Relay 5V Always Contact when Use External Power Supply

Official Hardware UNO Family UNO R3
1

Hi, I have project to make Modbus Relay. I use Arduino Uno, TTL to RS485 (max485) module, and relay 1 CH. When programming and I upload the program to Arduino Uno, the relay work normal with no issue (use power from USB). But when I Use buck converter LM2596S Module for buck from 24 V to 5V, the relay always contact (not using power from USB). This relay use LOW trigger to contact. Here the program and the wiring diagram

#include <SoftwareSerial.h>
#include <ModbusRTUSlave.h>

const uint8_t rxPin = 10; //for RO
const uint8_t txPin = 11; //for DI
const uint8_t dePin = 13; //for DE_RE

SoftwareSerial ModbusSer(rxPin, txPin);
ModbusRTUSlave ModbusSlave(ModbusSer, dePin); // serial port, driver enable pin for rs-485 (optional)

bool coils[8] = {0, 0, 0, 0, 0, 0, 0, 0}; // Initiation Coil Status
const int pinD4 = 4; //For Trigger Relay

void setup() {
  pinMode(pinD4, OUTPUT);

  ModbusSlave.configureCoils(coils, 8);                       // bool array of coil values, number of coils
  Serial.begin(9600);
  ModbusSlave.begin(2, 38400);                                // slave id, baud rate, config (optional)
}

void loop() {
  ModbusSlave.poll();
  if (coils[0] == 1)
  {
    digitalWrite(pinD4, LOW);
  }
  else
  {
    digitalWrite(pinD4, HIGH);
  }

}

Wiring Relay Modbus
Wiring Relay Modbus1191×605 9.45 KB

Best Regards

Caraka Tri

2

The '2596 output should not go to VIN, but to "5V".

3

Wow. It's work normal. Thankyou. Why output from 2596 should go to 5V, not to Vin?

4

VIN is for "8V", minimum. It is basically the equivalent of the barrel jack, but the barrel jack is fuse protected.

5

Thankyou @anon85221860 you're very helpful' :+1:t4: