This resistance meter was found in an English documentation from 1989. The operational amplifier admits an equivalent and the transistor can be a BC558 or BC559.
This oscillator from an old publication uses one of the first commercial transistors, the CK722....
The integrated circuit used in this configuration is not common today. The zener determines the...
With good filtration, a battery charger can be used as a power source. The filter shock can be the...