If the battery is good, the LED flashes. This simple tester uses an LM3909 integrated circuit. We found this configuration in an old documentation.
This touch sensor, found in an American documentation on transistors, has gained 8 million times...
The block shown in the figure is a basic source with a configuration widely used in technical...
The output of this circuit must be connected to the input of an audio amplifier. The microphone is a small...