Equipment of Test Op-Amp

At the time of S1 is closed input do not tumble operation amplifier hewed to reference tension alighted from by output tension and voltage divider R2/R3. current passing R1 applied to fill condenser C1 until tension at input tumbles reachs the same price with reference tension. Because amplifier works as comparator, hence output level will change situation causing yields a reference tension which its(the polarity at the oposite. Charging current for C1 then will flow with direction which at the oposite until new reference tension reached and all above cycle will be repeated.

If high output, transistor T1 will accompany and LED D1 would be active ( ON). This scheme requires negative and positive power allowance and works is good if attached two battery 9V.