I am using an Arduino Mega connected to the WiFi with your Cytron WiFi shield. I have a lot of temperature sensors and relay modules connected to the Arduino to do load shedding control during peak electricity rates in Southern California.
The system is connected to a small Minix brick computer so I can manage it remotely using Google Chrome Remote Desktop.
Because I run out of power I installed and external 9VDC regulated power supply. Whenever I plug in the 9VDC the 5VDC on the Arduino drops from 4.9V to 4.4 volts and when all the relays are activated the voltage drops to 3.5 VDC. When I unplug the 9VDC and only leave the USB from the Minix plugged in the voltage goes up to 3.7 volts.
On a second system I have an identical setup using an Ethernet card the voltage stays at 5VDC on the Arduino bus with 9VDC plugged in.
Is there an issue with the shield to cause this voltage drop? I checked everything but cannot get to an answer here.
Herman