Interfacing AD8495 K-Type Thermocouple Amplifier with Arduino

Overview
In this tutorial we will be interfacing
AD8495 Analog Output K-Type Thermocouple Amplifier
with
Arduino
microcontroller board. Earlier we used
MAX6675
Thermocouple Amplifier with Arduino which is an SPI module. The AD8495 is an
analog output
thermocouple amplifier.
A
thermocouple
is a rugged, low cost
temperature transducer
consisting two dissimilar metals. Its output is proportional to the temperature difference between a
measurement junction
and a
reference junction
. It has a very wide temperature range. Its l
ow level output
(typically tens of microvolts per °C) requires amplification.
The AD8495 thermocouple amplifiers provide a simple,
low cost solution
for measuring thermocouple temperatures. This hookup guide will help you to connect
AD8495 K-Type Thermocouple Amplifier
with
Arduino
UNO Board. Then using the analog output formula, we can write an
Arduino code
to read the detected temperature. Furthermore, we can add a
0.96″ I2C OLED Display
to show the temperature reading on OLED Screen.
Bill of Materials
We need the following components for this tutorial. You can purchase all the components from the given links.
S.N.
Components
Quantity
Purchase Link

Arduino UNO Board

Amazon
AliExpress
SunFounder

AD8495 K-Type Thermocouple Amplifier

Amazon
AliExpress

0.96" SSD1306 I2C OLED Display

Amazon
AliExpress
SunFounder

Jumper Wires

Amazon
AliExpress
SunFounder

Breadboard

Amazon
AliExpress
SunFounder
AD8495 K-Type Thermocouple Amplifier
The
AD8495 K-Type Thermocouple Amplifier
, developed by
Analog Devices
, is particularly suited for applications requiring high precision. As part of the
AD8494/AD8495/AD8496/AD8497
family, it integrates
precision instrumentation amplifiers
with a cold junction compensator to directly produce a
5 mV/°C
output from a K-type thermocouple signal.
This device simplifies the process of temperature measurement by combining an
ice point
reference
with a precalibrated amplifier. This facilitates its use either as a
standalone thermometer
or as part of a switched output setpoint controller. Specifically calibrated for K-type (
chromel-alumel
) thermocouples through laser wafer trimming, the AD8495 ensures high accuracy across its optimized ambient temperature range. It supports a wide variety of supply voltages, from
3 V
for direct interfacing with low-supply ADCs to up to
36 V
for industrial systems requiring broad common-mode input ranges.
The
temperature readings
can be easily obtained by measuring the
output voltage
and applying the equation:
Temperature = (Vout – 1.25) / 0.005 V
For instance, a voltage reading of
1.5VDC
translates to a temperature of
50°C
. The device’s design minimizes self-heating with a total supply current of
180 μA
when unloaded, although it is capable of delivering over
±5 mA
to a load. This amplifier comes with a fully assembled PCB, which includes the
AD8495
and a
TLVH431
1.25V precision voltage reference, a 2-pin terminal block for easy connection to a thermocouple, and a pin header for breadboard integration. Refer to the
AD8495 Datasheet
for more information.
AD8495 Features & Specifications
Works with any K-type thermocouple
Will not work with any other kind of thermocouple other than K type.
Easy to use analog output.
Temp range with 5V power:
-250°C to +750°C output
(0 to 5VDC)
Temp range with 3.3V power:
-250°C to +410°C output
(0 to 3.3VDC)
Sensing Accuracy Range: ± 1°C around room temperature, ± 2°C for −25°C to +400°C
Sensing Temperature Max: 400°C
Sensing Temperature Min: -25°C
Supply Voltage: 3-18V DC
AD8495 Block Diagram & Internal Circuitry
The following image shows a block diagram of the AD8495 circuitry. The AD849x consists of a low offset, fixed-gain instrumentation amplifier, and a temperature sensor.
The AD849x output is a voltage that is proportional to the temperature at the measurement junction of the thermocouple (T
MJ
). A thermocouple signal is so small that considerable gain is required before it can be sampled properly by most ADCs. The AD849x has an instrumentation amplifier with a fixed gain that generates an output voltage of 5 mV/°C for J-type and K-type thermocouples.
T
MJ
= (V
OUT
− V
REF
)/(5 mV/°C)
The AD8495 also includes a temperature sensor for cold junction compensation. This temperature sensor is used to measure the reference junction temperature of the thermocouple and to cancel its effect. An ideal AD8495 achieves this output with an error of less than ±2°C.
Adafruit AD4895 Breakout Board Schematic
AD8495 Breakout Board Pinout
Power & Output Pins
V+
– This is the power pin. This board works with 3.3V and 5V power.
GND
– Common ground pins
OUT
– This is the output voltage pin. Read using an analog input.
Thermocouple Terminal
Red-
– Connect the red or – wire on your thermocouple to this side of the screw terminal.
Ylw+
– Connect the yellow or + wire on your thermocouple to this side of the screw terminal.
Interfacing AD8495 Analog K-Type Thermocouple Amplifier with Arduino
Now let us interface the AD8495 Analog K-Type Thermocouple Amplifier with Arduino. The connection is fairly simple.
Connect the
VCC
of the AD8495 to the
5V
on the Arduino.
Connect the
GND
of the AD8495 to a
GND
pin on the Arduino.
Finally, connect the
Vout (output)
of the AD8495 to one of the Arduino’s analog input pins (e.g.,
A0
)
You may use a breadboard to fit the AD8495 Module. Properly install the thermocouple on the thermocouple terminal of AD8495.
Source Code/Program for Reading the Temperature Value
Here is an Arduino code for interfacing AD8495 Analog Output K-Type Thermocouple Amplifier with Arduino.
This code performs the following actions:
Reads a
temperature value
from a
thermocouple
connected to an Arduino’s analog input pin, converting the raw
analog-to-digital converter (ADC)
value to a voltage.
Calculates the temperature in
Celsius
from the voltage using the characteristics of an AD8495 thermocouple amplifier (
5mV
per degree Celsius with a
1.25V
offset at
0°C
).
Outputs the
measured temperature
to the Serial Monitor every 500 milliseconds.

// Define the ADC pin to which the thermocouple output is connected.
#define THERMOCOUPLE_PIN A0
// Define the analog reference voltage (AREF). This should match your board's voltage, typically 3.3V or 5.0V.
#define ANALOG_REFERENCE_VOLTAGE 5.0
// Define the ADC resolution in bits. For many Arduino models, the default resolution is 10 bits.
#define ADC_BIT_RESOLUTION 10
// Variables to store the raw ADC reading, the calculated voltage, and the calculated temperature.
float
rawAdcReading
calculatedVoltage
measuredTemperature
;
// Function to convert a raw ADC reading to voltage.
// The function takes the raw ADC value as an input and returns the corresponding voltage.
float
convertRawAdcToVoltage
(
int
rawAdcValue
)
{
// The ADC value is converted to voltage by multiplying with the voltage step size.
// The step size is determined by the analog reference voltage and the ADC resolution.
return
rawAdcValue *
(
ANALOG_REFERENCE_VOLTAGE
/
(
pow
(

ADC_BIT_RESOLUTION
)

)
)
;
}
// Function to calculate the temperature in Celsius from the thermocouple voltage.
// The function takes the measured voltage as input and returns the temperature in Celsius.
float
calculateTemperatureFromVoltage
(
float
voltage
)
{
// The AD8495 outputs 5mV per degree Celsius with a 1.25V offset at 0°C.
// To find the temperature, subtract the offset and divide by the voltage per degree Celsius.
return
(
voltage
1.25
)
/
0.005
;
}
void
setup
(
)
{
// Initialize serial communication at 9600 bits per second.
Serial
begin
(
9600
)
;
}
void
loop
(
)
{
// Read the raw ADC value from the thermocouple pin.
rawAdcReading
=
analogRead
(
THERMOCOUPLE_PIN
)
;
// Convert the raw ADC reading to v