This type of answering machine was common at the time this circuit was published. Using two tape recorders, it was published in the June 1986 issue of Radio Electronics magazine.
We find this simple circuit in an English publication called Electronic Circuit Design no. 3 of...
An OR gate can be implemented with an LM3900 transconductance operational amplifier. The circuit is...
This circuit is from the 1977 RCA Linear Integrated Circuits Manual. The circuit has a...