Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
This 80s signal follower makes use of an audio amplifier of the era. The circuit can be adapted to...
The circuit shown is only for analog telephone lines. I found it in Popular Electronics (1991). It...
We found this circuit in a 1977 CMOS oscillators documentation. The power can be sourced with...