D_Heidner:
I re-read the spec sheet for the amplifier - I see what you’re doing - but I think you’d still run into a speed problem. I presume you’d be using the sending values to the D/A to adjust for the offset for the bridge during the initial setup. You may want to simply try to see how fast you can read the basic setup with an ordinary Arduino Uno… without the wifi and you can get the speed you want - then try the wifi. Or you may consider a couple of Uno’s with the EPS32 assembling one packet that has the 32 readings in it and sending it out using a MQTT library.
Thank you kindly for the reply Heidner. I have respeced my design. Instead of having 32 channels at once. I divided acquisition into blocks. Each block acquires 8 channels of strain with the help of the XR18910 amplifier. It is similiar to the XR10910( but the XR18910 has 8 channels instead of 16). I have tried using the ADC of the ESP32 but it seems to be very slow. Sampling 8 channels at about 80 samples per second. So i replaced it with the Teensy 3.6, and i am getting about 3000 Samples for 8 channels. which is more than my requirement of 1000Samples/Sec. Although i am having difficulties with controlling the DAC. As controlling the DAC of 1 channel seems to affect the other channels as well. I have attached the code below. It’s quite a simple control. Also i find that i get a lot of noise at the input. Do you have advice for controlling noise for analog circuits?
The below code shows the control of 6 channels. As i am testing with 6 strain gauges at the moment. I am trying to also figure out a way to have the data which is in serial to be sent to a webserver. Preferably via arduino uno? is it possible to that another arduino device like the arduino Yun can receive serial data and transmit this information over wifi to a web server?
#include <Adafruit_MAX31865.h>
#include <TimeLib.h>
#include <TimeLib.h>
#include <WProgram.h>
//#include <Wire.h>
#include <i2c_t3.h>
#include <Filters.h>
Adafruit_MAX31865 max = Adafruit_MAX31865(10, 11, 12, 13); //Temperature
#define RREF 430.0 //Temperature
const unsigned long fiveSeconds = 5 * 1000UL; // Counter for 5 seconds
static unsigned long lastSampleTime = 0 - fiveSeconds; // initialize such that a reading is due the first time through loop()
int StrainInput1 = A0;
float strainValue1 = 0; // variable to store the value coming from the sensor
float strainValue2 = 0;
float strainValue3 = 0;
float strainValue4 = 0;
float strainValue5 = 0;
float strainValue6 = 0;
//float strainValue7 = 0;
//float strainValue8 = 0;
float tempPT100 = 0;
float filterFrequency = 1000.0; //filters out changes faster than 1000Hz
FilterOnePole lowpassFilter( LOWPASS, filterFrequency );
float vd=3.345;
int res=8192;
String sensorOutput;
void strainOutput();
void strainOffset();
void strainGain();
void setup() {
analogReadResolution(13);
Wire.begin(I2C_MASTER, 0x00, I2C_PINS_18_19, I2C_PULLUP_EXT, 400000);
Wire.setClock(400000L); // Set i2C speed to 400Khz
Serial.begin(2000000); // open the serial port at 115200 bps
Serial.println("CLEARDATA");
Serial.println("LABEL,Current time,Strain 1,Strain 2,Strain 3,Strain 4,Strain 5,Strain 6");
Wire.beginTransmission(0x66);
Wire.write(0x07); // LDO register
Wire.write(0x01); // 2.65V
Wire.endTransmission();
strainGain();
max.begin(MAX31865_4WIRE); // set to 2WIRE or 4WIRE as necessary
strainOffset();
}
void loop() {
Wire.beginTransmission(0x66);
Wire.send(0x10); // Call Channel 1
Wire.endTransmission();
strainValue1 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue1 = analogRead(StrainInput1);
Wire.beginTransmission(0x66);
Wire.send(0x12); // Call Channel 2
Wire.endTransmission();
strainValue2 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue2 = analogRead(StrainInput1);
Wire.beginTransmission(0x66);
Wire.send(0x14); // Call Channel 3
Wire.endTransmission();
strainValue3 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue3 = analogRead(StrainInput1);
Wire.beginTransmission(0x66);
Wire.send(0x15); // Call Channel 4
Wire.endTransmission();
strainValue4 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue4 = analogRead(StrainInput1);
Wire.beginTransmission(0x66);
Wire.send(0x18); // Call Channel 5
Wire.endTransmission();
strainValue5 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue5 = analogRead(StrainInput1);
Wire.beginTransmission(0x66);
Wire.send(0x1A); // Call Channel 6
Wire.endTransmission();
strainValue6 = lowpassFilter.input( analogRead( StrainInput1) );
//strainValue6 = analogRead(StrainInput1);
// Wire.beginTransmission(0x66);
// Wire.send(0x1C); // Call Channel 6
// Wire.endTransmission();
// strainValue7 = analogRead(StrainInput1);
//
// Wire.beginTransmission(0x66);
// Wire.send(0x1E); // Call Channel 6
// Wire.endTransmission();
// strainValue8 = analogRead(StrainInput1);
//
unsigned long now = millis();
// if (now - lastSampleTime >= fiveSeconds)
// {
// lastSampleTime += fiveSeconds;
// temperatureCal();
//
// }
resToVolt();
strainOutput();
}
void resToVolt()
{
strainValue1 = strainValue1/res*vd; //Stable readings at 2.42V
strainValue2 = strainValue2/res*vd; //Stable readings at 2.28V
strainValue3 = strainValue3/res*vd; //Stable readings at 2.31V
strainValue4 = strainValue4/res*vd; //Stable readings at 2.84V
strainValue5 = strainValue5/res*vd; //Stable readings at 2.63V
strainValue6 = strainValue6/res*vd; //Stable readings at 2.79V
// strainValue7 = strainValue7/res*vd; //Stable readings at 2.79V
// strainValue8 = strainValue8/res*vd; //Stable readings at 2.79V
}
void strainOutput()
{
sensorOutput ="";
//sensorOutput +="DATA,TIME,";
sensorOutput +=strainValue1;
sensorOutput +=',';
sensorOutput +=strainValue2;
sensorOutput +=',';
sensorOutput +=strainValue3;
sensorOutput +=',';
sensorOutput +=strainValue4;
sensorOutput +=',';
sensorOutput +=strainValue5;
sensorOutput +=',';
sensorOutput +=strainValue6;
//sensorOutput +=',';
// sensorOutput +=strainValue7;
// sensorOutput +=',';
// sensorOutput +=strainValue8;
// sensorOutput +=',';
//sensorOutput +=tempPT100;
Serial.println(sensorOutput);
}
void strainGain()
{
Wire.beginTransmission(0x66);
Wire.send(0x06); // Gain Select
//Wire.send(0x00); // Gain Choice 2
Wire.send(0x04); // Gain Choice 150
Wire.endTransmission();
}
void strainOffset()
{
Wire.beginTransmission(0x66);
Wire.send(0x20); // Access Offset correction register Channel 1
Wire.send(0x00);
Wire.send(0x00);
Wire.endTransmission();
Wire.beginTransmission(0x66);
Wire.send(0x22); // Access Offset correction register Channel 2
Wire.send(0x00);
Wire.send(0x00);
Wire.endTransmission();
Wire.beginTransmission(0x66);
Wire.send(0x24); // Access Offset correction register Channel 3
Wire.send(0x07);
Wire.send(0xFF);
Wire.endTransmission();
Wire.beginTransmission(0x66);
Wire.send(0x25); // Access Offset correction register Channel 4
Wire.send(0x00);
Wire.send(0x00);
Wire.endTransmission();
Wire.beginTransmission(0x66);
Wire.send(0x28); // Access Offset correction register Channel 5
Wire.send(0x00);
Wire.send(0x00);
Wire.endTransmission();
Wire.beginTransmission(0x66);
Wire.send(0x2A); // Access Offset correction register Channel 6
Wire.send(0x00);
Wire.send(0x00);
Wire.endTransmission();
}
void temperatureCal()
{
uint16_t rtd = max.readRTD();
//Serial.print("RTD value: "); Serial.println(rtd);
//float ratio = rtd;
//ratio /= 32768;
//Serial.print("Ratio = "); Serial.println(ratio,8);
//Serial.print("Resistance = "); Serial.println(RREF*ratio,8);
//Serial.print("Temperature = "); Serial.println(max.temperature(100, RREF));
tempPT100 = max.temperature(100,RREF);
}
