SainSmart's website also has a file that looks like the PCB layout.
Here's an image of the control electronics part.
Based on this info, I would *NOT* recommend use with Teensy LC. The board has a 5V power supply and the inputs go to the optocoupler diodes and then resistor right to the 5V power.
Teensy LC is not 5V tolerant. Using it with this board will risk damage to the hardware!
Also, this relay board optocoupler section seems to be a rather stupid design. I can't imagine what Sainsmart's engineers were thinking. Well, actually I can imagine... very likely an arbitrary requirement to have optocouplers (probably copying the specs of some well designed relay product) and their engineers were either lazy, incompetent, or just didn't care.
The way they designed this board, the optocouplers don't actually isolate you from anything, other than isolation already provided by the relays. The optocouplers are truly redundant, serving no useful purpose. Well, no purpose other than to sell the board to people who can't tell the difference and believe the optocouplers must be adding some value. They aren't. The optocoupler inputs are all connected by resistors to the 5V, which shares GND with the 12V power - so you are indeed galvanicly coupled to the 12V power supply despite the fact this board has 16 (useless) optocouplers!
I would not recommend buying this Smartsain product. Its design is just terrible.
If you do get it, use Teensy 3.2 or 3.5 (which are 5V tolerant), or Teensy 2.0 (which runs on 5V). For use with Teensy 3.2 or 3.5, to control these relays you would connect GND from the relay board to Teensy's GND, and connect digital pins to the inputs. To control the relay, you would do something that may seem strange. To turn the relay on, you'd use pinMode(pin, OUTPUT) and digitalWrite(pin, LOW). To turn the relay off, you would use pinMode(pin, INPUT). Changing to input mode is needed, because Teensy 3.2 & 3.5 have 3.3V outputs. You can't drive the pin to 5V. But if you just put the pin into INPUT mode, it will stop driving the optocoupler and the relay will turn off.
I'm pretty sure that will make this relay board work. But only try that on Teensy 3.2 or 3.5. Do not use Teensy LC or Teensy 3.6, because they are not 5V tolerant.
If you haven't purchased this relay board yet, I would advise against wasting your money. Get a better one. If it has optocouplers, get one where the engineers who designed the board were smart enough (or copied a design from a competent engineer) where the optocouplers really do give you a second layer of protection. This Smartsain 16-Channel 12V Relay Module is at best a shoddy product designed by people who either didn't understand optocouplers or just didn't care.