2.2.1. AND gate experiment

Components:

  • breadboard
  • 5V power supply
  • 3mm red LED
  • 2 x SPST pushbutton switches
  • 2 x BC547 NPN transistors
  • 220Ω, 2 x 2.2KΩ resistors
Figure 2-5 Transistor realization of AND gate

Explanation: Pressing the first and second pushbutton at the same time drives the transistors to saturation and they behave as closed switches. In that case, the current finds its path to the ground through the emitter and the LED is lit.

Now that we have built AND gate with transistors, we can use the TTL chip 7408. The chip contains four AND logic gates, connected according to the figure below.

Figure 2-6 Chip 7408
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