Category: Hardware
Product Number: AD5941
Hi ADI Team,
I have tried using the AD5941 AFE to read open circuit potential of certain solutions but I have discovered that the analog pins that I am using for said measurement are heavily biased in the range of mV(using DMM) while the voltages I am trying to measure are in the range of microvolts, and hence the analog pins are biasing said solution and I am receiving erroneous readings.
I have the requirement to measure 5 different measurements wrt to a common reference so in total I need 6 pins and I have 3 AD5941 in my custom built PCB(heavily similar to the evaluation board)
Can I know why I am observing this behavior, will greatly appreciate your efforts to help me understand said issue.
Attached schematic to one of the AFE
The code I'm using is as follows
#include "ad5940.h"
#include <stdio.h>
uint32_t adc_pin[]={ADCMUXP_AIN1,ADCMUXP_AIN2,ADCMUXP_AIN3,ADCMUXP_AIN4, ADCMUXP_VAFE1};
uint32_t gain_val[]={10,20,50,100,200,500,1000};
#define ADCPGA_GAIN_SEL ADCPGA_1P5
static void AD5940_PGA_Calibration(void){
AD5940Err err;
ADCPGACal_Type pgacal;
pgacal.AdcClkFreq = 16e6;
pgacal.ADCSinc2Osr = ADCSINC2OSR_178;
pgacal.ADCSinc3Osr = ADCSINC3OSR_4;
pgacal.SysClkFreq = 16e6;
pgacal.TimeOut10us = 1000;
pgacal.VRef1p11 = 1.11f;
pgacal.VRef1p82 = 1.82f;
pgacal.PGACalType = PGACALTYPE_OFFSETGAIN;
pgacal.ADCPga = ADCPGA_GAIN_SEL;
err = AD5940_ADCPGACal(&pgacal);
if(err != AD5940ERR_OK){
Serial.println("AD5940 PGA calibration failed.");
}
}
float getVolt(uint8_t sz=10){
uint64_t rd=0;
float vlt=0;
uint8_t frq =sz;
while(frq>0){
if(AD5940_INTCTestFlag(AFEINTC_1,AFEINTSRC_SINC2RDY)){
AD5940_INTCClrFlag(AFEINTSRC_SINC2RDY);
rd = rd + AD5940_ReadAfeResult(AFERESULT_SINC2);
frq--;
}
}
vlt = (AD5940_ADCCode2Volt(rd/sz, ADCPGA_GAIN_SEL, 1.82));
return vlt;
}
void readVal(float *rd,float* t){
rd[4]=getVolt();
t[4] = (((float)millis())-t[5])/1000;
}
void print_float(float* a, long m=1){
int i=0;
while(i<5){
Serial.print(a[i]*m);
if(i==4&&m==1)
Serial.println();
else
Serial.print(" ");
i++;
}
return;
}
void reading(){
//float rd[5];
//float tim[6];
float rd[]={0,0,0,0,0};
float tim[]={0,0,0,0,0,0};
delay(100);
tim[5]=((float)millis())/1000;
while(1){
readVal(rd,tim);
print_float(rd,1000000);
print_float(tim);
//print_float(tim);
}
}
void AD5940_Main(void)
{
ADCBaseCfg_Type adc_base;
ADCFilterCfg_Type adc_filter;
/* Use hardware reset */
AD5940_HWReset();
/* Firstly call this function after reset to initialize AFE registers. */
AD5940_Initialize();
AD5940_PGA_Calibration();
/* Configure AFE power mode and bandwidth */
AD5940_AFEPwrBW(AFEPWR_LP, AFEBW_250KHZ);
/* Initialize ADC basic function */
AD5940_AFECtrlS(AFECTRL_DACREFPWR|AFECTRL_HSDACPWR, bTRUE); //We are going to measure DAC 1.82V reference.
adc_base.ADCMuxP = ADCMUXP_VREF1P8DAC;
adc_base.ADCMuxN = ADCMUXN_VSET1P1;
adc_base.ADCPga = ADCPGA_GAIN_SEL;
AD5940_ADCBaseCfgS(&adc_base);
/* Initialize ADC filters ADCRawData-->SINC3-->SINC2+NOTCH */
adc_filter.ADCSinc3Osr = ADCSINC3OSR_4;
adc_filter.ADCSinc2Osr = ADCSINC2OSR_1333;
adc_filter.ADCAvgNum = ADCAVGNUM_2; /* Don't care about it. Average function is only used for DFT */
adc_filter.ADCRate = ADCRATE_800KHZ; /* If ADC clock is 32MHz, then set it to ADCRATE_1P6MHZ. Default is 16MHz, use ADCRATE_800KHZ. */
adc_filter.BpNotch = bTRUE; /* SINC2+Notch is one block, when bypass notch filter, we can get fresh data from SINC2 filter. */
adc_filter.BpSinc3 = bFALSE; /* We use SINC3 filter. */
adc_filter.Sinc2NotchEnable = bTRUE; /* Enable the SINC2+Notch block. You can also use function AD5940_AFECtrlS */
AD5940_ADCFilterCfgS(&adc_filter);
//AD5940_ADCMuxCfgS(ADCMUXP_AIN0, ADCMUXN_VSET1P1); /* Optionally, you can change ADC MUX with this function */
/* Enable all interrupt at Interrupt Controller 1. So we can check the interrupt flag */
AD5940_INTCCfg(AFEINTC_1, AFEINTSRC_ALLINT, bTRUE);
//AD5940_AFECtrlS(AFECTRL_ADCPWR|AFECTRL_SINC2NOTCH, bTRUE);
//AD5940_AFECtrlS(AFECTRL_ADCCNV, bTRUE);
AD5940_ADCPowerCtrlS(bTRUE);
AD5940_ADCConvtCtrlS(bTRUE);
AD5940_ADCMuxCfgS(adc_pin[3], ADCMUXN_AIN0);
reading();
AD5940_ADCMuxCfgS(adc_pin[2], ADCMUXN_AIN0);
while(1){
//AD5940_ADCMuxCfgS(adc_pin[4], ADCMUXN_AIN0);
Serial.println(getVolt()*1000000);
//delay(500);
//AD5940_ADCMuxCfgS(adc_pin[3], ADCMUXN_AIN0);
//Serial.println(getVolt()*1000000);
//delay(500);
}
}
void setup() {
Serial.begin(115200);
AD5940_config();
AD5940_Main();
}
void loop() {
// put your main code here, to run repeatedly:
}
