RE: Write command for HRMI board using TWI

Levi — Tue, 28 Feb 2017 00:02:09 GMT

Hi Jørgen,

Thank you very much for the response. I have corrected my function as you suggested. However, I am still unable to read any heart rate values and it appears the the SDA and SCL lines are not communicating whatsoever. Can you help me with this?

You have answered my original question so I will accept it, and I will go ahead and create a new question in the devzone for future use. New question here.

Thank you very much!

Levi

RE: Write command for HRMI board using TWI

Jørgen Holmefjord — Mon, 27 Feb 2017 14:04:07 GMT

Hi,

From the data sheet is see the following statement:

Commands and arguments are encoded as 8-bit binary values. Command Sequences consist of 1- or 2-byte I2C write sequences (the command byte followed by any required argument byte) followed by the STOP condition.

This is not different from the TWI examples in our SDK. However, your start_HR() function does not look entirely correct.

You set the length parameter of the nrf_drv_twi_tx() function to 3, but you only pass a 1-byte variable to argument p_data. If I understand you correctly, you want to send <0x47><0x03> to get 3 HR values? This can be done like this:

ret_code_t start_HR(uint8_t num_samples) 
{
	ret_code_t ret_code;
	uint8_t reg[2] = {HRMI_GET_HR_DATA, num_samples}; // <0x47>
	ret_code = nrf_drv_twi_tx(&m_twi, HRMI_I2C_ADDR, reg, sizeof(reg), false);
	return ret_code;
}

And then call the function with the number of samples you want:

start_HR(0x03);

Best regards,

Jørgen