Hello. I am using the AD7150 (here datasheet) to get the capacitance values of a parallel plate capacitor sensor that consists of 2 capacitors. I am using both channels, each one for each parallel plate capacitor.
The datasheet has the formula to convert the digital value into capacitance:
C(pf)=(data-12288)*Input_range/40944 ; where I am using 4pf as Input_range.
After getting access to the registers, the capacitance values make no sense, and I am not sure if I did something wrong when accessing the registers o when using the different type of variables (float, int, unsigned int...etc).
The serial monitor shows me (see picture attached) that for a digital value of 23708 I get 1.00 pF, but for a value of 30875 I get 0.00pF, which does not makes sense. When I do the math with a calculator I get 1.11pF and 1.81pF respectively. Plus I couldn´t get the computations with at leats 2 decimals, it keeps showing ".00".
Hope I am clear enogh. Thanks in advance. I am attaching the code,
#include <Wire.h>
int chip_addr = 0x48; //AD7150 adress
#define ch1_dataH_addr 0x01 //Address to point the Data High of Ch1
#define ch1_dataL_addr 0x02 //Address to point the Data Low of Ch1
#define ch2_dataH_addr 0x03 //Address to point the Data High of Ch2
#define ch2_dataL_addr 0x04 //Address to point the Data Low of Ch2
#define ch1_SetupR_addr 0x0B //Setup (range) register address for Ch1
#define ch2_SetupR_addr 0x0E //Setup (range) register address for Ch2
#define ConfigR_addr 0x0F //Configuration register (operation mode -threshold-)
#define Ch1_ThHR_addr 0x09 //Ch1 Threshold High Register
#define Ch1_ThLR_addr 0x0A //Ch1 Threshold Low Register
#define Ch2_ThHR_addr 0x0C //Ch2 Threshold High Register
#define Ch2_ThLR_addr 0x0D //Ch2 Threshold Low Register
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
Wire.begin();
}
void rconfig1()
{
Wire.beginTransmission(chip_addr);
Wire.write(ch1_SetupR_addr); //Move pointer to the register address
Wire.write(203); //Setup features for range (bx11001011)
Wire.endTransmission();
}
void rconfig2()
{
Wire.beginTransmission(chip_addr);
Wire.write(ch2_SetupR_addr); //Move pointer to the register address
Wire.write(203); //Setup features for range (bx11001011)
Wire.endTransmission();
}
void rconfig3()
{
Wire.beginTransmission(chip_addr);
Wire.write(ConfigR_addr); //Move pointer to the register address
Wire.write(185); //Configuration of the threshold mode bx10111001
Wire.endTransmission();
}
void loop() {
//Get capacitance data
// move the register pointer back to the second register
Wire.beginTransmission(chip_addr); // "Hey, AD7150 @ 0x48! Message for you"
Wire.write(1); // "move your register pointer back to 01h"
Wire.endTransmission(); // "Thanks, goodbye..."
// now get the data from the AD7150
Wire.requestFrom(chip_addr, 4); // "Hey, CN75 @ 0x48 - please send me the contents of your first two registers"
while(Wire.available()) // slave may send less than requested
{
byte ch1H = Wire.read(); // first received byte stored here
byte ch1L = Wire.read(); // second received byte stored here
byte ch2H = Wire.read(); // third received byte stored here
byte ch2L = Wire.read(); // fourth received byte stored here
unsigned int ch1 = ch1H*256 + ch1L; //Concatanates the two bytes into one 16 bit word for capacitor 1.
unsigned int ch2 = ch1H*256 + ch1L; //Concatanates the two bytes into one 16 bit word for capacitor 2.
float Cap1 = (ch1-12288)*4/40944; // Converts the digital value into capacitance, formula from datasheet.
float Cap2 = (ch2-12288)*4/40944;
//print the data on serial monitor, data that was gotten from the registers that store capacitance values
Serial.print("Ch1=");
Serial.print(ch1, BIN);
Serial.print(" Ch1=");
Serial.print(ch1);
Serial.print(" C1=");
Serial.print(Cap1,2);
Serial.print(" Ch2=");
Serial.print(ch2, BIN);
Serial.print(" Ch2=");
Serial.print(ch2);
Serial.print(" C2=");
Serial.println(Cap2,2);
}
delay(700);
}
