Measure Temperature from I2C Peripheral Device on NI USB-8452 Controller
This example shows how to communicate with I2C peripheral devices on the NI™ USB-8452 controller. In this example, a TMP102 digital temperature sensor is connected to the NI USB-8452 controller.
The TMP102 is a two-wire serial output digital sensor that can read temperature with a resolution of 0.0625 °C. It can also read temperature values above 128 °C in extended mode.
Set Up Hardware
Connect the SDA, SCL, GND, and VCC pins of the sensor to the corresponding pins on the NI USB-8452 hardware. For this example, connect the SDA and SCL pins of the sensor to Pin 3 and Pin 5 of the NI USB-8452, respectively. Connect the GND and VCC pins to Pin 2 and Pin 7 (DIO(0)), respectively.
Connect to I2C Peripheral Device
Search for NI USB-8452 hardware connected to your machine using
ni845xlist and connect to it in MATLAB® using
list = ni845xlist
list=1×2 table Model SerialNumber _____________ ____________ 1 "NI USB-8452" "01F26E0A"
controller = ni845x(list.SerialNumber)
controller = NI845x with properties: Model: "NI USB-8452" SerialNumber: "01F26E0A" AvailableDigitalPins: ["P0.0" "P0.1" "P0.2" "P0.3" "P0.4" "P0.5" "P0.6" "P0.7"] Show all properties, functions
Configure the DIO(0) pin as output and output a logic high level voltage of 3.3 V to power the temperature sensor.
Scan the NI USB-8452 hardware for available I2C addresses. The temperature sensor is represented by the I2C address
address = scanI2CBus(controller)
address = 1×2 string "0x48" "0x53"
Connect to the I2C peripheral device using the
device function with the I2C address returned by
tempSensor = device(controller,I2CAddress=address(1))
tempSensor = I2CDevice with properties: Protocol: "I2C" I2CAddress: 72 BitRate: 100000 ByteOrder: "little-endian" Show all functions
Read Temperature Value
In normal mode, the sensor returns a temperature value digitized into 12 bits, with 8 bits in MSB and 4 bits in LSB. Each LSB is equal to 0.0625 °C. Read two bytes of data from register address 0 of the sensor as
uint8 data type.
Calculate the temperature in °C by using the
tmp102Temperature helper function. You can find this helper function at the end of this example and attached to this example as a supporting file.
data = readRegister(tempSensor,0,2,"uint8"); temperature = tmp102Temperature(data,12)
temperature = 24.7500
Read Temperature with Higher Measurement Limit
You can measure temperatures above 128 °C by using 13 bits in the TMP102 sensor's extended mode. To do so, write the value
'B060' as a hex value to the configuration register at address 1, as specified in the TMP102 device datasheet.
Read the temperature from register address 0 to get a more precise result. Since the TMP102 sensor's conversion rate defaults to 4 Hz, pause MATLAB for about 0.25 seconds before each reading. Convert the data to °C by using the
tmp102Temperature helper function.
write(tempSensor,0x0,"uint8"); pause(0.25); data = read(tempSensor,2,"uint8"); temperature = tmp102Temperature(data,13)
temperature = 24.7500
Change back to the default configuration, as specified in the TMP102 device datasheet.
When you are finished working with the NI USB-8452, clear the associated
clear tempSensor controller
function T = tmp102Temperature(data,numBits) % tmp102Temperature Convert TMP102 raw temperature register data to temperature in °C % % T = tmp102Temperature(data,numBits) % data is 1x2 row vector of uint8 values in big-endian order % numBits corresponds to the TMP102 temperature mode (12 bits for normal % mode, or 13 bits for extended mode) % TMP102 resolution (°C / count) resolution = 0.0625; % Digital temperature output (counts) numShiftBits = 16-numBits; digitalT = bitshift(typecast(uint8(fliplr(data)),'int16'),-numShiftBits); % Temperature in °C T = double(digitalT) * resolution; end