Accelerometer output from LSM303DLH carrier board reads "0"

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1

Dear Forum Members,
I am trying to interface LSM303DLH carrier board with MSP430. My problem is when I read the accelerometer, it reads all zero values. My code is able to detect the presence of LSM303 over I2C with address 0x18.

I have attached a part of my code below:

void write_ACC_REG(unsigned char byteCount, unsigned char *field)
{
TI_USCI_I2C_transmitinit(0x18,0x12); // prescaler generates I2C of 100KHz
while( TI_USCI_I2C_notready() ); 
if(TI_USCI_I2C_slave_present(0x18)) // check slave address
	{TI_USCI_I2C_transmit(byteCount,field);} 
}

char read_ACC(unsigned char count1)
{unsigned char val1;
unsigned char store1[1] = {'j'};
TI_USCI_I2C_receiveinit(0x18,0x12); 
while( TI_USCI_I2C_notready() ); 
TI_USCI_I2C_receive(count1,store1);
while( TI_USCI_I2C_notready() ); // wait till bus is free before leaving this function
val1 = store1[0];
return val1;
}

unsigned char initial1_ACC[2] = {LSM303DLH_CTRL_REG1_A, 0x27};
unsigned char initial2_ACC[2] = {LSM303DLH_CTRL_REG4_A, 0x40};
unsigned char reg_DATA_ACC[1] = {(LSM303DLH_OUT_X_L_A | 0x80)};

void main(void){
	unsigned char X_H_A, X_L_A, Y_H_A, Y_L_A, Z_H_A, Z_L_A;
        write_ACC_REG(2,initial1_ACC); // enable ACC 
	write_ACC_REG(2,initial2_ACC); // REG4_A
	
	for (;;){
	write_ACC_REG(1,reg_DATA_ACC);
	_delay_cycles(200000);
	X_L_A = read_ACC(1);
	X_H_A = read_ACC(1);
	Y_L_A = read_ACC(1);
	Y_H_A = read_ACC(1);
	Z_L_A = read_ACC(1);
	Z_H_A = read_ACC(1);

	send2pc(X_L_A); // this function transmits data over RS232 link to PC
	_delay_cycles(1000);
	send2pc(X_H_A);
	_delay_cycles(1000);
	send2pc(Y_L_A);
	_delay_cycles(1000);
	send2pc(Y_H_A);
	_delay_cycles(1000);
	send2pc(Z_L_A);
	_delay_cycles(1000);
	send2pc(Z_H_A);
	_delay_cycles(1000);
}

Can anyone please tell me where am I going wrong? Am I missing something?
I will highly appreciate any help to resolve this problem.

Regards,
Nick

2

I also tried to reduce length of cable from board to the controller, but didn;t help.

A quick summary of my code is:

  1. Use 0x18 as I2C address for accelerometer
  2. Write 0x27 to REG1 --> Before writing code checks if the slave is present or not
  3. Write 0x40 to REG4
  4. Write 0xA8 to OUT_X_L_A --> Wait for 20000 for the data to get updated. CLK of CPU is 1MHz and that of I2C is 100KHz
  5. Read X_L_A, X_H_A, Y_L_A, Y_H_A, Z_L_A, Z_H_A
  6. Send the acquired data to PC over RS232 link

Can someone please point out what I am doing wrong? Or where shall I look for potential problems? Am i missing something?

Will be very grateful to you for your assistance.

Regards,
Nick

3

Hello, Nick.

Could you tell us more about your setup? Is there anything else connected to the MSP430? Could you post a photo of your entire setup, including all the connections?

Also, do you have an Arduino that you can use to try the example programs?

- Jeremy

4

Hi Jeremy,

Thank you for your response! I will take a pic of my setup and put it up here.

But do you think I am missing any step in the reading accelerometer. There is nothing else connected to I2C line only the LSM303DLH carrier board.

Unfortunately, I do not have Adruino and so I could not try out sample example. What do you suspect might be going wrong? Any one any pointers.

Regards,
Nick

5

I am not sure. Could you try reading the WHO_AM_I address and see if you get the correct value? Also, could you try communicating with the magnetometer and see if you can get any readings?

- Jeremy

6

Hi Nick,

short question, why are you writing to the OUT_X_L register?
You should only read from this register, right?