2.5.1. NOR 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 2‑14 Transistor realization of NOR gate

Explanation: Pressing any of the pushbuttons drives their transistor in saturation and it behaves like a closed switch. In that case, the current finds its path to the ground through the emitter and the LED turns off.

We will further use TTL chip 7402 which contains four NOR logic gates, organized according to the figure below.

Figure 2‑15 Chip 7402

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