I have a RPi2 to which is connected a 4 channel relay board and a LDR sensor module. The connections are as follows:
Relay Board VCC => Pin #2 (5V)
Relay Board Ground => Pin #6 (Ground)
Relay Board Input1 => Pin #11 (GPIO17)
LDR Sensor VCC => Pin #4 (5V)
LDR Sensor Ground => Pin #14 (Ground)
LDR Sensor Data => Pin #13 (GPIO27)
A python script monitors the LDR sensor and depending upon that the Relay is turned ON or OFF.
The problem is that when the relay is switched ON, the Red LED on the Pi starts blinking. I have tried various USB adapters rated 5V 2A and 5.1V 2.1A, but the problem persists. The relay is working fine but I am worried about the blinking LED.