I2CADCforPi

I2CAnalogRead.ino

#include <Wire.h>

/*
 * Set I2C Slave address
*/

#define I2C_SLAVE_ADDRESS 0x7
#define SENSOR A0

 
// Measurement 
#define MAX_TICK 50
unsigned int tick = 0;

//Smoothing Factor
#define LPF_FACTOR 0.5

unsigned long lastReadout = 0;

// Variables for the pressure sensor
int _delay = 100;
float Va = 5;
int readSensor = 0;
float Vs = 0;
float pressure = 0;
float pressure_bar = 0;

// I2C Stuff
volatile uint8_t i2c_regs[] =
{
    0, //older 8
    0,
    0,
    0 //younger 8
};

volatile byte reg_position = 0;
const byte reg_size = sizeof(i2c_regs);
volatile unsigned long pressureSmooth;

void requestEvent()
{  

  Wire.write(i2c_regs[reg_position]);

  reg_position++;
  if (reg_position >= reg_size)
  {
      reg_position = 0;
  }

}
 

void setup() {
  /*
   * Setup I2C
   */
  Wire.begin(I2C_SLAVE_ADDRESS);
  Wire.onRequest(requestEvent);

}

int smooth(int data, float filterVal, long smoothedVal){

  if (filterVal > 1){      // check to make sure params are within range
    filterVal = .99;
  }
  else if (filterVal <= 0){
    filterVal = 0;
  }

  smoothedVal = (data * (1 - filterVal)) + (smoothedVal  *  filterVal);

  return (int)smoothedVal;
}

void loop() {

  unsigned long currentMillis = millis();

  /*
   * On tick value 0, do measurements
   */

  if (abs(currentMillis - lastReadout) > MAX_TICK) {

    // Read the values
    int sensorReading = analogRead(SENSOR);

    // Treat them
    Vs = ((float) sensorReading  + 0.5 ) / 1024.0 * 5.0;
    pressure = (Vs*687.8/Va - 18.77)*100; // in DPa

    // Smooth it
    pressureSmooth = smooth(pressure, LPF_FACTOR, pressureSmooth); // in Pa

    // Put the smoothed vaue into the I2C register
    i2c_regs[0] = pressureSmooth >> 24 & 0xFF;
    i2c_regs[1] = pressureSmooth >> 16 & 0xFF;
    i2c_regs[2] = pressureSmooth >> 8 & 0xFF;
    i2c_regs[3] = pressureSmooth & 0xFF;

    // Update the last readout
    lastReadout = currentMillis;
  }
}

piReadI2C.py

import smbus
import time

bus = smbus.SMBus(1) # Indicates /dev/i2c-1
address = 0x7
packet_size = 4

def ReadSensor(_address):
  
  i = 0
  _value = 0
  
  while (i < packet_size):

    _measure = bus.read_i2c_block_data(_address, 0, 1)
    #~ print "Measure"
    #~ print _measure
    
    _value |= _measure[0] << (8*(packet_size-(1+i)))
    i+=1
    
  return _value

while True:
    result = ReadSensor(address)
    #~ print "Result"
    print result
    time.sleep(1)