Touch Sensor using BC547

BC547 is an NPN bipolar junction transistor. A transistor stands for transfer of resistance, is commonly used to amplify current. A small current at its base controls a larger current at collector & emitter terminals.

Figure 1:- Working Principle of BC547

Figure 2:- BC547 Transistor

Figure 1 consists of two bipolar transistors (BC547), where the emitter of the transistor (T1) is connected to the base of the other transistor (T2). Therefore, the current amplified by the T1 is amplified further by the transistor T2. However, the collectors of both T1 and T2 are connected with each other. If we make the arrangement of transistors as shown in figure 1 then there will be a much higher current gain than each transistor taken separately. This was invented by Sidney Darlington in 1953.

If we connect two transistors as illustrated in figure 1 then the whole circuit behaves like a single transistor. That means it acts like one base, collector, and emitter.