This circuit is mainly composed of two integrated operational amplifiers LM324. One LM324 contains four identical operational amplifiers. The circuit uses two LM324s to form an 8-level voltage comparator. Each op amp is connected to a voltage comparator.
The comparator inverting input is divided by a series resistor, and the voltage is stepped into the inverting input of the voltage comparator from low to high. The thermistor is a negative temperature coefficient thermistor. The higher the temperature, the lower the resistance.
The thermistor is connected in series with a fixed resistance resistor, which is connected in series to the non-inverting input of the voltage comparator. When the temperature rises, the thermistor resistance becomes smaller, the series voltage on it rises, and the voltage exceeds the voltage of the inverting input terminal, the voltage comparator outputs a high level, and the corresponding LED lights up.
The higher the temperature, the higher the output. The more voltage comparators of the level, the more the LEDs illuminate, indicating the temperature. The adjustable resistor R1 can adjust the range of temperature indication.
Tested by ICStation's Outstanding Partner bzoli5706 and his friends: (The language in the video isEnglish)
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