Introduction: Building a 4 Channel LM35 Temperature Sensor Amplifier for Arduino/MSP430 Microcontroller

By xanthium enterprises

We will learn to design and build an 4 channel LM35 temperature sensor signal conditioner amplifier circuit based on the popular opamp LM324 using Kicad 6.0.

This is a free YouTube course ,where we learn to build a opamp amplifier for temperature sensors from scratch from conception ,design, schematic capture to PCB design.

The board can be used to monitor temperature from 4 different sources at the same time and can be used for building your own data acquisition system using Arduino (ATmega328P) or MSP430 Microcontroller.


Original tutorial



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Main Features

  1. Board consists of 4 analog channels for connecting the outputs of the LM35 chip
  2. 4 output channels that gives the amplified output of the LM35 chip in the range of 0-5V
  3. Board also has 4 amplified outputs that gives the amplified voltage in the range from 0-3V
  4. Gain of all the channels is 3.7
  5. Board can also be used as a general purpose amplifier board that you can use to interface with other analog Sensors(Thermistors)
  6. Components used in the circuit are through hole components
  7. Learn valuable soldering skills

Supplies

All the components used in the tutorial can be acquired from your friendly neighborhood electronics shop

  1. LM324A Opamp 14 pin DIP
  2. LM35 Temperature Sensor
  3. 100nF Ceramic Disc Capacitor
  4. 10uF/16V Electrolytic Capacitor
  5. 1N5819 Diode
  6. 10K Resistor
  7. 27K Resistor


if you want a premade PCB ,you can get it from our website.


Circuit diagram can be downloaded from our website

Step 1: Intro to LM35 Temperature Sensor IC

  • The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly proportional to the Centigrade temperature scale.
  • The LM35 device is rated to operate over a −55°C to 150°C temperature range,  
  • LM35 device draws only 60 μA from the supply, 
  • LM35 low self-heating of less than 0.1°C in still air.
  • In our case we will use the temperature sensor from 2 to 150 Celsius range only .
  • We will be using a single 5V supply to power the chip.


Step 2: Block Diagram for 4 Channel LM35 Temperature Sensor Amplifier

  • The above image show the basic block diagram of the 4 channel LM35 based temperature sensor board.
  • The Board has 4 LM35 temperature sensors whose outputs are fed into an LM324 quad opamp.
  • The Channels can also be used to amplify other analog signals
  • The opamp amplifies the signal (0-5V range) in such a way that the max temperature voltage of the LM35 is near 5V.This section allows the sensor to be interfaced with 5V logic level Microcontrollers like AVR ATmega328P,Arduino,PIC16F etc.
  • The Output is also given to a potential divider network which scales the voltage in 0-3V range. Here max temperature voltage of the LM35 is around 3V.This section allows the sensor to be interfaced with 3V logic level Microcontrollers like MSP430.

Step 3: Circuit Diagram

Step 4: LM324 Opamp Amplifier Design for LM35

LM35 chip generates 10mV for ever 1 degree Celsius rise ,so for a room temperature of 28oC ,the chip will generate 280mV or 0.28V

Low voltage signals like this are prone to interference from noise sources which may corrupt the signal.

LM324 has 4 internal amplifiers. Here i will only be showing one of the amplifiers.

The opamp is configured in Non Inverting mode with a gain of 3.7.

Gain(Av) = 1+Rf/R

Here Rf =27K and R =10K

Main reason gain is chosen as 3.7 is because for

the temperature value of 135 degrees the voltage output of opamp will be 5V. This allows to measure almost the whole range of sensor LM35. 

Step 5: Designing Circuit Schematics of 4 Channel LM35 Temp Sensor Amplifier on Kicad 6.0

Check our Youtube video on how to design the entire circuit using Kicad 6.0 EDA.

The tutorial teaches you

  1. To create schematic in Kicad 6.0
  2. Annotate the schematic components in Kicad 6.0
  3. Assign the schematic components with their respective foot prints in Kicad 6.0

Step 6: Designing PCB for 4 Channel LM35 Temp Sensor Amplifier on Kicad 6.0

Here we learn how to create the PCB for our 4 channel LM35 Amplifier Circuit using Kicad 6.0 and verify it