Hello,
I'm attempting to use the AD7747 to read capacitance from a sensor. For now, I'm just trying to get it to work though. I'm not familiar with I2C at all, this is my first attempt.
I know from using the I2C Scanner that the register is at 0x48. Sadly, the code below, which I got from this forum, keeps returning a capacitance value 8.19pF even when a known capacitor is connected.
Any help is greatly appreciated.
#include <Wire.h> //include the library for i2c communication
int capreadybit = (bitRead(TWDR,0)); //initialize variable readybit to be two wire data register's lsb
void setup()
{
Wire.begin(); //sets up i2c for operation
Serial.begin(9600); // we will monitor this via serial cable
Wire.beginTransmission(0x48);
Wire.write(0xBF);
Wire.write(0x00);
Wire.endTransmission();
delay(4);
Wire.beginTransmission(0x48); // begins write cycle
Wire.write(0x07); //address pointer for cap setup register
Wire.write(0xA0); //b'10100000' found from datasheet page 16
Wire.endTransmission(); //ends write cycle
delay(4); // Wait for data to clock out? I'm not 100% sure why this delay is here (or why it's 4ms)
Wire.beginTransmission(0x48); //begins transmission again
Wire.write(0x09); //address pointer for capacitive channel excitation register
Wire.write(0x0E); //recommended value from datasheet
Wire.endTransmission();
delay(4);
Wire.beginTransmission(0x48);
Wire.write(0x0A); //address pointer for the configuration register
Wire.write(0x21); //b'00100001' for continuous conversion, arbitrary VTF setting, and mid-range capacitive conversion time
Wire.endTransmission();
Wire.beginTransmission(0x48);
Wire.write(0x0B); //CAP DAC A Register address (Positive pin data)
Wire.write(0x80); //b'10111111' for enable Cap DAC A
Wire.endTransmission();
Serial.println("Hello!"); //test to make sure serial connection is working
}
void loop()
{
Wire.beginTransmission(0x0B); //talking to chip
Wire.write(byte(0x00)); //status register address
Wire.endTransmission();
Wire.requestFrom(0x0B,1); //request status register data
int readycap;
readycap=Wire.read();
//if((readycap&0x1)==0){ // ready?
Serial.println("Data Ready");
delay(500);
Wire.beginTransmission(0x48); //arduino asks for data from ad7747
Wire.write(0x01); //set address point to capacitive DAC register 1
Wire.endTransmission(); //pointer is set so now we can read the
Serial.println("Data Incoming");
delay(500);
Wire.requestFrom(0x0B,3); //reads data from cap DAC registers 1-3
//while(Wire.available()){
unsigned char hi,mid,lo; //1 byte numbers
long capacitance; //will be a 3byte number
float pf; //scaled value of capacitance
hi=Wire.read();
mid=Wire.read();
lo=Wire.read();
capacitance=(hi<<16)+(mid<<8)+lo-0x800000;
pf=(float)capacitance*-1/(float)0x800000*8.192f;
Serial.print(pf, DEC); //prints the capacitance data in decimal through serial port
Serial.print(",");
//}
Serial.println();
//}
Serial.println("Loop Done");
Serial.println(" ");
delay(1000);
}
ad7747_CDC.ino (3.19 KB)