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Hi! I'm using MSP430I2020's analog-to-digital converter in single ended configuration to read two analog voltages from a sensor.
I've connected the sensor outputs to A0.0+ and A1.0+, respectively. A0.0- and A1.0- are connected to GND. This is the code I'm using:
void SD24_initialize(void)
{
// Internal ref
SD24_init(SD24_BASE, SD24_REF_INTERNAL);
//Group with Channel 0
SD24_initConverterAdvancedParam param = {0};
param.converter = SD24_CONVERTER_0;
param.conversionMode = SD24_CONTINUOUS_MODE;
param.groupEnable = SD24_GROUPED;
param.inputChannel = SD24_INPUT_CH_ANALOG;
param.dataFormat = SD24_DATA_FORMAT_2COMPLEMENT;
param.interruptDelay = SD24_FOURTH_SAMPLE_INTERRUPT;
param.oversampleRatio = SD24_OVERSAMPLE_256;
param.gain = SD24_GAIN_1;
SD24_initConverterAdvanced(SD24_BASE, ¶m);
//Group with Channel 1
param.converter = SD24_CONVERTER_1;
param.conversionMode = SD24_CONTINUOUS_MODE;
param.groupEnable = SD24_NOT_GROUPED;
param.inputChannel = SD24_INPUT_CH_ANALOG;
param.dataFormat = SD24_DATA_FORMAT_2COMPLEMENT;
param.interruptDelay = SD24_FOURTH_SAMPLE_INTERRUPT;
param.oversampleRatio = SD24_OVERSAMPLE_256;
param.gain = SD24_GAIN_1;
SD24_initConverterAdvanced(SD24_BASE, ¶m);
// Enable interrupt
SD24_enableInterrupt(SD24_BASE, SD24_CONVERTER_1, SD24_CONVERTER_INTERRUPT);
// Delay ~200us for 1.2V ref to settle
__delay_cycles(3200);
}
void SD24_read(float* op1, float* op2)
{
// Start conversion
SD24_startConverterConversion(SD24_BASE, SD24_CONVERTER_1);
// Enter LPM0 w/ interrupts
__bis_SR_register(LPM0_bits | GIE);
SD24_stopConverterConversion(SD24_BASE, SD24_CONVERTER_1);
for (i = 0; i < NUM_OF_RESULTS; i++)
{
Ch0results_float[i] = Int24BitTwoComplementToSignedInt(Ch0results[i]) * LSB * 2.0;
Ch1results_float[i] = Int24BitTwoComplementToSignedInt(Ch1results[i]) * LSB * 2.0;
}
if (NUM_OF_RESULTS > 1) // Mean value
{
float sum0 = 0, sum1 = 0;
for (i = 0; i < NUM_OF_RESULTS; i++)
{
sum0 += Ch0results_float[i];
sum1 += Ch1results_float[i];
}
*op1 = sum0 / NUM_OF_RESULTS;
*op2 = sum1 / NUM_OF_RESULTS;
}
else
{
*op1 = Ch0results_float[0];
*op2 = Ch1results_float[0];
}
}
int32_t Int24BitTwoComplementToSignedInt(uint32_t val)
{
return (0x800000 & val ? (int)(0x7FFFFF & val) - 0x800000 : val);
}
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=SD24_VECTOR
__interrupt void SD24_ISR(void) {
#elif defined(__GNUC__)
void __attribute__ ((interrupt(SD24_VECTOR))) SD24_ISR (void) {
#else
#error Compiler not supported!
#endif
switch (__even_in_range(SD24IV,SD24IV_SD24MEM3)) {
case SD24IV_NONE: break;
case SD24IV_SD24OVIFG: break;
case SD24IV_SD24MEM0: break;
case SD24IV_SD24MEM1:
// Save CH0 results (clears IFG)
Ch0results[i] = SD24_getResults(SD24_BASE, SD24_CONVERTER_0);
// Save CH1 results (clears IFG)
Ch1results[i] = SD24_getResults(SD24_BASE, SD24_CONVERTER_1);
i++;
if (i == NUM_OF_RESULTS) {
i = 0;
__bic_SR_register_on_exit(LPM0_bits); // Wake up
}
break;
case SD24IV_SD24MEM2: break;
case SD24IV_SD24MEM3: break;
default: break;
}
}The values read by the ADC are half than those measured with a voltmeter. So I've multiplied them with 2.
My questions: is it expected for SD24 to return half values when working in single ended configuration, with 2's complement output format? Am I reading the values correctly?
Hello,
The SD24 will return a value that's between +Full Scale Range (FSR) and -FSR. Since you're using a gain of 1, the +/-FSR is +/-928mV. However, your input circuitry (probably voltage dividers) will impact how much of that FSR you're using at the maximum input voltage. Ideally, you'd want to use the full range. Basically, what you're seeing is normal, but you'll need to calibrate the device.
Let's assume the device measures an input voltage within +/-FSR. However, this isn't in human terms, but MCU terms. Thus, you need to calibrate it at a certain known input voltage, which would allow you to calculate the necessary scaling factor that translates the MCU results (e.g. 0x1234) into human results (e.g. 3300mV).
Does this make sense?
Regards,
James
MSP Customer Applications
Where did you find this function? After a quick glance, it appears to be fine. Is your input voltage 220mV? Could it vary? Is it AC or DC? What do you get BEFORE multiplying the result with LSB? Can you try inputting a known positive voltage from a signal generator? Connect its positive and negative outputs to the SD24 +/- inputs.
Based on the MSP430 portion of your schematic (found in the thread below), I'd recommend removing the diodes and shorting the in-line resistors too. What's the sensor that you're measuring?
MSP432P401R: Problem with I2C pullups - MSP low-power microcontroller forum - MSP low-power microcontrollers...
Part Number: MSP432P401R
Hi! I'm using MSP432 (master) to communicate with some MSP430I2020s over I2C (up to 8 slaves - sensors). The problem is that the high
Regards,
James
MSP Customer Applications
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