SainSmart16-Channel 12V Relay Module Board for Arduino DSP AVR PIC ARM

No issues with any boards I received, I have more than 5 running various aspects of my smart home for more than 2 years.For those that need help this is the easiest way to connect them to the Raspberry PI:The relays are triggered on when the pin of the relay is pulled LOW (0) volts. the pins are made for an Arduino but will work with the PI if you connect a 3V LED between the relay board and the PIGND pin on relay board ----------> GND pin on Raspberry PIRelay Board Pin------> LED Anode (Long Wire) / LED Cathode (Short Wire) -------> GPIO of Raspberry PIyou will have to do this 16 times.This has the added benefits of;Indicator if relay is supposed to be on to mount in project box side/top (Unused just leave inside)Relays do not trigger ON when rebooting the PIRelays do not trigger ON when PI is offall parts are cheap and comparable with using resistors.How this works:When the LED is used this way it is essentially a device that drops the voltage by 3V. converting any excess power to light. The PI requires 3.3v maximum to its pins. This method reduces the 5v to 2v for the PI. (You can check with a multi-meter)When the PI GPIO is HIGH (ON) there is 3.3v at the PI and 5v at the relay board. Because the LED requires 3v to operate and there is only 1.7v the led does not conduct power and the opto-coupler in the relay board stays deactivated.When the PI GPIO is LOW (off) there is 0v at the PI and 2v at the relay board. Because the PI is forcing the pin low the LED begins to conduct, turning on, The current limiting resistors in the relay board keep the LED from conducting too much power (and burning out) and still provides enough to activate the opto-coupler causing the relay to activate.

Ok, I admit it, it took me way too long to figure out how to hook this thing up. In case anyone else is looking at this and wondering how it works, here's how it gets hooked up:1) The header pins on the bottom of the main picture get wired directly to the Arduino board. Connect one of the 5v pins to a 5v header on your Arduino and connect one of the Gnd pins to a ground header on the Arduino. Each one of the relays has a corrosponding header down there, too, which get connected to a digital output on your Arduino. You can run each wire individually or run over a ribbon cable to a project board and break it out from there. Either way, getting the header pins hooked up allows the logic to fire, and makes the lights work so you can at least diagnose/debug your program.2) Next, the relay board needs a 12v dc input wired up to the blue terminals on the bottom. These are wired to the relays, which make the relays actually fire. The voltage magnetically pulls a piece of metal away from one pole to the other. This action makes a noticeable clicking noise, which is a little annoying, but also lets you know it's working.3) Each relay has 3 terminals located along the sides. One side is normally opened, the other is normally closed. Use this to either make or break the circuit that you have wired up for your lights, motors, or whatever else is involved in your project that draws more than 5v or needs to be kept isolated from the Arduino board.So yeah, keep in mind that you'll need a 12v power source to actually make the relays fire. All in all, it's a very well put together board, and would make a great control hub for something like say... a model train set or robot.

It works well, QC issues notwithstanding. But you bought it because it's cheap, so we can live with the QC, right?It is a bit strange that a relay becomes active when the input goes low at the pin, but because the relays can be normally open or normally closed (depending on which screw terminal you use) then the relay can pass current when your input is high...it's just that the LED will go on when your input is low...which is weird. BUT it is useful, because then you can set up your relay to be idle (non energized) for high duty-cycle applications.One review states that the optocouplers aren't actually being used properly, but because one 5V source comes from your Microcontroller (RPi, Arduino, etc) and the other 5V source comes from the regulated power supply from the board, the relays and analog switch ICs *are* actually optically decoupled from the signal source. It's easy to confuse this on the schematic and board layout because they are both labeled "5V."It's just an odd bit of logic, but it makes sense when you consider that not all low-voltage controller sources are capable of delivering a 5V *signal* (many are 3.3V) to drive the optocoupler source...but most controller sources DO HAVE a regulated 5V output to drive the optocoupler when the IO pin goes low, and drains to ground through its pull-down.Because the LEDs are driven by the 12v side of the circuit, I'm sure it could be modified to light when the circuit is NOT ENERGIZED, but it's really a minor detail...you can still connect your individual components according to duty-cycle per relay, and if you have enough voltage overhead, simply drive a light with the source-load circuit.I used mine to run a small solenoid and motor orchestra, controlled by a Teensy with the Arduino Midi Library installed. Additionally, I glued some tuning forks to the relays themselves, and the tones ring out as the solenoid fires, in addition to striking another instrument, resulting is some interesting additional harmonies. The 12V power supply I used powers both the relay board *and* the source for the solenoids and motors. The power consumption of the relay board with ALL relays ENERGIZED comes to 555 mA, but by strategically connecting my loads, if all 13 notes and 3 motors run at once, it peaks at 450 mA...thus I run the whole shebang on a 12V 1A power supply, with the Teensy isolated and protected from the other currents.I only wish that the SainSmart was a bit smaller...I feel like you could do this for a 12V circuit with only optocouplers. But it's cool that you *could* switch AC with this, if you chose.4 stars because there is no descriptive documentation. I'd give it 4.5 because there ARE schematics and pcb layouts on the sainsmart website.