I'm working on a project using InvenSense's Motion Driver API to read values from the MPU-6050. As a start I'm trying to get the temperature.
Reading the register documentation there is the following sentence.
The temperature in degrees C for a given register value may be computed as: Temperature in degrees C = (TEMP_OUT Register Value as a signed quantity)/340 + 36.53
In the source code of this API there is the following function
int mpu_get_temperature(long *data, unsigned long *timestamp)
{
unsigned char tmp[2];
short raw;
if (!(st.chip_cfg.sensors))
return -1;
if (i2c_read(st.hw->addr, st.reg->temp, 2, tmp))
return -1;
raw = (tmp[0] << 8) | tmp[1];
if (timestamp)
get_ms(timestamp);
data[0] = (long)((35 + ((raw - (float)st.hw->temp_offset) / st.hw->temp_sens)) * 65536L);
return 0;
}
When I search the internet I usually come across this snippet which seems to work
uint8_t buf[2];
mpu_read_reg(0x41, &buf[0]);
mpu_read_reg(0x42, &buf[1]);
uint16_t raw = (((uint16_t) buf[0]) << 8) | buf[1];
float temperature = raw / 340.0f + 36.53f;
Can somebody please explain the line (long)((35 + ((raw - (float)st.hw->temp_offset) / st.hw->temp_sens)) * 65536L) to me?
Is this some sort of type conversion or am I getting something wrong?
This is actually the same.
.temp_sens = 340, .temp_offset = -521