Everything I expected, fast shipping and courteous service. I will be doing business with SainSmart in the furture......

The board feels top notch, quality built. But lacking documentation makes setup tricky.

Ordered 3 boards. Very well built. Tested the boards and relays, everything working great. Will purchase more later for other projects.

Very well built. A little bit expensive, but it is worth.

I have ordered 6 items in your store and they were posted via China Post, It took me 21days before I received my package. It is really a long time, however, the items all I get are just good, they worth waiting.

This relay controller is really worth purchasing, the high quality and reasonable price. Perfect!

When I first looked at this product, I was attracted to its design. After viewing the customer’s reviews, I decided to buy it .Now I received this relay controller and it is absolutely amazing after using it.

This board works well with the Rpi but requires a little thought to implement correctly. First of all the VCC-JD jumper must be removed to isolate the coil voltage from the signal voltage. The logic is backwards from what might be expected. When the Rpi GPIO or port expander pin is "off" (sinking voltage) the relay is energized. The two relay version of this board is easily modified so that when a high is presented, the relay energizes. A trace cut and a couple of jumpers are all that are needed. Other than that, no other considerations are needed. There are some that say that another driver transistor is needed to interface this to the Rpi. This is NOT true. Having said that, there is the advantage that the logic is reversed (GPIO Hi=ON) when a transistor is added. One could add a hex inverter like a 74HC540 and do the same thing. The VCC-JD/VCC jumper must be re moved and +5 volts from a separate power supply be fed to VCC-JD. A wall-wart works nicely and maintains isolation. I recommend that a I2C port expander such as the MPC23107 or MPC23008 be used with this relay board. An SPI bus port expander could also be used (MPC23S17 or MPC23S08) with the Rpi. Utilizing both I2C buses on the RPI, that means that a total of 256 relays can be connected to the Rpi. In addition another 256 relays can be connected via the SPI bus. for a grand total of 512 relays controlled by a single Rpi.

What kind of opto-isolator have you used in this PCB?

I just got the relay. After some test, it works great as expected.