xadow with pic

[vish287]

I am using the xadow multichannel gas sensor with pic microcontroller using FPC DIP addapter using 0.5mm FPC. I have converted this ardiuno code.

I communicate with it using software I2C and using address 0x04 for device address. I have certain queries . please guide me.

1) when I use device ID 0x04, I use 0x08 for write and 0x09 for read I get LED D1 on when I send command 0x21 for power on as i2c_xadow_start(); i2c_xadow_sendbyte(0x08); // device address i2c_xadow_sendbyte(0x21); // to start the sensor heater i2c_xadow_stop(); delay_ms(10);

2) now when I change device address using command 0x23

so Device Id 0x04 to 0x10 Write command 0x20 and read 0x21

power on is working I again change the Device ID to 0x04 so communication to device is working... 3) now as provided by your ardiuno code, when I write code to simple read the 0x11 resister for res0[0], I should get buffer[0] to buffer[3] values. I have taken buffer[4] as unsigned char but I am getting 0xFF (255)

my code for read data is as under

long readData(unsigned char addr) // int { //int timeout = 0; unsigned char buffer[4]; long checksum = 0;// int? // unsigned char? long rtnData = 0; //int?

i2c_xadow_start();
i2c_xadow_sendbyte(0x08); // default device address
i2c_xadow_sendbyte(addr);  // give the address which is to be read
delay_ms(50); // change delay if needed
i2c_xadow_start();
i2c_xadow_sendbyte(0x09); // read the device

delay_ms(50); buffer[0] = i2c_xadow_readbyte(0); // read the four bytes buffer[1] = i2c_xadow_readbyte(0); delay_ms(50); buffer[2] = i2c_xadow_readbyte(0); buffer[3] = i2c_xadow_readbyte(1); i2c_xadow_stop(); delay_ms(50); checksum = (long)(buffer[0]+buffer[1]+buffer[2]); // if(checksum != buffer[3]) // { // return -4; // // // // } // else // { rtnData = ((buffer[1] << 8) + buffer[2]); // } return (rtnData);//successful }

please guide me why I am not getting values for read operation.

[KillingJacky]

Hi, I think you should check your implementation of i2c_xadow_readbyte function, or even all the soft i2c related functions. I noticed that you might mix up the i2c device address and the register address inside a i2c device. Additionally, the default i2c address of this sensor 0x04 is a 7 bits i2c address. 7 bits i2c address has no sense of the increase between read and write.

[vish287]

yes sir. I have checked this functions with other sensor BMP180 and it is giving me all the parameters with this soft I2C. now as it is 7 bit address as 0x04 so using write it will be 0x08 and for read 0x09. as I2C protocol, I am sending device address, then register address and device address with read as 0x09.

Here for trial base i have take delays of 50msec. in your ardiuno code you have just taken delay_(2). Now "7 bits i2c address has no sense of the increase between read and write." how it will work here? here with I am attaching my .c file please guide me either it is data type issue or any other. thanking you. code.docx

[KillingJacky]

Hi vish,

Looking into the arduino code

int16_t MutichannelGasSensor::readData(uint8_t cmd)
{
    uint16_t timeout = 0;
    uint8_t buffer[4];
    uint8_t checksum = 0;
    int16_t rtnData = 0;

    //send command
    sendI2C(cmd);
    //wait for a while
    delay(2);
    //get response
    Wire.requestFrom(i2cAddress, (uint8_t)4);    // request 4 bytes from slave device
    while(Wire.available() == 0)
    ......

void MutichannelGasSensor::sendI2C(unsigned char dta)
{
    Wire.beginTransmission(i2cAddress);               // transmit to device #4
    Wire.write(dta);                                    // sends one byte
    Wire.endTransmission();                             // stop transmitting
}

There's a STOP between address writing transmission and the following reading transmission. So I guess you should issue a STOP here:

The simulated I2C slave might not support repeated START operation. Please give a try with the above workout and feedback with any result.

Thank you.

[vish287]

Hi, I want to know in the code how the ratio range is decided? as from data sheet its difficult to get the exact ration range of RS/R0 for calculations. Thanks

[KillingJacky]

Hi, The ratio is decided from the curve in the datasheet, there's no exact formula but we simulated one with sample points extracted from the curve.