User manual

26
13 Touch switch
We add another transistor to the first to increase amplifica-
tion even more. Both collector terminals are interconnected;
the emitter of the first transistor goes to the base of the sec-
ond. This circuit is called Darlington circuit. We will use this
to build a touch switch. When you touch the free end of the
wire and the 330 kΩ resistor at the same time with your fin-
gers, a very small current, too small for you to feel, will flow
through your finger and amplify to the point that both LEDs
are turned on.
Until now we left our first transistor in its initial position. To-
day we have to install it differently, so that both transistors fit
properly. The new input is the base of the left transistor.