How to Use MKR Relay Shield: Examples, Pinouts, and Specs

The MKR Relay Shield (Manufacturer Part ID: TSX00003) is an add-on board designed for use with Arduino MKR series boards. It enables users to control high-voltage devices such as appliances, lights, and other electronic equipment. The shield features two independent relays, allowing for safe and efficient switching of devices that operate at higher voltages and currents than typical microcontroller outputs can handle.

• Home automation systems (e.g., controlling lights, fans, or appliances)
• Industrial automation and control
• IoT projects requiring high-voltage device control
• Prototyping and testing of relay-based circuits

The MKR Relay Shield is designed to interface seamlessly with Arduino MKR boards. Below are its key technical details:

The MKR Relay Shield connects directly to the Arduino MKR board via its headers. Below is the pin configuration for the relay terminals:

1. Attach the Shield: Plug the MKR Relay Shield directly onto the Arduino MKR board. Ensure the headers are aligned properly.
2. Connect the Load:
   • For each relay, connect the load to the NO (Normally Open) terminal and the power source to the COM (Common) terminal.
   • If you want the load to be powered when the relay is off, use the NC (Normally Closed) terminal instead of NO.
3. Power the System: Power the Arduino MKR board via USB or an external power source. The shield will draw power from the MKR board.
4. Control the Relays: Use digital pins D1 and D2 on the MKR board to control Relay 1 and Relay 2, respectively.

• Voltage and Current Ratings: Do not exceed the maximum switching voltage (220V AC / 30V DC) or current (2A) for each relay.
• Isolation: Ensure proper isolation between the high-voltage side (relay terminals) and the low-voltage side (Arduino MKR board) to avoid damage or hazards.
• External Power: If controlling high-power devices, consider using an external power source for the load to avoid overloading the Arduino board.
• Code Logic: Use appropriate delay intervals in your code to prevent rapid switching of the relays, which can cause wear and tear.

Below is an example sketch to control the relays using an Arduino MKR board:

// Example code to control the MKR Relay Shield
// Relay 1 is connected to pin D1, and Relay 2 is connected to pin D2.

#define RELAY1_PIN 1  // Digital pin for Relay 1
#define RELAY2_PIN 2  // Digital pin for Relay 2

void setup() {
  // Initialize relay pins as outputs
  pinMode(RELAY1_PIN, OUTPUT);
  pinMode(RELAY2_PIN, OUTPUT);

  // Start with both relays off
  digitalWrite(RELAY1_PIN, LOW);
  digitalWrite(RELAY2_PIN, LOW);
}

void loop() {
  // Turn on Relay 1
  digitalWrite(RELAY1_PIN, HIGH);
  delay(2000); // Keep Relay 1 on for 2 seconds

  // Turn off Relay 1 and turn on Relay 2
  digitalWrite(RELAY1_PIN, LOW);
  digitalWrite(RELAY2_PIN, HIGH);
  delay(2000); // Keep Relay 2 on for 2 seconds

  // Turn off both relays
  digitalWrite(RELAY2_PIN, LOW);
  delay(2000); // Wait for 2 seconds before repeating
}

1. Relays Not Switching

   • Cause: Incorrect wiring or insufficient power supply.
   • Solution: Double-check the wiring of the load and ensure the Arduino MKR board is powered properly.

2. Arduino Board Resets When Relays Switch

   • Cause: High inrush current from the load.
   • Solution: Use a separate power supply for the load or add a flyback diode across the relay terminals.

3. Relays Stuck in One State

   • Cause: Faulty relay or incorrect control signal.
   • Solution: Verify the control signals from the Arduino board and test the relay with a multimeter.

4. Load Not Turning On/Off

   • Cause: Incorrect connection to the relay terminals.
   • Solution: Ensure the load is connected to the correct terminals (NO, NC, and COM) based on the desired behavior.

Q: Can I use the MKR Relay Shield with non-MKR Arduino boards?
A: The shield is specifically designed for MKR boards. While it may be possible to adapt it for other boards, it is not recommended due to pin alignment and power compatibility issues.

Q: Is the MKR Relay Shield suitable for controlling motors?
A: The shield can control small motors within the 2A current limit. For larger motors, use a motor driver or an external relay module.

Q: Can I stack other shields on top of the MKR Relay Shield?
A: Stacking is possible, but ensure the additional shield does not interfere with the relay terminals or exceed the power capacity of the MKR board.

Q: How do I know if a relay is active?
A: The MKR Relay Shield includes onboard LEDs that light up when a relay is activated.