I2C communication with Honeywell HumidIcon RH sensor problem

[yinni]

Hello,

I posted my problem about the I2C communication between Kinetis K50 100MHz 100LQFP and Honeywell Humidlcon RH sensor several days ago. After testing SCL and SDA signals with oscilloscope, I just realized the sensor failed to acknowledge the address because the SDA line fluctuated between around VDD and VDD/2. In my program, the RH sensor receives a measurement command and a read command alternately for every 100ms. In general the signal rises to VDD after the write-bit (logic LOW) following the 7-bit address, whereas drops to about VDD/2 after the read-bit (logic HIGH) following the 7-bit address. Waveform of the SDA line fluctuation (with larger time scale), and detailed I2C SCL and impaired SDA signals are attached

My pull-up resistors are 2.2K as suggested by the datasheet, current drawn by the RH sensor is below 1mA during I2C communication. This same I2C interface ever worked well with Sensirion SHT35 sensor. Really couldn't figure out how to fix the problem, please help!

[mjbcswitzerland · Accepted solution]

Hi

- Have you correctly configured the I2C pins to open drain mode?
- mid voltage levels signal two devices driving the bus at the same time [one driving '1' and the other driving '0'] (identify what is unexpectedly driving the bus by removing parts or inserting a series 470R resistor in each line)

Regards

Mark