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Project: RJT520 Relay Timer, 555, 6V to 18V, 20A

In this tutorial, we will build a relay timer circuit using the RJT520 relay and a 555 timer IC that operates within a voltage range of 6V to 18V. This project is ideal for controlling devices that require a delay before turning on or off, such as lights or appliances. The outcome will be a functional relay timer that can handle up to 20A of current, allowing for a wide range of applications.

We will utilize the 555 timer IC in monostable mode to create a delay timer. When triggered, the timer will activate the relay for a specified duration before turning it off. This project is simple yet effective, making it a great addition to your electronics toolkit. For a more visual explanation, be sure to check the video (in video at 02:15).

Hardware Explained

The main components of this project include the RJT520 relay, the 555 timer IC, and a power supply. The RJT520 relay is a high-power relay that can switch loads up to 20A, making it suitable for controlling larger devices. The 555 timer IC is a versatile component that can be configured in various modes, including monostable mode, which we will use for our timer.

The relay works by using an electromagnet to mechanically switch a set of contacts. When the 555 timer output goes high, it energizes the relay coil, closing the contacts and allowing current to flow to the connected load. This setup is beneficial for applications that require remote operation or automation.

Datasheet Details

• Ensure the relay can handle the load current (20 A max).
• Use appropriate heat sinking if the relay operates at high temperatures.
• Verify the voltage levels to avoid damaging the 555 timer.
• Use decoupling capacitors close to the 555 timer power pins.
• Check relay contacts for wear and replace if necessary.
• Be cautious of back EMF when switching inductive loads.

Wiring Instructions

To wire the RJT520 relay timer circuit, start by connecting the 555 timer IC. Connect pin 1 (GND) of the 555 timer to the ground of your power supply. Then, connect pin 8 (VCC) to the positive terminal of your power supply (6V to 18V).

Next, wire pin 2 (TRIG) to your trigger switch or input signal. This pin will activate the timer when it receives a low pulse. Connect pin 3 (OUT) of the 555 timer to one terminal of the relay coil, and connect the other terminal of the coil to the ground. Don't forget to add a diode across the relay coil to protect the circuit from back EMF.

For the relay output, connect one of the common terminals to the load you want to control, and the other terminal to the power source. Make sure to connect the load's other terminal back to the common ground. Finally, configure the timing components (resistor and capacitor) connected to pins 6 and 2 for your desired delay.

Code Examples & Walkthrough

In the code, we will define key identifiers such as triggerPin for the input trigger and relayPin for the relay output. The setup function initializes these pins, while the loop function monitors the trigger state.

const int triggerPin = 2; // Input trigger pin
const int relayPin = 3;    // Relay control pin

void setup() {
  pinMode(triggerPin, INPUT);
  pinMode(relayPin, OUTPUT);
}

void loop() {
  if (digitalRead(triggerPin) == HIGH) {
    digitalWrite(relayPin, HIGH); // Activate relay
    delay(1000);                  // Keep relay on for 1 second
    digitalWrite(relayPin, LOW);  // Deactivate relay
  }
}

This excerpt initializes the pins and sets the relay to activate for one second whenever the trigger pin receives a HIGH signal. Make sure to adjust the delay for your specific timing requirements.

void loop() {
  if (digitalRead(triggerPin) == HIGH) {
    digitalWrite(relayPin, HIGH); // Activate relay
    delay(1000);                  // Keep relay on for 1 second
    digitalWrite(relayPin, LOW);  // Deactivate relay
  }
}

Here, we check if the triggerPin is HIGH. If it is, we turn on the relay and keep it activated for one second using the delay() function. Adjust the delay as necessary for your application.

Demonstration / What to Expect

Upon successful wiring and programming, the relay should activate when the trigger is engaged. You can test various loads to ensure the relay operates correctly within its rated specifications. Common pitfalls include incorrect voltage connections and failure to protect against back EMF, which can damage the circuit.

Video Timestamps

• 00:00 - Introduction
• 02:15 - Wiring Explanation
• 05:30 - Code Walkthrough
• 07:45 - Demonstration

Images

Relay Timer 555 6V to 18V 20A PCB 1

Relay Timer 555 6V to 18V 20A PCB 2

Relay Timer 555 6V to 18V 20A PCB 3

Relay Timer 555 6V to 18V 20A PCB Gerber file 4

Relay Timer 555 6V to 18V 20A PCB Gerber file 5

Relay Timer 555 6V to 18V 20A PCB Gerber file 6

Relay Timer 555 6V to 18V 20A PCB Gerber file 7

Relay Timer 555 6V to 18V 20A PCB Gerber file 8

Relay Timer 555 6V to 18V 20A PCB Gerber file 9

555 Relay Timer of 20A 0-10 minutest on breadboard wiring

Relay Timer 555 6V to 18V 20A PCB 1

Relay Timer 555 6V to 18V 20A PCB 2

Relay Timer 555 6V to 18V 20A PCB 3

Relay Timer 555 6V to 18V 20A PCB Gerber file 4

Relay Timer 555 6V to 18V 20A PCB Gerber file 5

Relay Timer 555 6V to 18V 20A PCB Gerber file 6

Relay Timer 555 6V to 18V 20A PCB Gerber file 7

Relay Timer 555 6V to 18V 20A PCB Gerber file 8

Relay Timer 555 6V to 18V 20A PCB Gerber file 9

555 Relay Timer of 20A 0-10 minutest on breadboard wiring