6 Channel Temperature Meter

I always wanted a thermal camera for measuring temperature from different locations at the same time. But the thermal camera is expensive for me, so I decided to make a cheap DIY multi-channel temperature meter for scientific use, which has a −40°C to 270°C wide temperature range 

In this project, we are making a temperature meter project that has 6 NTC thermistors and an OLED screen that will show the reading from the different temperature sensors simultaneously. All of this is controlled by Seeed Studio XIAO SAMD21

1* Seeed Studio XIAO SAMD21

1* 0.91in 128x32 OLED screen 

6* 100k NTC thermistor 

6* 4.7k resistors 0805 SMD  (resistor kit 0805)

6* KF301 2 Pin 5.08mm Pitch Plug-in Screw Terminal Block Connector

An NTC thermistor, short for Negative Temperature Coefficient thermistor, is a type of resistor that exhibits a decrease in resistance as temperature increases. This behavior is due to the semiconductor material used in its construction, which allows more electrons to flow when heated. NTC thermistors are commonly employed as temperature sensors due to their high sensitivity and wide operating range. To measure temperature, an electrical current is passed through the thermistor, and the resulting voltage drop is measured. This voltage drop is proportional to the thermistor's resistance, which in turn is inversely proportional to the temperature. For this project, we are using a 100K NTC thermistor which is cheap and widely available. It is used in 3D printers, so it comes with a 1-meter wire.

To measure temperature with an NTC thermistor, we can use a simple voltage divider circuit, with the thermistor as one of the resistors. The output voltage of the bridge is proportional to the resistance of the thermistor, which in turn is inversely proportional to the temperature. We can use a microcontroller to measure these voltages and convert them to temperature. and used a small OLED screen for interfacing that data 

I designed this PCB according to the schematics given above using Easyeda and exported it to a Gerber file for fabrication

Pcb assembly was straightforward. I just used my soldering iron to solder all the components. It was easy to solder the wire terminals, xiao, and OLED. But soldering the small 4.7k SMD resistor was taught so I need to invest in some SMD rework stations, if you need this Gerber file let me know in the comments

you can change the GPIO pins and the value of the pullup resister in this part of the code

const int numThermistors = 6;
const int analogPins[numThermistors] = {A0, A1, A2, A3, A6, A7};
const float pullUpResistance = 4700.0; // 4.7kohm
const float referenceResistance = 100000.0; // 100k ohm at 25°C
const float betaCoefficient = 3950.0; // Beta coefficient for the NTC thermistor
const float nominalTemperature = 30.5; // Nominal temperature for the NTC thermistor in °C

if you are not getting the expected temperature you can play with these values. find the attached .ino file for the full code

now let's test this, all of this PCB is working with the USB power from Xiao, for this test I connected six NTC Thermistors through the screw terminal. you can use a Kapton tape if you need to attach the sensor to a body that needs to be measured

I am not saying that this is an alternative to a thermal camera, but it has some use cases, like monitoring the temperature of different electronic components of a PCB at the same time and monitoring temperature for scientific research. it is only an affordable alternative