2.4.1. OR 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 2‑11 Transistor realization of OR gate

Pressing any of the pushbuttons drives their transistor to 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 is lit.

We will further use the TTL chip 7432 containing four OR logic gates, according to the figure below.

Figure 2‑12 Chip 7432

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