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

From 52Pi Wiki
Jump to: navigation, search

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.

Port

  • Raspberry Pi GPIO pins
LM75new3.jpg
px300



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

Package Include:

  • 1 x Raspberry Pi LM75B Temperature Sensor v1.0

Typical Application

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

How to wire it up

Lm75new1.jpg



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

Lm75.png


    • Select as this picture, then you can enable I2C easily.
Lm752.png


  • 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:

Lm753.png



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


  • 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

Lm75c.png



  • 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

Lm75python.png



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.

Reference

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