How to Use WeMos D1 Mini Relay Shield: Examples, Pinouts, and Specs

The WeMos D1 Mini Relay Shield is a compact and versatile add-on designed specifically for the WeMos D1 Mini development board. It allows users to control high-voltage devices (such as lights, fans, or appliances) using low-voltage signals from the D1 Mini. This shield is ideal for IoT applications, home automation, and remote control systems. Its small form factor and ease of use make it a popular choice for hobbyists and professionals alike.

• Home automation (e.g., controlling lights, fans, or appliances)
• IoT projects requiring high-voltage device control
• Remote control systems
• Industrial automation and monitoring
• Smart energy management systems

The WeMos D1 Mini Relay Shield is designed to work seamlessly with the D1 Mini and features the following specifications:

• Operating Voltage: 5V DC (powered via the D1 Mini)
• Relay Control Voltage: 3.3V (compatible with D1 Mini GPIO pins)
• Relay Output Ratings:
  • Maximum Voltage: 250V AC or 30V DC
  • Maximum Current: 10A
• Relay Type: SPDT (Single Pole Double Throw)
• Dimensions: Matches the D1 Mini form factor
• LED Indicators: Onboard LED to indicate relay status
• Weight: Approximately 5g

The WeMos D1 Mini Relay Shield connects directly to the D1 Mini via its pin headers. Below is the pin configuration:

1. Attach the Shield: Plug the WeMos D1 Mini Relay Shield directly onto the D1 Mini board. Ensure the pins are aligned correctly.
2. Connect the Load:
   • Identify the relay's three terminals: COM (Common), NO (Normally Open), and NC (Normally Closed).
   • Connect the high-voltage device (e.g., a light or fan) to the COM and NO terminals if you want the device to turn on when the relay is activated.
   • Use the COM and NC terminals if you want the device to turn off when the relay is activated.
3. Power the System: Supply power to the D1 Mini via USB or an external power source.
4. Control the Relay: Use the D1 Mini's GPIO pin (default: D1) to send a HIGH or LOW signal to control the relay.

• Safety First: Always ensure the high-voltage side of the relay is properly insulated to prevent electric shock or short circuits.
• Current Limits: Do not exceed the relay's maximum current and voltage ratings (10A, 250V AC or 30V DC).
• External Power: If controlling multiple relays or high-power devices, consider using an external power supply to avoid overloading the D1 Mini.
• GPIO Pin Selection: By default, the relay is controlled via GPIO pin D1. If you need to use a different pin, modify the code accordingly.

Below is an example code snippet to control the relay shield using the D1 Mini:

// Example code to control the WeMos D1 Mini Relay Shield
// This code toggles the relay ON and OFF every 2 seconds

#define RELAY_PIN D1  // Define the GPIO pin connected to the relay

void setup() {
  pinMode(RELAY_PIN, OUTPUT);  // Set the relay pin as an output
  digitalWrite(RELAY_PIN, LOW);  // Initialize the relay to OFF state
}

void loop() {
  digitalWrite(RELAY_PIN, HIGH);  // Turn the relay ON
  delay(2000);  // Wait for 2 seconds
  digitalWrite(RELAY_PIN, LOW);   // Turn the relay OFF
  delay(2000);  // Wait for 2 seconds
}

1. Relay Not Activating:

   • Cause: Incorrect GPIO pin configuration or wiring.
   • Solution: Verify that the correct GPIO pin is defined in the code and connected to the relay.

2. High-Voltage Device Not Working:

   • Cause: Incorrect wiring of the high-voltage side.
   • Solution: Double-check the connections to the COM, NO, and NC terminals.

3. Relay Clicking but No Output:

   • Cause: Insufficient power supply or damaged relay.
   • Solution: Ensure the D1 Mini is receiving adequate power. Replace the relay shield if necessary.

4. Overheating:

   • Cause: Exceeding the relay's current or voltage ratings.
   • Solution: Ensure the load does not exceed 10A or 250V AC/30V DC.

• Use a multimeter to check the continuity of the relay terminals when activated.
• Test the relay with a simple LED circuit before connecting high-voltage devices.
• If the onboard LED does not light up when the relay is activated, check the power supply and GPIO signal.

By following this documentation, you can effectively integrate the WeMos D1 Mini Relay Shield into your projects and troubleshoot any issues that arise.