LED voltage measurement circuit diagram

This circuit uses light-emitting diodes to indicate voltages at four different levels. The RS339 in the circuit is a four-comparator. When the input voltage exceeds the reference voltage of a certain comparator, the comparator and the comparators below it all output low level, and the corresponding light-emitting tube emits light to indicate the level of the input voltage.

LED1 is a zero-point voltage indicating light-emitting diode. As the voltage reference point of this circuit, it is always on.