7 Segment Digital Thermometer using ATtiny 85

This is a complete DIY project which requires a handful of components such as the ATtiny 85, LM35,MAX7219 and a couple of resistors and capacitors running off a regulated 5 V supply.
Temperature Measurement Range : 0 to 150’C
32 to 300’F
Controller: ATtiny 85
Display type – 4 digit multiplexed 7 segment display(Common Cathode type)
Programming Language: Arduino
The setup can display both in Celsius and Fahrenheit. By default the temperature is shown in Celsius but can be toggled to display in Fahrenheit using the push button.

Step 1: Working

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius temperature. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±1⁄4°C at room temperature and ±3⁄4°C over a full −55 to +150°C temperature range. The LM35’s low output impedance,linear output, and precise inherent calibration make interfacing to MCU easy.As it draws only 60 μA from its supply, it has very low self-heating, less than 0.1°C in still air.

7 Segment Digital Thermometer

The MAX7219 is a compact, serial input/output common-cathode display drivers that interface microprocessors (µPs) to 7-segment numeric LED displays of up to 8 digits. It  implements a SPI compatible slave interface that can be controlled from the Arduino using only 3 of the digital output pins.
All the necessary calculations and control signals are generated by the ATtiny85. The Data, CLK & Load pin of MAX7219 is connected to pin 2,1,0 of the ATtiny85 respectively. Analog output from LM35 is feed to the ADC channel 3 of the ATtiny85.

For more detail: 7 Segment Digital Thermometer using ATtiny 85

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