Additional circuit diagram for measuring voltage with 555 frequency meter

555 additional circuit for measuring voltage with frequency meter

As shown in the figure, this circuit consists of 555, an astable multivibrator composed of R1, RP1, and C1, and an attenuation resistor. As a voltage-frequency converter, it can measure DC voltages from 0 to 5V.
Potentiometer RP1 determines that when the input voltage is 0V, the frequency meter reading is 0Hz; RP2 is used to adjust the frequency meter reading to 50Hz when the input voltage is 5V, that is, full range adjustment. This additional circuit enables measuring frequency instead of measuring voltage.
Frequency meter, also known as frequency counter, is an electronic measuring instrument specially designed to measure the frequency of the signal being measured. The frequency meter mainly consists of four parts: time base (T) circuit, input circuit, counting display circuit and control circuit.