SPECIFICATION

• 8 channel 2 AMP Solid State Relay board Good for lighting- holiday displays etc
• The input control signal voltage: (0-0.5V LOW solid state relay OFF) (2.5-20V high solid state relays ON)
• Rated output load: 2A at 100 to 240VAC (50/60Hz)
• Load voltage range: 75 to 264VAC (50/60Hz)
• Load current: 0. 1 to 2 AMP
• Power supply: 5VDC / 160mA (all channel ON)
• Load type: General purpose
• Isolation: Phototriac
• Zero cross: Yes 

Use it to control various appliances, and other equipments with large current.
It can be controlled directly by Microcontroller (Arduino , 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic).
 
Product Dimensions: 155 x 55 x 24 mm

USE:

Very easy to use with an Arduino. Just needs 2 wires for GND + 3.3V and 8 wires for the 8 relays. You can use the newer arduinos that are in 3.3 V logic or a Raspberry Pi GPIO (also in 3.3 V logic) or any of the older Arduino (Uno, Mega) which are 5V.
The outputs relays are silent -- search "OMCRON G3MB-202P" for the datasheet.

These are zero-crossing PhotoTRIACs with snubber circuits. Their load rating is up to 2 A at 100-250 VAC.
Works fine with low-voltage 16 VAC too, for example model train accessories power supply.

[Edit] To clarify one thing: the solid state relays use triacs (TRIAC=triode for alternating current) which means the relays will only close when using an AC load. You cannot drive a DC load with these. If you like a schema to understand things, consider this:

[arduino] ---[3.3V or 5V DC]---> [SainSmart SSR] <---[AC]---> [Circuit to be controlled]

The outputs per relay only have 2 screws for an NO connection.
If you need an application with NO/NC or if you need to drive a DC load, you may want to try the 5 V SainSmart 8-Channel Relay Module.

Module interface:
Input section:

• DC +: positive power supply (by relay voltage power supply)
• DC-: connect power negative
• CH1: 1 relay module signal to trigger the end (high level trigger effective)
• CH2: 2-channel relay module signal to trigger the end (high level trigger effective)
• CH3: 3 relay module signal to trigger the end (high level trigger effective)
• CH4: 4-channel relay module signal to trigger the end (high level trigger effective)
• CH5: 5 relay module signal to trigger the end (high level trigger effective)
• CH6: 6-channel relay module signal to trigger the end (high level trigger effective)
• CH7: 7 relay module signal to trigger the end (high level trigger effective)
• CH8: 8-channel relay module signal to trigger the end (high level trigger effective)