When I finally got around to playing with the hardware, I used (or should I say tried to use) Seeed Studio's Wiki Page for the board (https://wiki.seeed.cc/Raspberry_Pi_Relay_Board_v1.0/) to guide my efforts. Unfortunately, I quickly learned that the article was incomplete and didn't have everything I needed to work with the board. I mounted the board on my Raspberry Pi, powered it up, ran their sample test application, and got nowhere. It simply didn't work.
I sent Seeed Studios an email asking for help and posted a couple of questions on their community forums, but had to wait more than a month to get a response. When I finally did hear back, it was to let me know that they were on vacation and it would be an even longer wait for help. Sigh. Finally, they contacted me and offered to help.
After another week of sending them screen shots, I finally got useful information and was able to get the board operational. The purpose of this article (and associated Github repository at https://github.com/johnwargo/Seed-Studio-Relay-Board) is to show you how to use the board so you'll avoid the issues I had.
Update: After publishing this article, I shared this information with the folks at Seeed Studio. They then updated their Wiki article with information directly copied from this article and the associated GitHub repository readme file. So, you'll finally find good, useful information on their product Wiki page - because I wrote it.
In the Github repository, I shared the code Seeed provides to test the board (so that you can grab it using git rather than copying and pasting it from a Wiki page) plus a Python module (and associated test application) you can leverage to use the relay board in your own Raspberry Pi projects. I also created a complete Raspberry Pi relay controller application (using Python and Flask); I'll publish information about that soon.
The steps for installing the board and verifying that it works includes the following steps:
Mount the Relay board on the Raspberry Pi
Enable the Raspbian I2C software interface
Validate that the Raspberry Pi recognizes the board
Run some Python code to exercise the board
In the rest of this article, I'll show you how to do all of those things.
Mounting the Relay Board
Mounting the board is easy, it comes with the appropriate female headers you need to mount it on any Raspberry Pi board with male headers. Note: You'll have to add male headers to the Raspberry Pi Zero to use the board.
Seeed Studio recommends putting some electrical tape on top of the Raspberry Pi Ethernet port before mounting the board. If you mount the board without using standoffs (as I've done in the example figure below), there's a chance the board will make contact with the Ethernet port housing and cause a problem.