Logic Gate Full Adder

ESP32 DevKit (WROOM-32)·Arduino C++·Updated Jul 27, 2026·by FluxBench TeamIncludes Lab + Schematic + PCB

The next step after the half adder: a 1-bit FULL adder built from five 74HC-style gate modules — two XORs, two ANDs and an OR — where gate outputs feed other gate inputs through a depth-3 network that the Lab solves from real voltages. The ESP32 drives A, B and carry-in from three GPIOs, reads SUM and CARRY back, and verifies all eight truth-table rows live; two LEDs show the result on the bench. Pull any wire mid-run and the chain genuinely breaks. Bundled Lab bench, schematic and routed PCB included.

sketch.ino

// Logic Gate Full Adder - five gates compute A + B + Cin
// P = A XOR B, SUM = P XOR Cin, CARRY = (A AND B) OR (P AND Cin)
#define PIN_A 25
#define PIN_B 26
#define PIN_CIN 27
#define PIN_SUM 32
#define PIN_CARRY 33

int combo = 0;
int errors = 0;

void setup() {
  Serial.begin(115200);
  pinMode(PIN_A, OUTPUT);
  pinMode(PIN_B, OUTPUT);
  pinMode(PIN_CIN, OUTPUT);
  pinMode(PIN_SUM, INPUT);
  pinMode(PIN_CARRY, INPUT);
  Serial.println("Full adder trainer: A + B + Cin = CARRY,SUM");
  Serial.println(" A B Cin | SUM CARRY");
}

void loop() {
  int a = (combo >> 2) & 1;
  int b = (combo >> 1) & 1;
  int cin = combo & 1;
  digitalWrite(PIN_A, a);
  digitalWrite(PIN_B, b);
  digitalWrite(PIN_CIN, cin);
  delay(60); // let the gate chain settle
  int sum = digitalRead(PIN_SUM);
  int carry = digitalRead(PIN_CARRY);
  int total = a + b + cin;
  int wantSum = total & 1;
  int wantCarry = (total >> 1) & 1;
  Serial.print(" ");
  Serial.print(a);
  Serial.print(" ");
  Serial.print(b);
  Serial.print("  ");
  Serial.print(cin);
  Serial.print("  |  ");
  Serial.print(sum);
  Serial.print("    ");
  Serial.print(carry);
  if (sum == wantSum && carry == wantCarry) {
    Serial.println("   ok");
  } else {
    Serial.println("   MISMATCH");
    errors++;
  }
  combo++;
  if (combo == 8) {
    if (errors == 0) {
      Serial.println("All 8 rows verified - full adder works!");
    } else {
      Serial.println("Check your wiring - mismatches found.");
    }
    combo = 0;
    errors = 0;
    Serial.println(" A B Cin | SUM CARRY");
  }
  delay(1440);
}

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