Temperature gauge circuit using the LM324 IC

The temperature level is displayed using 4 LEDs:
A green LED indicates that the temperature is OK.
Two yellow LEDs indicate that the temperature is higher than normal.
A red LED indicates that the temperature is very high

Car battery monitor circuit using 4 LEDs

This simple Car battery monitor, allow us to know the voltage of the battery at all times. To achieve this 4 leds are placed somewhere on the dash of the car. Each LED has a label indicating the battery voltage at that time.