This a voltage controlled oscillator is designed with OP80 operational amplifier.
Integrator designed with OP80, serves as a voltage controlled oscillator and is not affected by the polarity of the control voltage. If a continuous input voltage is applied to the circuit, C1 will charge, depending on the polarity of the input voltage, C1 potential and, thus, the output voltage of IC1 will be positive or negative.
The signal from the output of IC1 is applied to a window comparator with a threshold switching has both positive signal, and for the negative. These levels are set at ± 100 mV, with P2.
A proper sizing of R1 will allow you to set the ratio of voltage and frequency (for example, the value of 1 Hz / mV). With input shorted, set P1 for the lowest possible frequency output signal (ideally, f = 0). Maximum input voltage amplitude is determined by IC2's output current (15 mA) and can reach up to 15 x 10 -3 x R1.
On leaving the oscillator will get a sawtooth signal with a frequency of up to 10 kHz.
Frequency as a function of input current is given by: Iin / (UvfxC1) [Hz] (with the component values given in the scheme: f = Iin / (3.9 x 10 ^ -10) [Hz]).
Voltage of the amplifier OP80 should not exceed ± 8 V (typical current through the assembly, will be 4 mA).