Active low relay board with 5V relays capable of being switched on-off by an opto-isolated digital input. The relays are controlled by a microcontroller connected to the output pin and require a LOW to switch the inputs ON. Suitable for 5V and 3.3V devices, these boards are perfect for Raspberry Pi, Arduino, PIC and various other microcontrollers.
 
16 Channel
Maximum switching voltage: 250VAC / 30VDC
Maximum switching current: 10A
Module operating voltage: 5V
Each relay features an LED indicator
Dimensions: 37 x 26 x 18mm (Length x Width x Height)
Opto coupler PC817 one each used for Inputs and also 2 nos Relay drive IC  ULN2803 to drive 16 channels.
Always use external power source 5v for the relay board and make Gnd common for both Microcontroller and power source.