In this tutorial ,
we will learn to build a 4 channel opamp amplifier for LM35 from scratch using Kicad.
The original article LM35 4 channel Signal conditioner can be found here
Board can amplify signals from 4 LM35 temp sensors at the same time and can also be used as a general purpose amplifier board that you can use to interface with other analog sensors.
The board is designed to work with both 5V (Arduino,ATmega series,PIC16F) and 3.3V (MSP430) tolerant microcontrollers
The whole process is available in the form of Video from our Youtube channel.
Basic Block Diagram
The Board has 4 LM35 temperature sensors whose outputs are fed into an LM324 quad opamp.
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 maximum temperature voltage of the LM35 is around 3V.
This section allows the sensor to be interfaced with 3V logic level Microcontrollers like STM32 or MSP430.
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 Opamp Amplifier design
LM35 chip generates 10mV for ever 1 degree Celsius rise ,so for a room temperature of 28 degree C ,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.
The opamp is configured in Non Inverting mode with a gain of 3.7.
Below is a small table of Temperature and corresponding voltage values for gain =3.7 showing the range .
Schematics and PCB design
The circuit and PCB is designed using open source EDA Kicad 6.0.
The accompanying video in our website will teach you How to design the LM35 amplifier circuit board (Schematic capture to PCB design )from scratch using Kicad 6.0
Screenshots and 3D renderings an be seen below.
The manufactured PCB for the LM35 temp sensor