Two power supplies to Mega?

I have a Mega project that runs off an external, 12v 10A power supply. The same power supply controls a few meters of 5630 LED strips, hence the high amp rating. I have the 12v going to the Vin on the Mega and the project works fine for the most part, however when it executes commands, the display (1.8" TFT) flickers. Occasionally it will just terminate the command and reboot. However if I have the USB cable connected to the Mega at the same time, there are no issues at all. That leads me to believe that somehow the external power supply is insufficient to power the lights and the Mega (plus attached devices).

My thoughts on solutions are to build a voltage regulator circuit that steps down the 12v to 5v and supply that through the 5v pin, but then I’d have 12v going into Vin and 5v going into the 5v pin at the same time. I’ve attached my schematic, however take it with a grain of salt because it is not up to date. The wiring from the power supply to the board and LED strips, however, is accurate and has not been changed.

Any ideas on what might be causing this insufficiency in power? Thank you.

but then I'd have 12v going into Vin and 5v going into the 5v pin at the same time.

Why? Once you add the regulator and related circuitry, disconnect the connection to the barrel jack.

Though it seems pointless to replicate the functionality built into the Arduino. Adding another voltage regulator and related circuitry won't make more current available or prevent the devices that are sucking all the current from causing the voltage to drop, resetting the Arduino, from sucking so much current.

PaulS: Why? Once you add the regulator and related circuitry, disconnect the connection to the barrel jack.

Though it seems pointless to replicate the functionality built into the Arduino. Adding another voltage regulator and related circuitry won't make more current available or prevent the devices that are sucking all the current from causing the voltage to drop, resetting the Arduino, from sucking so much current.

I need the barrel jack connected because the LED strips run off 12v. And it's not the barrel on the Mega, it's an external for the same reason. As for your second point, I agree, it seems pointless. But as it is, with both the USB and external 12v connected, the power does not flicker whereas it does with just the 12v.

I need the barrel jack connected because the LED strips run off 12v.

I need new shoes because I like chocolate ice cream. Does that make sense? Neither does your statement. How you provide power to the Arduino has NOTHING to do with how you power the LEDs.

But as it is, with both the USB and external 12v connected, the power does not flicker whereas it does with just the 12v

The LEDs consuming too much current can not cause the USB voltage to drop.

With 12V connected, to barrel or to Vin, when Vin/2 is > 3.3V that source will be used to make 5V. If Vin/2 drops to less than 3.3V, USB source is used if it is connected. You could look into driving 12V into the Barrel and adding a large electrolytic capacitor to Vin/Gnd to help buffer any fluctuations at the barrel jack - the reverse polarity protection diode between the barrel and Vin will prevent the cap discharging into the apparently overwhelmed 12V supply. 100uF or more, experiment to see how much is needed to prevent reset and flickering.

I suspect an overheating onboard 5volt regulator.

When the onboard 5volt regulator shuts down, USB supply takes over. So you won't have a shutdown with USB connected.

Not wise to connect 12volt to the Mega's Vin. Always use the DC jack. That also shaves 0.7volt of the already too high input voltage. If that's not enough, use four 1N400x diodes in series with the +line to drop the voltage with another 4x0.7volt. Leo.

To explain further. The Mega uses a fet to switch between onboard regulator and USB supply. But that only works one way. It stops backflow into the PC, but it doesn't stop power from the PC to the Mega in case the onboard regulator cuts out. Because of a reverse diode inside the fet.

PaulS: I need new shoes because I like chocolate ice cream. Does that make sense? Neither does your statement. How you provide power to the Arduino has NOTHING to do with how you power the LEDs.

If you would look at the schematic I originally uploaded, you will see that the LED strips and the Mega run on the same 12v source. However I need new shoes and I like chocolate ice cream, too, what a coincidence.

Wawa: I suspect an overheating onboard 5volt regulator.

When the onboard 5volt regulator shuts down, USB supply takes over. So you won't have a shutdown with USB connected.

Hmmm, I suspect you're right. Now that you mention it, I've noticed that it does only happen while running particularly "heavy" sections of code that use the 5v. I could use the existing barrel jack as you recommended, but I'll have to "split" the power coming from the wall wart to power the Mega and the LEDs separately instead of running them in-line as shown. I'm wondering if space will allow for that.

Connect +12volt via a series string of diodes to Vin. Every diode drops 0.7volt. Drop it below ~9volt.

I use a small buck converter for my Mega. Drops 24volt LED supply to 7.5volt for the DC jack. Then the reverse protection diode and onboard regulator have an easy job dropping it to 5volt. Leo..

majhi: If you would look at the schematic I originally uploaded, you will see that the LED strips and the Mega run on the same 12v source. However I need new shoes and I like chocolate ice cream, too, what a coincidence.

i think either you or WE are missing something here. if you changed your power supplies and your LEDS run off one power supply and your Arduino was to run off a different power supply (USB) why would you need a second power source to the Arduino?

power your LEDS the way they are powered now. power your Arduino separately. there's nothing else needed

and yes i looked at the schematic