利用74LS138、与非门、74LS47和共阳极数码管(或74LS48和共阴极数码管）设计1位全加器。 要求 、 分别表示两个加数， 表示低位的进位， 和 分别表示和位以及向高位的进位，要求利用数码管显示输出结果。例如当输入 、 、 时，数码管应显示为3。

首先，根据全加器的逻辑电路图，我们可以得到以下真值表：

| A | B | Cin | Cout | S |
| :---: | :---: | :-: | :--: | :---: |
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | 1 |
| 0 | 1 | 0 | 0 | 1 |
| 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 | 0 |
| 1 | 1 | 0 | 1 | 0 |
| 1 | 1 | 1 | 1 | 1 |

根据真值表，我们可以得到以下逻辑式：

S = A xor B xor Cin

Cout = (A and B) or (Cin and (A xor B))

接下来，我们使用74LS138实现选择器，将输入的A、B、Cin和输出的S、Cout分别选择到不同的与非门中进行计算。具体电路如下图所示：


其中，74LS138的输入端A0、A1、A2分别连接A、B、Cin，输出端Y0、Y1、Y2、Y3分别连接与非门的输入端，74LS138的使能端G1、G2A、G2B均连接高电平，74LS47的输入端a、b、c、d、e、f、g分别连接与非门的输出端（注意，74LS47的输入端需要接入反向电阻，否则显示的数字会倒过来），74LS47的输出端a、b、c、d、e、f、g分别连接共阳极数码管的a、b、c、d、e、f、g。如果使用74LS48和共阴极数码管，则需要将74LS47改为74LS48，并将共阳极数码管改为共阴极数码管。

最后，我们可以使用以下代码在Arduino上实现该电路的功能：

const int A_pin = 2;
const int B_pin = 3;
const int Cin_pin = 4;
const int S_pin = 5;
const int Cout_pin = 6;

const int a_pin = 7;
const int b_pin = 8;
const int c_pin = 9;
const int d_pin = 10;
const int e_pin = 11;
const int f_pin = 12;
const int g_pin = 13;

void setup() {
  pinMode(A_pin, INPUT);
  pinMode(B_pin, INPUT);
  pinMode(Cin_pin, INPUT);
  pinMode(S_pin, OUTPUT);
  pinMode(Cout_pin, OUTPUT);
  pinMode(a_pin, OUTPUT);
  pinMode(b_pin, OUTPUT);
  pinMode(c_pin, OUTPUT);
  pinMode(d_pin, OUTPUT);
  pinMode(e_pin, OUTPUT);
  pinMode(f_pin, OUTPUT);
  pinMode(g_pin, OUTPUT);
}

void loop() {
  int A = digitalRead(A_pin);
  int B = digitalRead(B_pin);
  int Cin = digitalRead(Cin_pin);

  int S = (A ^ B ^ Cin);
  int Cout = ((A & B) | (Cin & (A ^ B)));

  digitalWrite(S_pin, S);
  digitalWrite(Cout_pin, Cout);

  if (S == 0b00000001) {
    digitalWrite(a_pin, LOW);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, LOW);
    digitalWrite(e_pin, LOW);
    digitalWrite(f_pin, LOW);
    digitalWrite(g_pin, LOW);
  } else if (S == 0b00000010) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, LOW);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, HIGH);
    digitalWrite(f_pin, LOW);
    digitalWrite(g_pin, HIGH);
  } else if (S == 0b00000011) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, LOW);
    digitalWrite(f_pin, LOW);
    digitalWrite(g_pin, HIGH);
  } else if (S == 0b00000100) {
    digitalWrite(a_pin, LOW);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, LOW);
    digitalWrite(e_pin, LOW);
    digitalWrite(f_pin, HIGH);
    digitalWrite(g_pin, LOW);
  } else if (S == 0b00000101) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, LOW);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, LOW);
    digitalWrite(f_pin, HIGH);
    digitalWrite(g_pin, HIGH);
  } else if (S == 0b00000110) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, LOW);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, HIGH);
    digitalWrite(f_pin, HIGH);
    digitalWrite(g_pin, HIGH);
  } else if (S == 0b00000111) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, LOW);
    digitalWrite(e_pin, LOW);
    digitalWrite(f_pin, LOW);
    digitalWrite(g_pin, LOW);
  } else if (S == 0b00001000) {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, HIGH);
    digitalWrite(f_pin, HIGH);
    digitalWrite(g_pin, HIGH);
  } else {
    digitalWrite(a_pin, HIGH);
    digitalWrite(b_pin, HIGH);
    digitalWrite(c_pin, HIGH);
    digitalWrite(d_pin, HIGH);
    digitalWrite(e_pin, HIGH);
    digitalWrite(f_pin, HIGH);
    digitalWrite(g_pin, LOW);
  }
}