If the jumper is installed, the relay activates when IN = LOW. The wiring is identical, but logic is reversed.
Introduction In the world of electronics and microcontroller projects (Arduino, Raspberry Pi, ESP8266, STM32), the ability to control high-power devices—such as lamps, motors, solenoids, and pumps—using low-power logic signals is essential. The YL105 is one of the most popular and widely available single-channel relay modules designed precisely for this purpose. yl105 datasheet
int relayPin = 7; void setup() pinMode(relayPin, OUTPUT); digitalWrite(relayPin, LOW); // relay off initially If the jumper is installed, the relay activates