555 ultra-low frequency millivolt signal generator circuit diagram

The circuit is shown in the figure. The generator consists of an oscillator, voltage follower, amplitude zero adjustment, zero point migration circuit, etc. Used as a signal source for the automatic balance recorder operation test, the output signal is 0~50mV, the zero point shift of the output voltage is continuously adjustable by plus or minus 25mV, and the cycle rate is 30~40Hz.

IC1 (555) and VT1, VT2, R1, R2, and C form an astable multivibrator. VT1, R1, VT2, and R2 form charge and discharge constant current sources respectively. IC2 operational amplifier is used as a voltage follower, mainly used for impedance matching and low impedance output. The output voltage V0=V01-V02, by adjusting RP1 and RP2, the amplitude zero adjustment and level migration can be achieved.