Usage Notes + Wiring Diagram
- Arduino on USB has 500mW of power
- 8 channel relay appears to take .36W  - or 76mW per coil
- Arduino pins can put that out directly - 200mA for Vcc and GND pin - see Arduino Pin Current Limitations. Otherwise, the multiple output pins are rated for 20 mA, and 40 mA max. Since the signal for the relay can be small, the Vcc and GND connection is sufficient - but not if you want to power more than 3 relays simultaneously.
- See sample direct wiring diagram plus notes on current limits at 
- Sample code to debounce a button press - 
- Start with Pushbutton Without Delay - 
- Or, can start with water relay and 120V for rapid prototyping.