Annex: Labs and Arduino Resources

🏠 Home

The course has four hands-on labs. Each idea is done twice: once in the LogicLab simulator, and once on a breadboard with real ICs and an Arduino. Two labs are combinational (the half adder) and two are sequential (the 2-bit counter).

Equipment

An Arduino (used as a 0 to 5V supply and as a digital instrument that drives inputs and reads outputs), a breadboard and jumper wires, LEDs with about 330 ohm resistors, and these logic ICs: 74HC86 (quad 2-input XOR), 74HC08 (quad 2-input AND), and 74HC74 (dual D flip-flop).

Lab 1: Half adder in LogicLab

Goal: build a half adder and confirm its truth table in the simulator.

Place two input switches A and B, an XOR gate (its output is the sum S) and an AND gate (its output is the carry C), and two LEDs. Wire A and B into both gates, power it, and toggle A and B through 00, 01, 10, 11. Confirm S = A XOR B and C = A AND B.

▶ Open the half adder in LogicLab

Lab 2: Half adder with Arduino and logic ICs

Goal: build the same half adder on a breadboard and check it against Lab 1.

Wiring. Power the ICs from the Arduino’s 5V and GND rails. Use one gate of a 74HC86 for the sum and one gate of a 74HC08 for the carry. Drive A and B from two Arduino output pins, feed both into the XOR gate (output S) and the AND gate (output C), and read S and C on two Arduino input pins (or show them on LEDs through 330 ohm resistors).

Sketch. This drives all four input combinations and prints the truth table:

const int A=2, B=3, S=4, C=5;
void setup(){
  pinMode(A,OUTPUT); pinMode(B,OUTPUT);
  pinMode(S,INPUT);  pinMode(C,INPUT);
  Serial.begin(9600);
  Serial.println("A B | S C");
  for(int a=0;a<2;a++) for(int b=0;b<2;b++){
    digitalWrite(A,a); digitalWrite(B,b); delay(50);
    Serial.print(a); Serial.print(" "); Serial.print(b); Serial.print(" | ");
    Serial.print(digitalRead(S)); Serial.print(" "); Serial.println(digitalRead(C));
  }
}
void loop(){}

The printed table should match the one from Lab 1.

Lab 3: 2-bit counter in LogicLab

Goal: build a 2-bit synchronous up-counter and watch it count.

Place two D flip-flops sharing one clock. Wire D0 = Q0' (feed FF0’s Q’ back to its own D) and D1 = Q1 XOR Q0. Put LEDs on Q0 and Q1. Power it and press the clock’s single-step button: the count should walk 00, 01, 10, 11, 00.

▶ Open the 2-bit counter in LogicLab

Lab 4: 2-bit counter with Arduino and ICs

Goal: build the same counter on a breadboard and check it against Lab 3.

Wiring. Power a 74HC74 (two D flip-flops) from 5V and GND, and tie both clock inputs to a common clock line driven by an Arduino pin. For FF0, connect its Q’ output back to its own D so it toggles every clock. For FF1, drive D1 from a 74HC86 XOR of Q1 and Q0. Read Q0 and Q1 on Arduino input pins, or show them on LEDs.

Sketch. This generates the clock and prints the count each cycle:

const int CLK=2, Q0=4, Q1=5;
void setup(){
  pinMode(CLK,OUTPUT); pinMode(Q0,INPUT); pinMode(Q1,INPUT);
  Serial.begin(9600);
}
void loop(){
  digitalWrite(CLK,HIGH); delay(250);
  digitalWrite(CLK,LOW);  delay(250);
  int count = (digitalRead(Q1)<<1) | digitalRead(Q0);
  Serial.println(count);   // expect 0,1,2,3,0,1,2,3,...
}

Using the Arduino as a bench tool

You do not program the Arduino as the subject of the course; you use it to power and probe the logic you built. Two patterns cover both labs:

The Serial Plotter is useful for watching several signals change over time.

Beyond the labs: the MCU cross-check

To show the final MCU is not a toy, the same six-instruction program it runs can be written as an Arduino sketch (LDA, LDB, ADD, SUB, STS, NOP as a tiny interpreter). Running it both ways gives the same result, which is the point: the gate-level machine and a real MCU do the same thing.