Esp32 and 74hc595 problem

Hi all,

I am using 74hc595 in several projects where I need more I/O and always worked fine using arduino pro mini or arduino mega. Now I connected same 2 of 74hc595 to an esp32 and does not work.
Is there any special things to do for esp32?

Wiring is exactly the same like here on chapter 2 (Connect the 2 registers.). If I use this with an arduino mega on pins 10,9,8 (see commented in code) is working perfect.

Then I replace arduino mega with esp32 and using pins 23,18,5 and does nothing. I get in serial monitor on/off prints but nothing changes to the relays.


int SER_Pin = 23;//10; //pin 14 on 75hc595 //data pin
int RCLK_Pin = 18;//9; //pin 12  //latch
int SRCLK_Pin = 5;//8; //pin 11  //clock

#define number_of_74hc595s 2

#define numOfRegisterPins number_of_74hc595s * 8

boolean registers[numOfRegisterPins];

void setup() {
  pinMode(SER_Pin, OUTPUT);
  pinMode(RCLK_Pin, OUTPUT);
  pinMode(SRCLK_Pin, OUTPUT);


void clearRegisters() {

  for (int i = numOfRegisterPins -1; i >= 0; i--) {
    registers[i] =HIGH;

//Set and display registers
//Only call after all values are set how you would like 
void writeRegisters() {
   digitalWrite(RCLK_Pin, LOW);

   for (int i = numOfRegisterPins -1; i >= 0; i--) {
      digitalWrite(SRCLK_Pin, LOW);
      int val = registers[i];

      digitalWrite(SER_Pin, val);
      digitalWrite(SRCLK_Pin, HIGH);
  digitalWrite(RCLK_Pin, HIGH);

//set an individual pin high or low
void setRegisterPin (int index, int value) {
  registers[index] = value;

void c_on() {

void c_off() {

void loop() {


Is there any special thing to do for using esp32?

Thank you very much

ESP32 is a 3.3V device. What is supply voltage to the shift registers? What relays are you using, what is the spec?

Also, there are errors on the circuit on the page you mentioned. The 10uF cap is a good idea when driving LEDs, and maybe relay modules, especially those with opto-isolators. But there should additionally be a 0.1uF ceramic bypass cap between the Vcc and Gnd pins of each shift register.

The issue was from the power supply. Weird because same power supply worked with arduino mega…
Thanks a lot

So, this is a regulated 5 V power supply then? :roll_eyes: