How to extend the inputs and outputs of any microcontroller.

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This project uses two key ICs: the 74HC4051 analog multiplexer/demultiplexer and the 74HC165 shift register. It controls an 8-button input system and a PWM-controlled LED system. The 74HC165 shift register reads up to 8 buttonswith just a few GPIO pins. The 74HC4051 multiplexer controls 8 LEDs with one PWM pin. It scans buttons, updates LEDs, and sets their brightness. When a button is pressed, the LED toggles between ON (full brightness) and OFF using an XOR operation. The PWM pin (D9) controls LED brightness, saving microcontroller resources. The system runs in a loop, checking for button presses and updating LEDs. This method reduces pins needed while maintaining control over inputs and outputs.

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);
	}

view raw combined_74hc4051_74hc165_shared_d5.ino hosted with ❤ by GitHub

Schematic:

Proteus screenshot of the shifter, the multiplexer and the arduino uno

Pin connection table:

For the 74HC165

For the 74HC4051

Working Principle

Button State Reading (74HC165):
- The Arduino loads parallel data from 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.
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).
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.