4-Bit Adding Circuit With Digital Results Display

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This is a simple project that explains how to build a 4-bit adding circuit (4-bit adding calculator) made of seven segment displays, seven segment drivers, AND, OR, NOT, and EXOR gates that add two 4-bit numbers together and returns the results. It is a great project to help beginning electronic/computer students and hobbyist understand how to build combinatorial logic circuits from logic gates to perform a given function. In the case of this project, the function is an adding calculator.

Above is a video explaining how the circuit works, a system block diagram showing the modules used to compose the calculator and their connection to other modules. Also shown above is a picture shows the location of the modules on the circuit I built.

Each of the following steps will show how to build the circuit in modules. To demonstrate this, each step will include:

  • a picture showing the location of the modules on my circuit and/or
  • schematic diagram required to build that module(s) for the circuit.

Note:

  1. Full schematic diagrams included at the end of this Instructable.
  2. You may find the following links to videos useful when placing components on the prototyping board.

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Supplies:

Required Supplies:

  • (1) 7404 - Hex Inverter/NOT gates
  • (3) 7408 - Quad 2-input AND gates
  • (2) 7411 - Triple 3-input AND gates
  • (2) 7432 - Quad 2-input OR gates
  • (4) 7448 - Seven Segment Display Driver
  • (2) 7486 - Quad 2-input EXOR gates
  • (4) Man 74A
  • (1) Light Emitting Diode (LED)
  • (8) SPDT switches
  • Prototyping board(s)
  • Connection wires
  • Power Supply
  • Important Datasheets:

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Step 1: Construct One Half-adder Circuit As Shown in the Schematic Below.

Notes: Connect the Vcc pin on each chip used to the 5V bus on the prototyping board. Connect the GND pin on each chip used to the gnd bus on the prototyping board.

Step 2: Construct Three Full-adder Circuit As Shown in the Schematic Below. Construct Them Close to the Half-adder From Step 1.

Notes: Connect the Vcc pin on each newly added chip used to the 5V bus on the prototyping board. Connect the GND pin on each newly added chip used to the gnd bus on the prototyping board.

Step 3: Construct the 4-bit Adder by Connect the 3 Full-adders and 1 Half-adder As Shown in the Block Diagram.

My 4-bit adder is enclose by a red square in the picture above.

Note: My 4-bit adder circuit has additional wires for other parts of the circuit that we will discuss in later steps.

Step 4: Construct the 4-bit Binary-to-BCD Circuit As Shown in the Schematic Diagram Below. Connect the 4-bit Binary-to-BCD Circuit to the 4-bit Adder As Shown in the Block Diagram at the Beginning of This Instructable.

My 4-bit binary-to-BCD circuit is shown in the red box in the image above.

Notes:

  • Connect the Vcc pin on each newly added chip used to the 5V bus on the prototyping board.
  • Connect the GND pin on each newly added chip used to the gnd bus on the prototyping board.
  • My 4-bit binary-to-BCD circuit has additional wires for other parts of the circuit that we will discuss in later steps.

Step 5: Construct 4 Seven-segment Display With Driver Circuits As Shown in the Schematic Below. Connect Two Seven-segment to the 4-bit Adder and Two to the 4-bit Binary-to-BCD Converter As Shown in the Block Diagram at the Beginning of This Instructable.

My 4 seven-segment display with driver circuits are shown in the red boxes in the image above.

Notes:

  • Connect the Vcc pin on each newly added chip used to the 5V bus on the prototyping board.
  • Connect the GND pin on each newly added chip used to the gnd bus on the prototyping board.
  • My 2 seven-segment display with driver circuits that are connected to the 4-bit adder have additional wires for other parts of the circuit that we will discuss in the next steps.

Step 6: Connect 8 SPDT Switches to Ground and Vcc As Shown in the Schematic Below. Then Connect the 8 SPDT Switches to the Two Lower Seven-segment Display and Driver Circuits As Well As the 4-bit Adder Circuit As Shown in the Block Diagram

Step 7: Connect an LED to the Co3 Output of the 4-bit Binary-to-BCD Converter Circuit As Show in the Block Diagram the Beginning of This Instructable.

My LED is shown in the red boxes in the image above.

Note: LEDs are not bi-polar. They must be connected correctly to work. Follow the schematic at the beginning of this instructable and you should be ok.

Step 8: Connect a Power Supply to the Vcc and Gnd Buses. Supply 5V to the Vcc Bus.

Step 9: Use the Table Below to Add Numbers. Move the Switches to Gnd (0) or Vcc (1) to Compose Desired Number.

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