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.
Found in an English Maplin magazine in 1983, this circuit has an RIAA equalization. We suggest its...
We found this circuit in a 1991s PE Hobbyst Handbook. The circuit fires 10 LEDs that can control...
This alarm with NO and NC sensors was found in the January 1975 Radio Electronics magazine. The...