Patent ID: 8729884

Claim:
A voltage measuring circuit comprising: a voltage measuring port for receiving an external voltage to be measured; a voltage reference unit with a port providing a reference voltage; a first voltage comparing unit with a reference port connected to the voltage reference unit, a measuring port connected to the voltage measuring port, and an output port , the voltage reference unit being connected between an external voltage port and the first voltage comparing unit, the output port outputting a high level voltage when the external voltage is lower than the reference voltage, the output port outputting a low level voltage when the external voltage is higher than the reference voltage; a first light emitting diode with a cathode connected to the output port of the first voltage comparing unit and an anode connected to the external voltage port; a second voltage comparing unit with a reference port connected to ground and the voltage reference unit respectively by a fourth resistor and a fifth resistor, a measuring port connected to the voltage measuring port, and an output port for outputting a high level voltage when the external voltage is lower than the voltage of the reference port of the second voltage comparing unit, the output port outputting a low level voltage when the external voltage is higher than the voltage of the reference port of the second voltage comparing unit; and a second light emitting diode with a cathode connected to the output port of the second voltage comparing unit and an anode connected to the external voltage port.