LAUNCHXL2-570LC43: Unsure of procedure to connect with an INA219 Current Sensor through I2C.

Hi Stefano,

Actually, I2C from master end designed in such way that can be connected to any of the I2C slave device. So, it is difficult to find documentation for all the slave devices. However, in slave datasheet only they should mention the procedure and protocol related to that corresponding device.

This is new I2C slave device for me, however i can help you with it by understanding the device.

Did you connect any pull-up registers over SCL and SDA lines?

I2C will not work without external pull-up resistors.

Make sure to connect external pull-up resistors on SDA and SCL lines. The pullup should neither be too high and nor be too small, preferably in between 2.2K to 4.7K. 

Even you cannot use internal pull-up resistors as well, because the internal pullups are too weak to be used for I2C. They're just strong enough to keep the pins from floating.  You have to provide external pull-up to I2C signals.

So please connect pullup resistors in between i2c lines and 3.3v supply in the board.

For more details you can refer below thread, here also customer initially tried without pullup's and found the communication is not working, and finally he connected external pullup resistors with 2.2K then he found that communication is working.

For more details refer these threads:

(18) TMS570LS3137: Temperature Sensor(tmp101na/3k) - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

(18) TMS570LS1224: Problem of not being able to send value with i2cSend() in I2C - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

(18) TMS570LS3137: I2C is not working - Arm-based microcontrollers forum - Arm-based microcontrollers - TI E2E support forums

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Thanks & regards,
Jagadish.

Hi Jagadish,

My INA219 has internal pull-up resistors attached to the board of about 10KΩ. I'm guessing that is too high and would prevent any I2C communication right?

Thank you very much for your help!

You are correct.

The pullup should neither be too high and nor be too small, preferably in between 2.2K to 4.7K. 

Thank you for letting me know, I am currently using this code to test out if communication works with the INA219. I notice that the voltage on the SCL line drops from 3.3V to 0V when debugging, signaling that communication is happening, but I cannot seem to get past the i2cReceive(...); function since it gets stuck on the "while ((i2c->STR & (uint32)I2C_RX_INT) == 0U) {}" function. Could you provide me with some insights as to why it would be getting stuck there?

#include "HL_sys_common.h"
#include "HL_i2c.h"
#include "HL_sys_core.h"
#include <stdio.h>

#define INA219_ADDR        0x40
#define INA219_REG_BUSVOLT 0x02

int main(void)
{
    uint8 tx_data = INA219_REG_BUSVOLT;
    uint8 rx_data[2];

    i2cInit();

    /** Write register address to INA219 **/
    i2cSetSlaveAdd(i2cREG1, INA219_ADDR);
    i2cSetDirection(i2cREG1, I2C_TRANSMITTER);
    i2cSetCount(i2cREG1, 1);
    i2cSetMode(i2cREG1, I2C_MASTER);
    i2cSetStart(i2cREG1);
    i2cSend(i2cREG1, 1, &tx_data);  
    i2cSetStop(i2cREG1);

    /** Read 2 bytes from bus voltage register **/
    i2cSetDirection(i2cREG1, I2C_RECEIVER);
    i2cSetCount(i2cREG1, 2);
    i2cSetMode(i2cREG1, I2C_MASTER);
    i2cSetStart(i2cREG1);
    i2cReceive(i2cREG1, 2, rx_data);
    i2cSetStop(i2cREG1);

    uint16 raw = ((uint16)rx_data[0] << 8) | rx_data[1];

    // Convert to actual voltage
    float voltage = (raw >> 3) * 0.004;  // 4 mV per bit

    printf("%d", voltage);
}

Hi Stefano,

I verified your code and also the datasheet of the INA219.

1. First i want to make sure this, as you are using slave address as 0x40 that means you should connect A1 and A0 address lines to the ground. I hope you did this in your hardware.

2. Now i made some changes to your code, try with this modified code once and update the status to me:

#include "HL_sys_common.h"
#include "HL_i2c.h"
#include "HL_sys_core.h"
#include <stdio.h>

#define INA219_ADDR        0x40
#define INA219_REG_BUSVOLT 0x02

int main(void)
{
    uint8 tx_data = INA219_REG_BUSVOLT;
    uint8 rx_data[2];

    i2cInit();

    /** Write register address to INA219 **/
    i2cSetSlaveAdd(i2cREG1, INA219_ADDR);
    i2cSetDirection(i2cREG1, I2C_TRANSMITTER);
    i2cSetCount(i2cREG1, 1);
    i2cSetMode(i2cREG1, I2C_MASTER);  
    i2cSetStop(i2cREG1);
    i2cSetStart(i2cREG1);
    i2cSend(i2cREG1, 1, &tx_data);
	
	/* Wait until Bus Busy is cleared */
    while(i2cIsBusBusy(i2cREG1) == true);

    /* Wait until Stop is detected */
    while(i2cIsStopDetected(i2cREG1) == 0);
	
	/* Clear the Stop condition */
    i2cClearSCD(i2cREG1);

    /** Read 2 bytes from bus voltage register **/
    i2cSetDirection(i2cREG1, I2C_RECEIVER);
    i2cSetCount(i2cREG1, 2);
    i2cSetMode(i2cREG1, I2C_MASTER);
    i2cSetStop(i2cREG1);
    i2cSetStart(i2cREG1);
    i2cReceive(i2cREG1, 2, rx_data);

    uint16 raw = ((uint16)rx_data[0] << 8) | rx_data[1];

    // Convert to actual voltage
    float voltage = (raw >> 3) * 0.004;  // 4 mV per bit

    printf("%d", voltage);
}

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Thanks & regards,
Jagadish.