So I am currently working on a project as part of my Uni assignment that uses 3 DC motors and 2 Servo Motors, I currently have a servo and a DC motor connected to my Arduino Uno - l293d motor shield. The DC motor is routed through a PCB which I have manufactured which includes uses MOSFET. I have also opted to power my servo motors with 4 AA Alkaline Batteries so that I can connect the other 2 DC motors from the shield.
My issue is that whenever I send power to my PCB, the Servo motor is affected by it; in that the position of the servo changes while the DC motor is powered. I have also discovered that it is the ground pin of the servo which is being affected and not the S pin, which on the shield is pin 9. I have tried changing the ground pin to every spot on the board to no avail.
Does anyone know what the specific issue is and how I can go about solving it?
If a schematic of the PCB is required, I can provide one. I am just cautious about uploading Uni content online. My l293d motor shield was purchased from my local Jaycar (Australian Electronics Store)