EP-0031

Raspberry Pi LM75B Temperature Sensor v1.0 SKU:EP-0031

Product Feature

• 9bit high resolution ADC in chip
• Temperature resolution of 0.125°C.
• I2C bus plug and play
• Compatible with all kind of development board.

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Compatibility List

• Compatibility

Platform	LM75B temperature Sensor Version 1.0	Notes
Raspberry Pi 3 Model B Plus	WIP	WIP: work in process
Raspberry Pi zero	√
Raspberry Pi zero W	√
Raspberry Pi 3 Model B	√
Raspberry Pi 2 Model B	√
Raspberry Pi Model B+	√

Port

• Raspberry Pi GPIO pins

px300

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Product Parameters

• Working voltage: 1.8V-5.5V, accuracy can be up to 0.5 when working voltage is higher than 3v.
• Temperatures range from−55°C to +125°C
• Supply current of 3.5µA in shutdown mode for power conservation
• Temperature accuracy of: ±2°C from−25°C to +100°C
• Temperature accuracy of: ±3°C from−55°C to +125°C

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Package Include:

• 1 x Raspberry Pi LM75B Temperature Sensor v1.0

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Typical Application

• Industrial controllers
• Environmental monitoring
• Smart home
• Interactive devices

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How to wire it up

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How to use it

• i2c-tools package is required, so you should install it before you get temperature as following command:
  

sudo apt-get update && sudo apt-get -y install i2c-tools

• Enable I2c function by editing /boot/config.txt,make sure it contain this two parameter as following:
  

device_tree=bcm2710-rpi-3-b.dtb
dtparam=i2c_arm=on

• • Or you can use this command to enable I2C:
    

sudo raspi-config

• • Select as this picture, then you can enable I2C easily.

• Please Remember to reboot your Raspberry Pi.
• After rebooting, please open a terminal and input this command to get temperature:
  

i2cget -y 1 0x48 0x00 w |awk '{printf("%0.1f C\n",(a=((("0x"substr($1,5,2)substr($1,3,1))*0.0625)+0.1) )>128?a-256:a)}'
Result:

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Examples

• Shell scripts:
  

You can create a file called lm75.sh and edit as following:
#!/bin/bash
while true
do
i2cget -y 1 0x48 0x00 w | awk '{printf("%.1f C.\n", (a=((("0x"substr($1,5,2)substr($1,3,1))*0.0625)+0.1) )>128?a-256:a)}'
sleep 1
done
and set an execute right to this file:
chmod +x lm75.sh && bash lm75.sh

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• C code: You can login to your Raspberry Pi and open a terminal, and then download the zip package from this link below:

File:LM75 C.tar.gz.zip
unzip it and compile it.
unzip LM75_C.tar.gz.zip
tar -xf LM75_C.tar.gz
cd LM75_C/
make
./test.o


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• Python running in command line:
  
  • If you want to use python to drive this sensor, you have to install this two packages first.

sudo apt-get update
sudo apt-get install -y python-smbus python-scipy

• • Create a file called LM75.py as below:

import time
import smbus

LM75_ADDRESS		 = 0x48

LM75_TEMP_REGISTER 	 = 0
LM75_CONF_REGISTER 	 = 1
LM75_THYST_REGISTER 	 = 2
LM75_TOS_REGISTER 	 = 3

LM75_CONF_SHUTDOWN  	 = 0
LM75_CONF_OS_COMP_INT 	 = 1
LM75_CONF_OS_POL 	 = 2
LM75_CONF_OS_F_QUE 	 = 3


class LM75(object):
	def __init__(self, mode=LM75_CONF_OS_COMP_INT, address=LM75_ADDRESS, busnum=1):
		self._mode = mode
		self._address = address
		self._bus = smbus.SMBus(busnum)

	def regdata2float (self, regdata):
		return (regdata / 32.0) / 8.0
	def toFah(self, temp):
		return (temp * (9.0/5.0)) + 32.0

	def getTemp(self):
		raw = self._bus.read_word_data(self._address, LM75_TEMP_REGISTER) & 0xFFFF
		raw = ((raw << 8) & 0xFF00) + (raw >> 8)
		return self.toFah(self.regdata2float(raw))

and then create another file called test.py:

import LM75

sensor = LM75.LM75()

print sensor.getTemp()

• • execute by this command:
    

python test.py

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FAQ

• Question: I've tried to measure temperature with LM75B sensor that bought from your store, but why did i get the data that can not approach to the 0.125 resolution ?
  • Answer: Because the accuracy resolution is lower than ADC resolution,so you can not get the exactly temperature.
• Question: why the temperature that i measured is far away from my friend's data?
  • Answer: Because different environment can cause the resolution change, for example, your system is too busy or there is a heat source nearby may cause the resolution have some offsets.

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Reference

http://www.ti.com/product/LM75B

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