Exercise 5.3: Ripple Carry Adder

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1) 4-Bit Ripple Carry Adder

A single Full Adder calculates one column of numbers. To add two 4-bit numbers (like 1011 + 0110), we need to chain four Full Adders together.

The Ripple Effect

In this setup, the Carry Out of one adder becomes the Carry In of the next adder.

  • Bit 0 (LSB): Adds the 1s column. Its C_{in} is connected to Ground.
  • Bit 1: Adds the 2s column. It waits for the carry from Bit 0.
  • Bit 2: Adds the 4s column. It waits for the carry from Bit 1.
  • Bit 3 (MSB): Adds the 8s column. It outputs the final Overflow Carry.

Circuit Diagram

Figure 1: The Full Ripple Adder Circuit.

Build the Circuit

For this experiment, you are going to build the entire 4-bit calculator using only logic gates. This will be a complex build requiring careful wiring!

1. Build 4 copies of the Full Adder circuit you made in previous part.
2. Place them in a row on your breadboard(s).
3. Connect the Carry-Out of the first adder to the Carry-In of the second, and so on.
4. Connect the Carry-In of the very first adder to Ground (0V).
5. Connect 8xDIP switches for Number A (A0-A3) and 4 switches for Number B (B0-B3).
6. Connect 5 LEDs to the outputs (S0, S1, S2, S3 and Cout).
7. Connect all your DIP switches in 1kΩ pull down configuration, with bottom pins being constant High (5v).
8. Connect LEDs to ground through a 220Ω resistor.
9. Turn Power ON.
Figure 2: Example of the completed circuit. Note the DIP switch on the left and the 5 LEDs indicating the sum on the right.

If you perform the addition 1111 (15) + 0001 (1), what happens to the LEDs?

Final Submission

Upload a video (15 seconds) of your discrete logic 4-Bit Ripple Carry Adder working. Show the wiring complexity and a successful calculation like 1111 + 0001.
 No file selected

2) Miniaturization: The Adder IC

You probably noticed that building a 4-bit adder with individual gates uses a huge amount of wires and space. With so many connections, it is very easy to make a mistake!

In the real world, engineers rely on Integration. We can pack all those individual gates into a single chip (Integrated Circuit or IC), making the circuit smaller, faster, and more reliable.

The 74LS283

The 74LS283 is a 4-Bit Binary Full Adder IC. Inside this one small black chip are all the XOR, AND, and OR gates you just painstakingly wired up (or simulated).

Figure 2: 74LS283 4-Bit Binary Adder IC.

Key Features:

  • Inputs: It accepts two 4-bit numbers (A_1-A_4 and B_1-B_4) plus a Carry In (C_0).
  • Outputs: It produces a 4-bit Sum (S_1-S_4) and a final Carry Out (C_4).
  • Power: It requires 5V (VCC) and Ground (GND) to operate.
  • Speed: It performs the addition almost instantly, handling the "ripple" carry internally.

Build the Circuit

Now, let's build the clean version of the calculator using this chip.

1. Place the 74LS283 on the breadboard. Connect Pin 16 (VCC) to 5V and Pin 8 (GND) to Ground.
2. Connect the Carry In C0 pin (usually Pin 7) directly to Ground (To avoid floating input).
3. Connect your 8xDIP switches to the A and B inputs of the chip (A1-A4 and B1-B4).
4. Connect the Sum outputs (S1-S4) and the final Carry Out (C4) to your LEDs.
5. Connect all your DIP switches in 1kΩ pull down configuration, with bottom pins being constant High (5v).
6. Connect LEDs to ground through a 220Ω resistor.
7. Turn Power ON.
Figure 3: Example of the completed 74LS283 circuit. Note the DIP switch on the left and the 5 LEDs indicating the sum on the right.

In your 74LS283 circuit, what happens if you disconnect the C0 (Carry In) pin from Ground and it floats 'High'?

Final Submission

Upload a video (15 seconds) of your 74LS283 circuit. Set the switches to calculate 5 (0101) + 3 (0011). The result on the LEDs should be 8 (1000) with the Carry Out OFF.
 No file selected

The Power of Miniaturization

Building a 4-bit adder with individual logic gates requires complex wiring and significant breadboard space. In last project, you replaced this bulky setup with the 74LS283 4-Bit Adder IC. This is made possible by Integration.

Instead of using discrete components, engineers create circuits intigrated inside the chip itself, hence called Intigrated Circuit (IC).

This miniaturization provides three key benefits:

  • Reduced Wiring: Permanent internal connections eliminate dozens of external jumper wires, minimizing human error.

  • Space Efficiency: A multi-chip circuit is compressed into a single, compact package.

  • Enhanced Performance: Shorter electrical pathways allow the chip to calculate faster and consume less power.

By replacing complex logic circuits with a single integrated component, you are experiencing the foundational technology that scales room-sized computers down to modern smartphones.