Features: Compatible with Arduino/Seeeduino. Standardized shape design. Working status indicators for each relay. High quality relays. Provides NO/NC interfaces. Specifications: Voltage: 4.75 ~ 5.25VDC (Typical: 5VCD) Current: 8 ~ 250mA Switching voltage: 35VDC Switching current: 8A Frequency: 1HZ Switching power: 70W Relay life: 100,000 Cycle ESD contact discharge: ±4 KV ESD air discharge: ±8 Product size: Approx. 6.9 * 5.4 * 3.1in / 2.7 * 2.1 * 1.2in Product weight: Approx. 65g / 2.3in Package size: Approx. 10.6 * 7 * 3cm / 4.2 * 2.8 * 1.2in Package weight: Approx. 82g / 2.89oz Cautions: Place 2 layers of electrical tape on the top of the Arduino's usb connector. This will prevent the relay shield from making contact. Do not operate voltage more than 35V DC. Interface function: J1 Interface: COM1- Common pin NC1- Normally Closed. Will be connected with COM1 when RELAY1 pin is set low and disconnected when RELAY1 is high; NO1- Normally Open. Will be connected with COM1 when RELAY 1 pin is set high and disconnected when RELAY1 is low; J2-4 Interfaces are similar to J1 interface, except that the control ports are RELAY2-RELAY4. 4 Digital Pins to control 4 Relays: RELAY1-RELAY4 pins could be connected directly with Arduino pin number of 7-4, so that four relays could be easily controlled by the Arduino.