Other Parts Discussed in Thread: MSP430FR6989
Hi,
We are trying to get to the bottom of an issue that have troubled us for a while.
Our System is built around a msp430fr5989.
We use the ADC12B module of the MCU along with a thermistor from Murata to monitor ambient temperature.
We also use the external PCF8523 RTC from NXP to provide a coin cell backed-up time keeping source.
This external RTC gives us also a 32.768kHz clock that we use to provide an external clock to our MCU msp430fr5989.
We use the internal reference voltage of 1.2V for VRef+ and verify its value at the
P1.1 pin.
The transfer function of the Murata Thermistor is very linear in the temperature range 0-40 degrees Celsius.
The code to read the raw values from the ADC12-B is based on the sample code OutOfBox_MSP430FR6989.
From there we stripped all the code not related to the temperature sensor.
The voltage read at the TP7 (see snippet of Schematics below)
is converted in theoretical ADC counts by the use of the Thermistor Transfer Function
( see our Excel document for the transfer function)
The ADC counts we get at ADC12MEM0 gives us a temperature that is about 3 degrees Celsius off from the one obtained by converting the voltage we read at TP7.
We have experimented with various clock settings and calibration recommendations.
We cannot, however, figure out what is off in our approach.
I am joining to this note the code we have been using for this validation along with the Thermistor transfer function.
Your help in resolving this issue would be indeed greatly appreciated.
MightyPuffer Thermistor_Trimmed.xlsm.zip