In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. The circuit is pretty simple though very useful all the same.

In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. The circuit is pretty simple though very useful all the same.

T1 — BC547 NPN transistor. IC1 — NE555P timer chip. J1 — Four-pin male header. ... (IRED1) through its driver BC547 (T1) — a general-purpose NPN transistor. After construction, the center frequency ...