Simple Temperature Indicator Circuit using a Single Transistor

To make a Simple Temperature Indicator Circuit using a Single Transistor is not so hard like people think.

Furthermore, this article makes understand, how anyone can build this easy circuit using one diode, one transistor and some other small parts.

What is a Temperature Indicator Circuit using a Single Transistor:

Firstly, using one transistor, temperature indicator circuit is easy electronic thing that show temperature change by looking.

Typically, we use a thermistor or another temperature-sensitive component to sense heat and this article helps us build the circuit step by step and provides important formulas for accurate results.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors	R1 and R2 values as per calculations	1 each
	Preset 250Ω	1
Semiconductors	Transistor BC547	1
	Diode 1N4148	1
	LEDs red 20mA 5mm	1

To begin with, semiconductors like transistor and diode are simple parts that change how they work when temperature goes up or down.

Also, their behavior is mostly how voltage pass through them and changes when surrounding temperature change.

Moreover, this circuit use one diode and one transistor in bridge way and both these two parts work together because both react similar to temperature change.

First, use the diode as the reference and the transistor to sense heat and keep the diode in a location where the temperature remains constant.

Also, temperature changes can affect the diodes output and lead to incorrect results and we should connect an LED to the transistors collector.

Next, this LED shows temperature difference with light so we can see how much heat is around transistor.

Then keep the diode at room temperature, place the transistor near the heat source to measure temperature, and compare the transistors base-emitter voltage with the diodes voltage.

LED show this difference with more heat and more light and when transistor get hot its voltage goes up, hence, when temperature pass the set limit transistor start working and LED glow more as heat increase.

Safety:

Keep the transistor below 120°C to prevent permanent damage.

Formula and Calculations:

To find temperature limit we need to calculate resistor values using these formula:

R1 = (Ub − 0.6) / 0.005

R2 = (Ub − 1.5) / 0.015

here,

• Ub is the power supply voltage
• 0.6 is the forward voltage drop of transistor BJT
• 0.005 is the normal current for transistor
• 1.5 is the forward voltage drop of red LED
• 0.015 is the normal current for LED to blink properly

How to Build:

To build a Simple Temperature Indicator Circuit using a Single Transistor follow the below mentioned connections steps:

• First, collect all parts needed.
• Next, place the transistor, diode and LED on the breadboard and make sure we connect the transistor the correct way.
• Then, join transistor and diode like bridge connection, because diode is for reference and transistor is for sensing heat.
• After that, connect transistors collector pin to LED and this LED will show heat change by light.
• And to make reference voltage connect diode and keep diode in place where temperature stay same.
• Now connect circuit to preset and this help adjust reference voltage.
• Also, be sure transistor does not get hotter than 120°C or it can break.
• Lastly, if needed we can change circuit to control outside device when temperature changes.

Testing:

• Switch ON the circuit and look at LED, so when temperature goes above the set limit LED will glow more bright to show the heat level.

Conclusion:

To conclude, by following these above steps anyone can make an easy and useful Simple Temperature Indicator Circuit using a Single Transistor and one diode.

Moreover, do not forget to follow safety warnings and also think about changing things if needed to make circuit work better as explained in this article.