As shown in FIG circuit by the voltage - frequency converter and an amplitude modulator. Input voltage V1 by the operational amplifier A1 control FET 2N4222 internal resistance
, thereby changing the astable multivibrator oscillation frequency. A2 is the amplitude modulator, modulated by the input signal V2 output. Let FET pinch-off voltage Vp,Tt (1 + R1/R2) Vp, the output and input of the relationship: Vo -V2/V1 V1 and V2 required range is 0 ~ 10V. Vo is the average output can be obtained through the filter, you can also use damped voltmeter readout.