Learn transistor circuit works, old parts But, we often use it. Because of durable, high current. Whether any reason. Let's learn they works in simple way.
LED VU meter using transistor is analog circuit to show level of power audio signal. You can build 5 LED to 20 LED display with PCB.
See and try building Lie detector circuit. The resistance of human skin using transistors and LED displays is small and easy application.