I'm on a project in which a number of 5V relays are used. Since I have an LCD connected directly on top of my Mega2560 (via LCD TFT Shield) and it draws significant current from the built-in 5V regulator on the board, as I connect the relay board VCC and GND to the arduino, suddenly LCD brightness decreases and it goes black. So I decided to use a computer power supply (PSU) in order to power the relays externally. I also connected the GND of PSU to that of arduino. However, the LEDs on the relay board are always half bright, i.e. regardless of the ON or OFF command from arduino. This is while when I disconnect the LCD, and connect the relays directly to the arduino board, everything works fine. Does anyone know what the problem refers to, and if I can do anything about it?
The connections are as follows:
Mega GND is connected to PSU GND (black wire)
Relay board VCC is connected to PSU +5V (red wire)
Relay board GND is connected to PSU GND
Relay board data (IN1 to IN8) are connnected to Mega digital I/O pins