Experiment 12 - The NOT Circuit

The simplest logic operation is the NOT logic. The corresponding logic unit has only one input and one output. That you can easily replace it with a transistor circuit.

The truth table shows you the NOT-logic. The result at the output Q negates the input A...

A Q 0 1 1 0 Truth Table of the NOT logic.

NOT symbol in circuit diagrams.

Transistor circuit of a NOT logic unit. (Enlarge)

Circuit diagram of NOT logic with a transistor.

Now you replace the integrated circuit (IC) from the last experiment by the transistor circuit shown.

• When the pushbutton switch is open (A = 0), the transistor is blocked and current flows through the resistor R2a and Q. The LED lights up (Q = 1).
• When you press the pushbutton switch (A = 1), the transistor switches through and hence shortcircuits Q. The LED goes dark (Q = 0).

This is the logical behavior of a NOT unit.