SainSmart 16-Channel 12V Relay Module Board for Arduino DSP AVR PIC ARM

The Sainsmart 16 Relay board is an inexpensive bargain. The primary purpose is to isolate the computer from the outputs. RFI or spikes can travel down a wire into a computer and mess up the logic causing any output to go on randomly. This board provides isolation in the relays, the standard usually being 1500 volts and opto isolation on the inputs using an optoisolator diode and optical transistor driving an amplifier.The board is wired when the ground is connected between the computer and the relay board. This is the only power connection needed along with the 16 discreet inputs which operate the relay with a ground input to one of the 16 pins on the header of the board.The 5volt pins 19 and 20 are sufficient to provide power for the computer but the real purpose is to provide input power to run the opto-isolators. Apparently this board has been provided with either 5volt or 12 volt relays. You should check the relay marking before connecting power on the power input pins. The Relays are SPST non-connected contact types, so you may wire virtually any load, but beware that the PC board and the associated connectors will probably not really handle much more than an amp at up to 120vac or 36vdc even though the relay is rated at a higher loads for its contacts. A good input source is Elegoo Mega pins 22 to 55 or a string of 74HC595 serial shift registers. If you connect two relay boards, you will probably need to breakout the wires to prevent connecting a solid 5vdc source to an input pin on the Mega. Note that the Mega has a female socket and the relay board has a male socket. Twenty wire Multicolor flat cable with connectors is a good choice for wiring.Also note that the inputs support open collector inputs which permit wired "OR" wiring. Personally, I would not use the 5vdc pins for anything other than the relay board. For safety operation I would provide +12Vdc at about 0.8Amps or more. I use this board to power 16 slow motion Tortoise switch machines on my Model Railroad using a +12vdc and a +24vdc power source. You really don't need a schematic since the relay board is so redundant in its wiring. The 5 volt converter is a LM2576 12v to 5v 3 amp converter.

I'm using this board to power an electronic sign. The relay will control various lights to create an animation.First things first, there is no documentation included with the board; so, you're probably going to need to go to secondary sources like youtube (https://www.youtube.com/watch?v=CSs-he1Mk3k) to understand how the board functions. It's functionally simple, though. It requires a 12V 1.0A power supply to power the relay array.I used it with an Arduino Mega 2560 R3 board. Connect from Arduino GND to the Relay GND pin. Connect one or more output pins from the Arduino to the input pins on the Relay input pins. The voltage flowing from the Arduino to the Relay completes the circuit by flowing back to GND on the Arduino. You CAN connect the 5V pin on the Relay back to the Arduino 5V power if you want the relay's 12V -> 5V to power the Arduino. This is nice because you don't have to supply separate power to the Arduino but not required.You can test the Relay board easily. Plug in 12V power supply. Connect a wire from GND to any of the input pins. You should see the light next to the corresponding relay switch turn ON and hear an audible click. That will tell you right out of the box whether the relays are functional without having to connect an Arduino. I did not test the Relay board with a Raspberry Pi; however, I would imagine that as long as the power supply and the voltage from the pins are stable, everything *should* work fine. This device doesn't care who powers or controls it.There is one thing that you should be aware of. Since these are essentially mechanical switches controlled by electricity, there is an audible click when you flip a relay ON or OFF. If you've got these things turning ON and OFF repeatedly, they will chatter away pretty noisily. This isn't a problem for me because my installation is in a sign located (temporarily) outdoors; however, if you're planning on using it indoors, be aware of the noise. You might want to use a different technique (transistor, etc).