #28018, but all the other pin diagrams are different.

any suggestions would be helpful.

thanks,
Adam

[adamchapman]

here's the full code I'm currently (trying to use) everything compiles and publishes in PBP, but still no good data. is my code messed up?

'*******************************[ SHT11 Sample Code ]********************************
' File...... SHT11.bas
' Purpose... SHT11 digital humidity sensor sample code
' MCU....... Microchip PIC16F877
' Software.. Converted to Proton+ 2.0 from PBPro ver 2.4
' Author.... Brandon Tarr
' E-Mail.... [email protected]
' Web....... http://www.spectrumedix.com
' Started... May 15, 2002
' Updated...
' Version... 1.0
'************************************************* *************************

'device 16f884a

DEFINE xtal 4
Define LCD_DREG PORTD
Define LCD_DBIT 4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG PORTE
Define LCD_EBIT 1

TEMP con 1
HUMI con 2
' adr command r/w
Symbol statusregw = $06 ' 000 0011 0
Symbol statusregr = $07 ' 000 0011 1
Symbol measuretemp = $03 ' 000 0001 1
Symbol measurehumi = $05 ' 000 0010 1
Symbol resett = $1e ' 000 1111 0

' -----[ Variables ]---------------------------------------------------------------------
ledPin             var     PORTB.0
ledVar var byte

rxPin              var     PORTB.3
txPin              var     PORTB.2
SCK var PORTA.4 ' SHT11 SCK
SDATA var PORTB.1 ' SHT11 DATA

i  var byte
f var byte
value var byte
errorr var bit
mode var byte
ack var bit

vall var byte
pktvalue var word
pktchksum var byte

humival var word
tempval var word
dewpoint var byte
checksum var byte

' -----[ Initialization ]----------------------------------------------------------------
'ADCON1 = 7 ' Set PORTA and PORTE to digital
'Low PORTE.2 ' LCD R/W line low (W)
Pause 500 ' Wait for LCD to start
'lcdout $fe, 1

' -----[ Main Code ]---------------------------------------------------------------------
usetheSHT11:
    SerOut2 txPin, 16468, [" ", 10, 13]
    High ledPin          ' Turn on LED connected to PORTB.0
    Pause 500       ' Delay for .5 seconds
    Low ledPin           ' Turn off LED connected to PORTB.0

    gosub connectionreset
    value = measurehumi
    gosub measure ' measure humidity
    humival = pktvalue * 1000
    humival = DIV32 4095
    'lcdout $fe, 2, " ", $fe, 2, "Humidity: ", dec humival / 10, ".", dec humival // 10, "%"
    value = measuretemp
    gosub measure ' measure temperature
    tempval = pktvalue * 1000
    tempval = DIV32 16383
    'lcdout $fe, $c0, " ", $fe, $c0, "Temperature: ", dec tempval / 10, ".", dec tempval // 10, 223, "C"
    SerOut2 txPin, 16468, ["humival  ", DEC humival, 10, 13]
    SerOut2 txPin, 16468, ["tempval  ", DEC tempval, 10, 13]

    pause 500 '100 decrease sample time
goto usetheSHT11

' -----[ Subroutines ]-------------------------------------------------------------------
connectionreset:
' communication reset: DATA line is high and at least 9 SCK cycles followed by transstart
' ________________________________________ _____
' SDATA: |_____|
' _ _ _ _ _ _ _ _ _ __ __
' SCK: _| |_| |_| |_| |_| |_| |_| |_| |_| |___| |__| |___
    input SDATA
    high SDATA
    low SCK ' set initial state
    for i = 1 to 9 ' 9 SCK cycles
    high SCK
    low SCK
    next
    gosub transstart ' transmission start
return

transstart:
' generates a transmission start
' ___ _____
' SDATA: |_____|
' __ __
' SCK: __| |__| |___

    high SDATA
    low SCK ' set initial state
    high SCK
    low SDATA
    low SCK
    high SCK
    high SDATA
    low SCK
return

measure:
' makes a measurement (humidity/temperature) with checksum
    errorr = 0
    gosub transstart ' transmission start
    gosub writebyte
    for i = 1 to 255 ' wait until sensor has finished the measurement
        if SDATA = 0 then
            goto meascomplete
    endif
    pause 1
    next
meascomplete:
    if SDATA != 0 then ' or timeout (~2 sec.) is reached
        errorr = 1
    endif
    ack = 1
    gosub readbyte ' read the first byte (MSB)
    pktvalue.highbyte = vall
    gosub readbyte ' read the second byte (LSB)
    pktvalue.lowbyte = vall
    ack = 0
    gosub readbyte ' read checksum (no acknowledge to put sensor in "sleep" mode)
    pktchksum = vall
return

writebyte:
    ' writes a byte on the Sensibus and checks the acknowledge
    errorr = 0
    i = $80
    while i > 0
        if (i & value) != 0 then ' masking value with i
            high SDATA ' write to SENSI-BUS
        else
            low SDATA
        endif
        high SCK ' clk for SENSI-BUS
        low SCK
        i = i / 2 ' shift bit for masking
    wend
    high SDATA
    TRISB.1 = 1 ' release SDATA-line
    high SCK ' clk #9 for ack
    errorr = SDATA ' check ack (SDATA will be pulled down by SHTXX)
    low SCK
return

readbyte:
' reads a byte from the Sensibus and gives an acknowledge in case of "ack=1"
    vall = 0
    high SDATA
    TRISB.1 = 1 ' release SDATA-line
    i = $80
    while i > 0
        high SCK ' clk for SENSI-BUS
        if SDATA = 1 then ' read bit
            vall = vall | i
        endif
        low SCK
        i = i / 2
    wend
    TRISB.1 = 0 ' grab SDATA-line
    SDATA = ack ' in case of "ack", pull down DATA-Line
    high SCK ' clk #9 for ack
    low SCK
    high SDATA
    TRISB.1 = 1 ' release SDATA-line
return

softreset:
' resets the sensor by a softreset
    errorr = 0
    GOSUB connectionreset ' reset communication
    value = resett
    gosub writebyte ' send RESET-command to sensor
return

[tonyfelloni]

Hmmmm. This was a valid interesting topic.... pity it ends in the middle of nowhere without a solution!

[skimask]

Hmmmm. This was a valid interesting topic.... pity it ends in the middle of nowhere without a solution!

I think there are a couple of other working examples somewhere here on the forums.
And heck, if the original poster doesn't care if the problem is solved, why should anyone else?

[tonyfelloni]

Hey Skimask

I care because its relevant to something I am working on now.... To find the perfect thread....only to discover you have been led up the garden path, haha. Not to worry, I did see a few other relevant posts elsewhere.

Cheers
Tony

[psenek]

Hi!

I know this is an old thread but this might still help someone.

NavMicroSystems' example works fine, if you place wx=wy<< bt+(bt & wx.bit15)
instead of wx=(wy< Next.

It has some issues with negative temperatures but ok...

It's important that you don't forget 10k pullup on DTA line.

There's one more thing: you should replace all HIGH dta
commands with INPUT dta.

Datahseet SHT1x @ page 5.

"To avoid signall contention the microcontroller must only
drive DATA low".

When you have appropriate (10k) pullup on dta the line
goes high if you set the dta pin to input. I tested it and
it works perfectly fine.

Also: if this is your first attempt to communicate with SHT1x maybe
you should consider omitting dewpoint calculations and just read
raw data.

For room ambient (i had about 22°C and 35 %RH when testing) you should
get readings like 0x1855 for 14bit temperature and 0x03EE for 12bit humidity).

Best regards,

Rok

[yohanfx]

I want to program SHT11, with language PBP or Pbasic
want to know the temperature and humidity with SHT11.
please help me ....

[iw2fvo]

Hi ,
I am going to implemant the dew point computation with this sensor and with a PIC badìsic Pro.
I agree that there is an errot in DP calculation when the temperature is under 0°C.
Any help to solve the problem? Or any updated code ?
Thanks for helping.
Regards,
Ambrogio

Hi!

I know this is an old thread but this might still help someone.

NavMicroSystems' example works fine, if you place wx=wy<< bt+(bt & wx.bit15)
instead of wx=(wy< Next.

It has some issues with negative temperatures but ok...

It's important that you don't forget 10k pullup on DTA line.

There's one more thing: you should replace all HIGH dta
commands with INPUT dta.

Datahseet SHT1x @ page 5.

"To avoid signall contention the microcontroller must only
drive DATA low".

When you have appropriate (10k) pullup on dta the line
goes high if you set the dta pin to input. I tested it and
it works perfectly fine.

Also: if this is your first attempt to communicate with SHT1x maybe
you should consider omitting dewpoint calculations and just read
raw data.

For room ambient (i had about 22°C and 35 %RH when testing) you should
get readings like 0x1855 for 14bit temperature and 0x03EE for 12bit humidity).

Best regards,

Rok