Review on 🔌 ICStation Relay Power Switch Module with Optocoupler - 2PCS | High-Level Trigger | DC 3V 3.3V | For ESP8266 Development Board Arduino by Mark Loredo

It seems to me that the reviews contain a decent amount of incomplete information that can be misleading. They are sold as 3V, but the 3V logic signal is barely enough to trigger the optocoupler. 3 times 3 is much more reliable. In addition, the input current is very dependent on the voltage. - At 3V I've found that the relay is normally energized and the input pin draws about 1mA (below this the relay doesn't always switch). - On 3x3 the relay was very reliable and the input contact drew about 2.8mA. - At 5V the relay was still very reliable and the input pin drew about 17mA. - Placing a 1kΩ resistor in series with the 5V input reduced the input current to 1.8mA, which was enough to trip the switch. Essentially what happens here is that the input pin directly feeds the optocoupler's internal LED along with a status indicator with a small current limiting resistor. The internal LED requires a minimal amount of current to "turn on" and the output is then boosted by a transistor on the output side. Maybe do a little test to see what kind of resistor you need to sink the input current to 2mA and you can use whatever voltage you want. I removed the star for two reasons. The jumpers for isolating/powering the coil are not individually labeled, and the coil itself draws more current than other relays I've used. At 3V it will draw 100mA, at 3v3 it will draw 115mA and at 5V it will draw 160mA. Also, a better design would use a transistor on the input to stabilize (and reduce) the input current and also make the input active low instead of active high.