Servos + Arduino on same power supply = flickering... HELP!!

Hi all,

I hope you’re having a great day. I’m working on a desktop wave tank and am running into a problem when trying to power the Arduino and servos from the same power supply. I’m using a 12v 5a power supply and running it through a 5a buck converter to feed 6.6 volts into the two servos https://www.amazon.com/DS3218-Digital-Servo-Torque-Waterproof/dp/B07TKTQ2NZ. When I power the servos from the buck converter and Arduino from my computer, all is fine. But, when I connect the Arduino Vin to the 12-volt power supply as well, the Arduino LEDs and the attached LCD screen begin to flicker. I’ve attached my schematic and an image below. I’ve linked a video of normal operation with the laptop power supply and of the flickering.

The servos don’t have a load when this flickering is happening so I have a hard time believing I’m drawing too much current from the power supply. Perhaps the servos are adding lots of noise or causing voltage spikes? I’d love to know what you guys think is going on.

How can I rewire the circuit or add components so that both the servos and Arduino are powered by the 12volt power supply? Thanks so much for your comments. They are much appreciated!

Flickering video:

Regular operation video:

Before you start tossing solutions to your problem, measure the voltages before and during the flickering problem and report back the results.

Paul

When Arduino + Servos run from 12v 5a power supply

Power supply output - 12.31v

Buck converter output 6.70v

Arduino 5v output - fluctuating between 3.56-3.65v

Arduino powered by laptop + Servo from 12v 5a supply

Power supply output - 12.30v

Buck converter output - 6.70v

Arduino 5v output - 5.12v

Schematic sure looks ok. Have you tried removing the power from the servos and leaving the 12 volts to the Arduino?

Paul

From those numbers it looks like you're overloading the Arduino internal regulator when it's running on 12.3V.

Just for a test can you try running the 6.7V to the Arduino Vin instead of the 12.3V? 6.7V is a little on the low side but at least the regulator won't overheat so easily.

Steve

Thanks for the reply. When I connect the Arduino to the 6.7 volt output via the VIN pin, the Arduino LEDs faintly light up and the LCD doesn't turn on. I'm measuring the Arduino 5V voltage that feeds into the LCD as 2.16 volts.

Paul_KD7HB:
Schematic sure looks ok. Have you tried removing the power from the servos and leaving the 12 volts to the Arduino?

Paul

When I connect the 12v supply to the Arduino VIN pin (with the buck converter and servos disconnected) the Arduino turns on with bright LEDs. The LCD backlight is on but the screen is not displaying the text it should show. The Arduino is outputting 3.10 volts from the 5v output.

So 12.3V in = 3.6V out. 6.7V in = 2.2V out. We are talking about a Nano? So there's only the regulator between Vin and 5V out. But I can't remember a regulator behaving like that. They usually just die.

Beats me. At this point I'd probably disconnect everything from Vin and try feeding 5V from some other source direct to the 5V pin.

Steve

slipstick:
So 12.3V in = 3.6V out. 6.7V in = 2.2V out. We are talking about a Nano? So there’s only the regulator between Vin and 5V out. But I can’t remember a regulator behaving like that. They usually just die.

Beats me. At this point I’d probably disconnect everything from Vin and try feeding 5V from some other source direct to the 5V pin.

Steve

Hey Steve,

I tried the circuit with a new Arduino Nano this morning and it works. Looks like the old Arduino was bad. The sketch is running with no flickering LCD (the Nano is outputting 4.85v on the 5v pin).

Thanks so much for your help. Very frustrating when things don’t work because of a broken component rather than bad code or incorrect wiring.