Maybe you need pull up resistors? The revision B of the Weather Cape also
uses a Sensirion humidity sensor SHT21:
http://elinux.org/CircuitCo:BeagleBone_Weather

-Hieu


On Tue, Jul 29, 2014 at 9:12 PM, Tatsuya Sasaki <tasas...@gmail.com> wrote:

> Hi all.
> I hooked up my sensirion SHT20 temp/humid sensor to my BBB.
>
> http://www.sensirion.com/en/products/humidity-temperature/humidity-sensor-sht20/
>
> -SHT20-  -BBB-
> GND ---> P9-01
> VDD ---> P9-03
> SCL ---> P9-19
> SDA ---> P9-20
>
> The datasheet says the address is 01000000 (0x40).
>
>> 5.3 Sending a Command
>> After sending the Start condition, the subsequent I2C
>> header consists of the 7-bit I2C device address ‘1000’000’
>> and an SDA direction bit (Read R: ‘1’, Write W: ‘0’).
>> The wiring is like the following.
>
>
> I expected to appear the sensor on I2C-1's address 0x40.
> But it isn't detected:
>
> $ sudo i2cdetect -r -y 1
>
>      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
>
> 00:          -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 50: -- -- -- -- UU UU UU UU -- -- -- -- -- -- -- --
>
> 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 70: -- -- -- -- -- -- -- --
>
> and also
>
> $ sudo i2cdetect -r -y 0
>
>      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
>
> 00:          -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 20: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- --
>
> 30: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- --
>
> 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 50: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
>
> 70: UU -- -- -- -- -- -- --
>
> I checked the sensor worked as a normal I2C device on my Arduino.
>
> Do I need to install some drivers on BBB for the sensor?
> Or do I missed some procedures?
>
> --
> For more options, visit http://beagleboard.org/discuss
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