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AD7147-1 Capacitive Result Wrong on I2C Read

Question asked by retti on Aug 12, 2015
Latest reply on Sep 8, 2015 by DarraghCorrigan



I hope someone can help me on this issue:

I got a problem with reading the CDC_RESULT_S*, there are sometimes wrong results read back from the sensor.


The PCB includes 3 AD7147-1, in summary i use 36 capacitive electrodes to measure a binary code (cupper lines on the other side)

to reduce the noice and interference i enable only one sensor at one time (POWER_MODE = full power mode OR full shutdown mode)

then i wait (continous read register) for one of the Bits in STAGE_COMPLETE_INT_STATUS to become 1, if that happend i read the corresponding CDC_RESULT_S* which result in a wrong value ( for example 0xFFFF instead of about 37000 )


i attached some pictures to illustrate two failure reads during read of 200 x 12 x 3 values (while nothing changed in the HW-settings)

And second a communication capture (bit-bang I2C) on a wrong Result Read, maybe someone can give me a hint on this issue.

cdc 2 fails on 200x36 values.jpg




read 0x0A = INT-Status -> get 0x80 = STAGE 11 complete  --> read CDC_RESULT_S11 -> get 0xFFFF which is absolutely wrongi2c failread5.png

i2c failread11.png



in detail:

i2c failread10.png


Thanks for your help