The relay shield utilizes four high quality relays and provides NO/NC interfaces that control the load of high current, which means it could be a nice solution for controlling devices that couldn't be directly controlled by Arduinos Digital I/Os. Standardized shield form factor enables smoothly connection with the Arduino. The shield also has four dynamic indicators show the on/off state of each relay. Note: Headers of this product is shipped unsoldered. Cautions: Place 2 layers of electrical tape on the top of theArduino's usb connector. This will prevent the relay shield from making contact. Do not operate voltage more than 35V DC.