Review on SainSmart 101 70 103 16 Channel Relay Module by David Stewart

Works well despite quality control issues. But you bought it because it's cheap, so we can live with QC, right? It's a little strange that the relay gets active when the input on the pin goes low, but since relays can be normally open or normally closed (depending on which screw terminal you use), the relay can conduct current when your input is high . Only the LED will light up when your input is low. which is strange. BUT this is useful as you can then put your relay in open circuit (no power) for high load applications. (RPi, Arduino, etc.) and the other 5V source comes from a regulated power supply on board, the relays and analog switching ICs are effectively optically decoupled from the signal source. It's easy to confuse this on the schematic and breadboard as both are marked "5V". signal* (many of them 3.3V) to drive the optocoupler source. However, most controller sources have a regulated 5V output to drive an optocoupler when the IO pin goes low, and is drained by pulling it down to ground. Since the LEDs are driven from the 12V side of the circuit, I'm sure they can be modified to light up when the circuit is NOT FOUND, but that's really a minor detail. If you have enough overhead, simply control the light with a source-load circuit. I used mine to run a small orchestra of solenoids and motors controlled by Teensy with the Arduino Midi library installed. Also, I glued some tuning forks to the relays themselves and when the solenoid was actuated there was noise, in addition to the beating of the other instrument, resulting in some interesting additional harmonies. The 12V power supply I used powers both the relay board* and the source* for the solenoids and motors. The current draw of the relay board with ALL relays activated reaches 555mA, but with my strategically connected loads the peak reaches 450mA with all 13 notes and 3 motors running at the same time. Power supply, with Teensy, isolated and protected from other currents. I just wish SainSmart was a little smaller. I have a feeling you could do this for a 12V circuit using just optocouplers. But the cool thing is that you can use it to switch AC if you want. 4 stars because there is no meaningful documentation. I would give it a 4.5 because the sainsmart website has schematics and PCB layouts.