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 circuit was obtained in a publication for radio amateurs of 1977. It is used to reduce the...
This latching alarm using SCR was found in a Popular Electronics from 1992. The circuit triggers a...
This temperature alarm has maximum and minimum settings. We found it in the September 1971 Radio...