Posted on December 10, 2016 at 15:09Few years back on STM32F437, got a sample code which might help. The coefficients are datasheet dependent.
Here the idea was to factor out the VDD supply of the ADC from the measurement.
Here is an extract of an old test code :) )
This code is only for guidance, not to be reused 'as is'.
Hope this helps.
s32 Interpolate_s32 (s32 x0, s32 x1, s32 y0, s32 y1, s32 x)
{
// code for 32 bit mcu
s32 dwQ;
dwQ = ((y1-y0))*x+(x1*y0)-(x0*y1); // overflow not checked yet
dwQ = dwQ / (x1-x0);// we can also do roundings here
return dwQ;
}
u32 ADC_Normal_LsbTo_mV(ADC_t* A, u32 Lsb) {
u32 mV = Interpolate_s32 (0, 0xFFF0, 0, A->VRef_mV, Lsb);
return mV;
}
u32 ADC_Injected_LsbTo_mV(ADC_t* A, u32 Lsb) {
u32 mV = Interpolate_s32 (0, (s32)0x7FF8, 0, A->VRef_mV, (s32)(s16)Lsb);
return mV;
}
u32 ADC_ConvertNormalTo_mV(ADC_t* A) {
u8 n;
for(n=0;n<countof(A->Normal_Lsb);n++) {
A->Normal_mV[n] = ADC_Normal_LsbTo_mV(A, A->Normal_Lsb[n]);
}
return n;
}
u32 ADC_ConvertInjectedTo_mV(ADC_t* A) {
u8 n;
for(n=0;n<countof(A->Injected_Lsb);n++) {
A->Injected_mV[n] = ADC_Injected_LsbTo_mV(A, A->Injected_Lsb[n]);
}
return n;
}
s32 ADC_Convert_mV_to_DegC_x10(ADC_t* A, u32 mV) {
s32 Deg30Lsb = (s32)(*((u16*) 0x1FFF7A2C));
s32 Deg110Lsb = (s32)(*((u16*) 0x1FFF7A2E));
// we first convert the LSB calibrated Flash values to mV (let's remove the sign issue between normal and injected channels)
u32 Deg30mV = Interpolate_s32 (0, 0x0FFF, 0, A->VRef_mV, Deg30Lsb);
u32 Deg110mV = Interpolate_s32 (0, 0x0FFF, 0, A->VRef_mV, Deg110Lsb);
u32 DegC_x10 = Interpolate_s32 (Deg30mV, Deg110mV, 300, 1100, (s32)(s16)mV);
A->Temp_degC_x10 = DegC_x10; // capture the value for debugging or reference
return DegC_x10;
}
s32 ADC_Convert_VRefByLsb(ADC_t* A, u32 Lsb) {
s32 VRefLsb3p3V_Lsb = (s32)(*((u16*) 0x1FFF7A2A)); // this contains the ADC 12 bit right aligned injected raw data for Vref LSB at 30C and 3.3V
u32 Vdd_mV = (3300*(VRefLsb3p3V_Lsb<<3))/Lsb;
A->MeasuredVdd_mV = Vdd_mV;
return 0;
}
s32 ADC_FeedbackVdd(ADC_t* A, u32 Vdd_mV) {
A->VRef_mV = A->MeasuredVdd_mV; // hmm....
return 0;
}
