How to use relay without microcontroller [with battery and bulb/LED]

Here’s a simple tutorial for using a relay without a microcontroller, controlling it with a battery and a bulb/LED.

Materials Required:

1. Relay (5V or 12V depending on your battery)
2. Battery (of a voltage matching the relay coil, e.g., 5V or 12V)
3. Bulb/LED (match the voltage of your secondary circuit)
4. Resistor (if using an LED, typically 220Ω for a 5V circuit)
5. Switch or Wire (to control the relay)
6. Connecting Wires

---

Understanding the Relay:

A relay is an electrically operated switch that uses an electromagnetic coil to mechanically control a switch.

• Coil Pins: Two pins to activate the relay (e.g., IN+ and IN- or marked A and B).
• Common (COM): Connected to the load (bulb/LED).
• Normally Open (NO): Circuit is open when the relay is inactive; closes when the relay is activated.
• Normally Closed (NC): Circuit is closed when the relay is inactive; opens when the relay is activated.

---

Wiring Steps for Relay without Microcontroller:

1. Connect the Coil of the Relay

• Relay Coil Pins: Find the two pins connected to the coil. These will activate the relay when powered.
• Connect the positive terminal of the battery to one of the coil pins.
• Connect a switch or simply a wire from the negative terminal of the battery to the other coil pin.
• This forms a circuit for activating the relay.

2. Connect the Load (Bulb/LED)

• Identify the COM and NO (or NC) pins on the relay.
• Connect the positive terminal of the external power supply for the bulb/LED to the COM pin.
• Connect the positive wire of the bulb/LED to the NO pin (if you want it to turn on when the relay is activated).
• For the negative wire of the bulb/LED, connect it back to the negative terminal of the external power source.

3. Test the Relay

• Close the switch or touch the wire to complete the coil circuit. This should activate the relay.
• When the relay is activated, the NO pin connects to COM, turning on the bulb/LED.
• Open the switch to deactivate the relay, which turns the bulb/LED off.

---

Example Diagram:

[Battery (+)] ----> [Relay Coil Pin 1]  
[Battery (-)] ----> [Switch] ----> [Relay Coil Pin 2]  

External Power Source:
[COM] ----> [Positive of Power Source]
[NO] ----> [Bulb/LED Positive]
[Bulb/LED Negative] ----> [Negative of Power Source]

Important Notes:

1. Ensure the relay’s coil voltage matches your battery voltage.
2. If using an LED, add a resistor in series with the LED to prevent it from burning out.
3. Handle the relay carefully if using high-voltage loads.