Week 6 Log: Physical Logic Gates (From Simulation to Reality)
Week 6 Log: Physical Logic Gates (From Simulation to Reality)
Project Status: ✅ Completed | Focus: Breadboarding, NPN Transistors & Hardware Logic
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Project Overview
Project Overview
This week was all about bridging the gap between digital theory and physical hardware. The objective was to learn how to read and interpret schematics from Tinkercad and circuit simulators, and then bring those diagrams to life on a real physical breadboard.
My specific task was to manually construct AND and OR logic gates from scratch using discrete NPN transistors. This project proved that before there were microchips, computers were just clever arrangements of switches and wires!
The Hardware Stack (BOM)
The Hardware Stack (BOM)
To build these logic gates on the breadboard, I utilized the following physical components:
Power Supply: 9V Battery
Semiconductors: 2x BC547 Transistors (NPN)
Visual Output: 3x LEDs (Including 1 Green LED for the final logic output)
Passives (Resistors): 2x 220Ω, 2x 10kΩ, 1x 450Ω, and 1x 5kΩ
Input: 2x Physical Push Buttons
The Build Process: The AND Gate (Series Logic)
The Build Process: The AND Gate (Series Logic)
An AND gate requires both buttons to be pressed to output a signal. This means wiring the transistors in series to create a sequence of physical checkpoints.
1. LED Configuration
First, I mounted the three LEDs onto the breadboard.
I connected the negative legs (cathodes) of the first two input LEDs directly to the ground rail (-).
Hardware Note: The third LED (the Green output indicator) had to be intentionally flipped (right leg on the left) to align properly with the flow of the transistor output.
2. Transistor Assembly (The Series Path)
I seated the two BC547 transistors on the board.
To create the AND logic, I connected the 1st leg (Collector) of the first transistor to the positive rail (+).
I then jumpered the 3rd leg (Emitter) of the first transistor directly to the 1st leg (Collector) of the second transistor.
Finally, the 3rd leg (Emitter) of the second transistor was wired to the positive leg of the Green output LED.
(The middle legs were left open for the input signal).
3. The Input Triggers
I added the push buttons and wired them through the resistor network to the middle legs (Base) of the transistors. Now, pressing both buttons allows the 9V current to flow all the way to the Green LED.
Swipe through the carousel below to see the physical wiring steps side-by-side with the Tinkercad and circuit simulator references.
The OR Gate Modification (Parallel Logic)
The OR Gate Modification (Parallel Logic)
An OR gate requires either button to be pressed to trigger the LED.
The beauty of a breadboard is that changing the physical logic is incredibly fast. I didn't have to rebuild the entire circuit. By simply repositioning the blue wire and changing the path of the white wire, I broke the series connection and rewired the transistors in parallel. Now, pressing either button provides an independent physical path for the power to reach the Green LED.
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