Dear community,
I am a fresher to the TI community and exploring Rasberry Pi and TI products for simple data acquisition. I am trying to explain my questions to my best and please
let me know if there is any missing information
Scenario:
I am using 12-bit ADC (ADS7841) and temperature sensor (LM35) together with Raspberry pi (Model B) and dedicated SPI library interface to read the digital values.
The control bits sent:
1. first byte 1001 1100 and second as '0x00' for 8 bit
2. first byte 1001 0100 second and third as '0x00' for 12 bit
I read back and convert these bytes into decimal values using dedicated C functions.
I have these following questions in this regard:
1. Are the bit sent correct for the two cases: 8 bit mode and 12 bit mode?
2. Interpreting the ADC values read in 8 bit mode:
I converted the read digital value to analog voltage using: mV = (ADC digital value)*Vfref/255
When I looked the analog sensor table, LM35 for instance, the read mV vs sensor value, I see the read mV is exactly actually half the expected value: Hence the correct conversion should be mV = 2* (ADC digital value)*Vfref/255. How to justify this?
Twice the digital value correction is verified with a different analog sensor (LM61) as well.
3. How to know which of the cycles 24/16/15 the device (ADS7841) is under going or how to specify it? If this very fundamental that I need to know, can anyone share a link/post for a simple explanation.
Thanks,
Hariram