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 American 90’s documentation, this circuit generates 300 Hz depending on the capacitors...
According to what is said, the bugs are the female insects (mosquitoes, muriçocas and others)....
Found in a 90s nHands On Electronics, this circuit triggers a relay that shuts off the load when...