Display float data in nRF Connect

Question

Hi. 
 I transmit latitude and longitude data via bluetooth to my smartphone. 
 But in nRF Connect the data are displayed in HEX format (see screenshot), although in the terminal output the latitude and longitude are displayed correctly in float format (for example: 35.120275). 
 
 Please tell me how to display data correctly in nRF Connect. 
 Thank you.

Jørgen Holmefjord · Accepted Answer

This code must certainly generate warnings in your build, does it not? 
 You are trying to pass a char array to a uint32_t parameter. " mybuf" will contain a pointer to the RAM location where the data is stored. In my_lbs_send_latitude_notify(), you have one input variable, which is not a pointer. The value assigned to this parameter will be stored in a new local variable inside the function, not a reference to the external data. When you pass the mybuf variable to this funtion, it will copy the RAM address where the buffer i stored into latitude_value, not the data stored in mybuf. When you try to pass the reference to latitude_value (&latitude_value) to bt_gatt_notify, this will be the address of the local variable. The sizeof function will also just report the size of an uint32_t, not the size of the buffer, since it is not aware that a buffer was passed to the variable. 
 If you print the values, it should look something like this: 
 mybuf=0x20005244
&mybuf=0x20005244
sizeof(mybuf)=8

latitude_value=0x20005244
&latitude_value=0x2000522c
sizeof(latitude_value)=4 
 You should modify the my_lbs_send_latitude_notify() function to take a pointer and buffer length as input, and pass this further to the bt_gatt_notify() function: 
 int my_lbs_send_latitude_notify(uint32_t *latitude_value_string, uint32_t latitude_string_length)
{
	if (!notify_latitude_enabled) {
 return -EACCES;
	}

return bt_gatt_notify(NULL, &my_lbs_svc.attrs[10], latitude_value_string, latitude_string_length);
}

void send_data(void)
{
 float x = 35.120275;
 char mybuf[8] = {0};
 
 gcvt(x, 8, mybuf);
 my_lbs_send_latitude_notify(mybuf, sizeof(mybuf));
} 
 Best regards, Jørgen

Display float data in nRF Connect

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