How to increase the inputs and outputs of microcontrollers

This project integrates two key ICs: the 74HC4051 analog multiplexer/demultiplexer and the 74HC165 shift register, to efficiently control an 8-button input system and a PWM-controlled LED system. The 74HC165 shift register is used to read the state of up to 8 buttons with minimal GPIO usage, while the 74HC4051 multiplexer enables control of 8 LEDs using a single PWM pin. The system works by scanning each button, updating the corresponding LED state, and setting its brightness accordingly. When a button is pressed, the corresponding LED toggles between ON (full brightness) and OFF using an XOR operation. The PWM pin (D9) is used to control the LED brightness, ensuring efficient use of microcontroller resources. The entire system runs in a loop, continuously checking for button presses and updating LED states. This approach significantly reduces the number of pins needed on the microcontroller while maintaining precise control over multiple inputs and outputs.

Schematic:

Pin tables:

Code:

// File: combined_74hc4051_74hc165_shared_d5.ino

// 74HC4051 pins

#define A 2

#define B 3

#define C 4

#define PWM_PIN 9

// 74HC165 pins

#define SH_LD 5   // Shared Shift/Load Bar pin

#define CLK 6     // Clock pin

#define SO 7      // Serial Output pin

// Brightness levels

#define LED_ON 255

#define LED_OFF 0

// Store LED states (ON/OFF)

byte ledStates = 0;

void setup() {

  // 74HC4051 control pins

  pinMode(A, OUTPUT);

  pinMode(B, OUTPUT);

  pinMode(C, OUTPUT);

  // PWM output pin

  pinMode(PWM_PIN, OUTPUT);

  // 74HC165 control pins

  pinMode(SH_LD, OUTPUT);

  pinMode(CLK, OUTPUT);

  pinMode(SO, INPUT);

  Serial.begin(9600);

}

void loop() {

  // Read button states from 74HC165

  byte buttonStates = readShiftRegister();

  // Loop through each button/LED

  for (int i = 0; i < 8; i++) {

    // Check if button is pressed

    if ((buttonStates >> i) & 0x01) {

      // Toggle LED state

      ledStates ^= (1 << i); // XOR to toggle the bit

    }

    // Set the brightness for the corresponding LED

    selectChannel(i);

    if ((ledStates >> i) & 0x01) {

      analogWrite(PWM_PIN, LED_ON);

    } else {

      analogWrite(PWM_PIN, LED_OFF);

    }

    delay(30);

  }

  //delay(50); // Small delay for stability

}

// Function to read the shift register

byte readShiftRegister() {

  // Load parallel data into shift register

  digitalWrite(SH_LD, LOW);  // Activate parallel load

  delayMicroseconds(5);      // Wait for data to load

  digitalWrite(SH_LD, HIGH); // Set to shift mode

  byte data = 0;

  // Shift out the bits one by one

  for (int i = 0; i < 8; i++) {

    digitalWrite(CLK, LOW); // Pulse the clock to shift data

    delayMicroseconds(5);

    data |= (digitalRead(SO) << (7 - i)); // Read the SO pin and store the bit

    digitalWrite(CLK, HIGH);

  }

  return data;

}

// Function to select the active channel on the 74HC4051

void selectChannel(int channel) {

  digitalWrite(A, channel & 0x01);

  digitalWrite(B, (channel >> 1) & 0x01);

  digitalWrite(C, (channel >> 2) & 0x01);

}

Working Principle

1. Button State Reading (74HC165):

   • The Arduino first loads parallel data from the 8-button inputs into the 74HC165 shift register.
   • It then shifts out the data serially, reading each button state one by one.
   • If a button is pressed, its corresponding bit is set in the buttonStates variable.

2. LED Control (74HC4051):

   • The system loops through all 8 LEDs, using the 74HC4051 multiplexer to select which LED to control.
   • If the corresponding button is pressed, it toggles the LED ON/OFF using an XOR operation.
   • The LED brightness is set using PWM on pin D9, meaning the LED is either fully ON (255) or OFF (0).

3. Efficient GPIO Usage:

   • Instead of using 16 separate GPIO pins, the project uses just 6 digital pins for controlling 8 buttons and 8 LEDs.
   • The 74HC165 shift register allows reading multiple inputs through a single data pin.
   • The 74HC4051 multiplexer enables control of multiple LEDs using a single PWM pin.

This design is ideal for applications requiring efficient input reading and output control while minimizing pin usage on an Arduino or microcontroller.