About high level and low level-triggered mode:

1. High-level trigger refers to the signal voltage between input and trigger, can be understood as a signal input with VCC cathode short-circuit triggered a way;
2. Low-level trigger refers to the signal voltage between the input terminal and Earth OV trigger, can be understood as the signal input terminal and the GND negative electrode short circuit triggered away  1-channel relay module connection

Jumper Instruction = The relay can be turned on when we connect 5v to one end and the other to -5v / Gnd, while talking about the jumper, if we short the VCC and the middle pin, then our relay will act as high level-triggered relay means that when we will apply + 5V input on its input pin it will be turned on and when the jumper will be set to “middle and GND”, it will act as a low-level triggered relay, It means that relay will be triggered when we implement the 5V / GND on its input pin.

Features :

1. 2 LEDs to indicate when relays are ON.
2. Works with logic level signals from 3.3V or 5V devices
3. Opto isolation circuitry
4. Module with diode current protection, short response time
5. Around the board with 4 mounting holes, hole diameter 3. 1 mm, easy installation and fixing