Review on Lystin 4 Channel Relay Module Control Board for UNO R3 MEGA 2560 1280 DSP ARM PIC AVR TTL Logic STM32 Raspberry Pi - DC 5V DC 230V with Optocoupler by Paul Green

Note that when using this device you have to give a LOW signal from your microprocessor to turn on the relay. Outputting a HIGH signal from your microcontroller turns the relay off. Your output pin connected to the relay's control input should be able to draw 13 milliamps. Note that turning on all eight relays may cause your microcontroller to draw more current than it can safely handle. Check your specs. Since the voltage drop is very small, the reduction in current does not usually cause large power dissipation (heating). this is usually the culprit behind such device overload situations. However, to be on the safe side, check how high the maximum simultaneous output current consumption is.