Temperature Measuring System with LED Indicator
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Introduction
We all have seen different types of temperature measuring systems where temperature value is shown in the display by number format. But in this project, we will build a simple Temperature Measuring System/Device that can measure room temperature levels and indications by the LED. We need to place this device in your room and it starts showing the temperature level in the LED bar. The number of LEDs turn ON or OFF depends on the room temperature increase or decrease. When the temperature will maximum then the maximum LED will turn ON and when the temperature will minimum then the minimum LED will turn Off.
Project Concept
This is a very simple project and very easy to make it. Few components are needed to build this project, the key components are LM35 Temperature Sensor, 10k potentiometer, LM3915 Logarithmic Dot/Bar Display Driver IC, and LEDs. The LM35 is a 3 pin Temperature Sensor IC, its output voltage change according to the temperature change around it. In this project, it is used to measure the temperature and its analog output voltage goes to the LM3915 IC. The 10k potentiometer is used to set a reference voltage. The LM3915 IC is the main chip of this project, which controls the whole system. This IC control 10 LEDs according to the sensor output voltage. These LEDs are used as an indicator, which indicates temperature Level.
Block Diagram of Temperature Measuring System with LED Indicator
Components Required
| Components Name | Quantity |
| LM3915 Logarithmic Dot/Bar Display Driver IC | 1 |
| LM35 Temperature Sensor | 1 |
| 1K ohm Resistor (R1) | 1 |
| 10K ohm Potentiometer (VR1) | 1 |
| Green LED (LED1,2 & 3) | 3 |
| Yellow LED (LED4, 5 & 6) | 3 |
| Red LED (LED7, 8, 9 & 10) | 4 |
| Slide Switch | 2 |
| 12v Power Supply | 1 |
| PCB board | 1 |
| Connecting Wire | As required in the circuit diagram |
Tools Required
| Tools Name | Quantity |
| Soldering Iron | 1 |
| Soldering wire | 1 |
| Soldering flux | 1 |
| Soldering stand | 1 |
| Multimeter | 1 |
| Desoldering pump | 1 |
| Wirecutter | 1 |
Circuit Diagram of Temperature Measuring System with LED Indicator
Working Principle of Temperature Measuring System with LED Indicator
Once the circuit has been completed, now time to turn on the circuit Power Supply. At the same time, the LM35 Temperature Sensor starts sensing Temperature around it. This is an analog temperature sensor, it can be measure temperature anywhere between -55°C to 150°C. The output voltage of this sensor is directly proportional (Linear) to the temperature around it. Pin 3 is the output pin of this sensor, which output voltage change 10mVolt for every 1°C rise in temperature. This output voltage goes to the Signal Pin (IC Pin 5) of the LM3915 IC.
The LM3915 IC is an Analog Controlled LED Driver IC, which can control 10 LEDs according to the input voltage at the signal pin.
The 10k potentiometer is used to set a reference voltage at the REF ADJ pin (IC pin 8) of the IC. In other words, it is used to adjust the sensitivity of the sensor.
This IC also has one interesting feature, it has two operating modes DOT mode and BAR mode. Slide Switch 2 (SW2) is used to change the Modes.
When the temperature around the LM35 sensor will increase then this IC gets high input voltage and the IC turn on the maximum number of LEDs. When the temperature around the LM35 sensor will increase then this IC gets high input voltage and the IC turn on the maximum number of LEDs. In contrast, when the temperature will decrease then this IC gets Low input voltage from the sensor, and the IC turn on the minimum number of LEDs.
