Introduction

In the world of DIY electronics, there are countless projects that require converting power from one voltage level to another. One common example is when you need to power low-voltage components such as LEDs or microcontrollers from a 12V DC source. In this project, we’ll be designing and building a simple but effective 12V to 5V LED power supply using the S2-12V relay.

The S2-12V relay is a widely used electromagnetic relay designed to control high-power circuits with low-power control signals. It can be used in a variety of applications, such as switching devices on and off in response to logic-level signals. In this particular project, we’ll use the relay to switch the power to an LED circuit that requires a stable 5V supply, providing the necessary voltage conversion in an efficient and simple manner.

This project is ideal for beginners and intermediate electronics enthusiasts who want to create a practical power supply for their DIY electronics projects. The circuit will involve basic components like the S2-12V relay, a voltage regulator, resistors, capacitors, and LEDs, and it will not require any programming or microcontroller control. Instead, the focus will be on how to use the relay and associated components to manage the power conversion and switching process.

Components Needed

To build this 12V to 5V LED power supply project, you’ll need the following components:

1. S2-12V Relay – A 12V relay to control power to the LED circuit.

2. LM7805 Voltage Regulator – A 5V regulator to step down the 12V input to 5V for the LED circuit.

3. Capacitors:

1. C1: 100 µF electrolytic capacitor (input side)

2. C2: 10 µF electrolytic capacitor (output side)

4. Resistors:

1. R1: 220 Ω (current-limiting resistor for the LED)

5. LEDs – A set of standard 5mm LEDs (around 3-5 LEDs depending on your circuit design).

6. 12V Power Supply – A regulated 12V DC power supply or battery pack.

7. Diode (optional) – 1N4007 (for reverse voltage protection)

8. Breadboard or PCB – For assembling the circuit.

9. Jumper wires – To make connections.

10. Multimeter – For testing voltages and verifying connections.

Understanding the S2-12V Relay

The S2-12V relay is a single-pole, double-throw (SPDT) electromagnetic relay that is typically used to control larger currents and voltages with low-power control signals. It is rated for a 12V control signal (which is typical in automotive or 12V-based systems) and can switch currents of up to 10A. In this project, we’ll use the relay to switch the 12V power supply to the LED circuit, allowing the LM7805 voltage regulator to step it down to 5V for the LEDs.

The S2-12V relay has the following key components and pins:

· Coil pins: When energized with 12V, the relay coil creates a magnetic field that moves the internal switch.

· Normally open (NO) pin: This pin is connected to the output (5V circuit) when the relay is activated.

· Normally closed (NC) pin: This pin is connected to the output when the relay is not activated.

· Common (COM) pin: This pin is the central terminal that connects either to the NO or NC pin, depending on the relay state.

Project Design Overview

The goal of this project is to use the S2-12V relay to control the power flow to an LED circuit that needs a stable 5V supply. Here's how we will design the circuit:

1. 12V Power Input: We will provide a 12V input from a battery or regulated power supply to the relay.

2. Relay Control: The S2-12V relay will control whether the 12V power is passed through to the voltage regulator.

3. LM7805 Voltage Regulator: The LM7805 will step down the 12V input to a stable 5V, suitable for driving LEDs.

4. LEDs: The 5V output will power a set of LEDs through current-limiting resistors.

5. Capacitors: Capacitors will filter out any noise and smooth the power supply to the LEDs.

Step-by-Step Circuit Construction

Step 1: Setting Up the Relay Circuit The first component we’ll deal with is the S2-12V relay. Connect the 12V input to the coil pins (pins 1 and 2). When 12V is applied to the coil, the relay will activate and close the NO pin with the COM pin.

1. Pin 1 and Pin 2 (Coil): Connect these pins to the 12V power supply. Pin 2 will go to ground, and Pin 1 will go to the positive terminal of the 12V supply. The relay will activate when this coil is energized.

2. Pin 3 (Common): Connect this pin to the input power (12V) that will be switched on and off by the relay.

3. Pin 4 (Normally Open): This pin will connect to the input of the LM7805 voltage regulator. When the relay is activated, this pin will allow 12V to pass through to the LM7805.

4. Pin 5 (Normally Closed): Leave this pin unused for now, as we’re only interested in switching the 12V to the LM7805 when the relay is triggered.

Step 2: LM7805 Voltage Regulator Setup Next, we’ll connect the LM7805 voltage regulator to the circuit. The LM7805 will step down the 12V input to 5V for the LED circuit.

1. Pin 1 (Input): Connect this pin to the NO pin of the relay (Pin 4). This will supply 12V to the LM7805 when the relay is activated.

2. Pin 2 (Ground): Connect this pin to the ground of the power supply (12V).

3. Pin 3 (Output): Connect this pin to the positive side of your LED circuit (through the current-limiting resistor).

Step 3: Adding Capacitors for Smoothing To ensure smooth operation of the voltage regulator and filter any noise, add capacitors to the input and output of the LM7805.

1. C1 (Input Capacitor): Place a 100 µF electrolytic capacitor across the input and ground pins of the LM7805. This capacitor helps stabilize the input power and reduces noise from the power supply.

2. C2 (Output Capacitor): Place a 10 µF electrolytic capacitor across the output and ground pins of the LM7805 to filter the output voltage and smooth any ripple from the regulator.

Step 4: Connecting the LEDs Now, connect your LEDs to the output of the LM7805. Use a 220 Ω resistor in series with the LEDs to limit the current. Connect the negative terminal of each LED to ground.

1. LED Anode (Positive): Connect this to the output pin (Pin 3) of the LM7805 through the current-limiting resistor.

2. LED Cathode (Negative): Connect this to ground.

You can connect multiple LEDs in parallel if needed, but ensure that each LED has its own current-limiting resistor.

Step 5: Testing and Finalizing the Circuit Once the components are connected, double-check the wiring and connections before powering up the circuit. When the relay is activated (by applying 12V to the coil), the 12V power will pass through to the LM7805, which will step it down to 5V to power the LEDs. You should see the LEDs light up once the relay is triggered.

You can use a multimeter to measure the output voltage at the LED circuit to verify that it is a stable 5V. If the voltage is not correct, check the connections to the LM7805 and the relay.

Troubleshooting

If the circuit isn’t working as expected, here are some things to check:

1. Relay Not Activating: Ensure that the relay is getting the proper 12V signal at the coil. If the relay isn’t switching, try testing it separately to make sure it’s functioning correctly.

2. Incorrect Voltage at Output: Double-check the connections to the LM7805. The LM7805 requires a minimum of 7V at its input, so make sure the input voltage to the LM7805 is sufficiently high (at least 12V).

3. LEDs Not Lighting Up: Check the connections to the LEDs and ensure the current-limiting resistors are properly placed in series with each LED.

Conclusion

In this DIY electronics project, we successfully built a 12V to 5V LED power supply using the S2-12V relay. By using the relay to switch the 12V power to the LM7805 voltage regulator, we were able to provide a stable 5V supply to power a series of LEDs. This project demonstrates how relays can be used to control power flow and how simple voltage regulators can be used to step down