Summary of Digital thermometer using arduino and LM35
This article describes a simple three-digit digital thermometer project using an Arduino and LM35 sensor. It measures temperatures from 0°C to 99.9°C with an optional Fahrenheit display. The LM35 sensor operates between -55°C and +155°C, outputting 10mV per °C. The circuit connects the sensor to analog pins, uses a switch for unit selection on pin 4, and drives a multiplexed 7-segment display via transistors and resistors.
Parts used in the Digital Thermometer Project:
- Arduino board
- LM35 temperature sensor
- Digital 7-segment display
- Transistors Q1, Q2, Q3
- °C/°F selector switch
- Resistors R1 through R11
This article is about a simple three digit digital thermometer using arduino. Range of this thermometer is from 0°C to 99.9°C. There is also a provision for displaying the temperature in °F scale. Three terminal analog temperature sensor LM35 is used as the sensor here. LM35 can measure temperatures between -55°C to +155°C. The supply voltage range is from 4V to 30V DC and the current drain is 60uA. The LM35 is available in TO-92 package and it is very easy to use. The output voltage of the arduino increases 10mV per °C rise in temperature. That means if 25 °C is the temperature, then output voltage of the sensor will be 250mV. Circuit diagram of the digital thermometer using arduino and LM35 is shown in the figure below.
Circuit diagram.
Temperature sensor LM35 is connected to the arduino through the analog input pins. A0 pin of the arduino serves as the supply voltage source for LM35 and A2 pin of the arduino serves as the ground. Arduino reads the voltage output of the LM35 through the analog input pin A1. Digital pin 4 is used for interfacing the °C/°F selector switch to the arduino. Digit driver transistors Q1, Q2 and Q3 are interfaced to the digital pins 1, 2 and 3 of the arduino respectively. Multiplexed segment lines a to dp are interfaced to the digital pins 5 to 12 of the arduino respectively. Resistors R9, R10 and R11 limits the base current of the corresponding transistors. Resistors R1 to R8 limits the current through the corresponding segments.
Read More: Digital thermometer using arduino and LM35
- What is the measurement range of this thermometer?
The thermometer displays temperatures from 0°C to 99.9°C. - Can the device display temperature in Fahrenheit?
Yes, there is a provision for displaying the temperature in °F scale. - How does the LM35 sensor output voltage change?
The output voltage increases by 10mV for every 1°C rise in temperature. - Which Arduino pin connects to the Celsius or Fahrenheit selector switch?
Digital pin 4 is used for interfacing the °C/°F selector switch. - How are the segment lines connected to the Arduino?
Multiplexed segment lines a to dp are interfaced to digital pins 5 to 12. - What is the function of resistors R9, R10, and R11?
These resistors limit the base current of the corresponding transistors Q1, Q2, and Q3. - What is the current drain of the LM35 sensor?
The current drain is 60uA. - Which Arduino pin serves as the ground for the LM35?
A2 pin of the Arduino serves as the ground for the sensor.
