Mega Rebooting loop on 12V Power

if i plug in an external 12v power into the mega i'm getting a reboot loop after about 20 seconds

whats going on?

Is the 5v regulator getting hot? It might be going into thermal shutdown, so the uC reboots as it shuts down, cools a little, and restarts.

i didnt feel it as its hard to get to get to…
due to having a shield fitted and a proto board on top of that

im coming to the final stages of the project now so its all ready to fit into its box

i’m just trying to get it powered from one power supply and not the USB
PDF attached is how i am at the moment but it wont work this way

but this is what i wanted

Wring.pdf (798 KB)

12V is pushing it without peripherals attached, so its pretty certain the on-board regulator
is overheating and shutting down.

Maybe use a switch-mode dc-dc converter from 12V to 5V, or at least power the screen
via an external 5V regulator so that current is not going through the tiny on-board regulator.

CrossRoads:
Is the 5v regulator getting hot? It might be going into thermal shutdown, so the uC reboots as it shuts down, cools a little, and restarts.

He's driving a TFT and an RF device off the Arduino 5V regulator. I'll bet you're right. The regulator is overheating, going into safe mode, then cooling off and repeating the cycle.

When I've run into this problem, I tried to put a TO-220 7085 in parallel with the on-board regulator but it doesn't work (the on-board still gets hot). What I have to do is carefully unsolder and lift the right-hand-most pin (the Vin) of the on-board regulator a few mm off the board to disconnect it. Then the external 7085 does it's thing. And, if necessary, the on-board regulator can be re-enabled simply by soldering the pin back in place.

Krupski:
When I've run into this problem, I tried to put a TO-220 7085 in parallel with the on-board regulator but it doesn't work (the on-board still gets hot). What I have to do is carefully unsolder and lift the right-hand-most pin (the Vin) of the on-board regulator a few mm off the board to disconnect it. Then the external 7085 does it's thing. And, if necessary, the on-board regulator can be re-enabled simply by soldering the pin back in place.

Unfortunately, putting regulators in parallel won't work as they are all a bit different in output voltage, and the one with the highest voltage will power the load and the other won't do anything.

I see no reason to desolder any leg. Just use the external heatsunk 7805 or similar and pipe it's output to the 5V-pin on the Arduino.

// Per.

i think i will try and power the screen via the 5v supply first. but just a quick question will this not affect the logic voltage coming from the screen, i have a SD card in the screen what i will be using

Why a 12volt supply.
Replace it with a 7.5volt (or 9volt) regulated supply, and your troubles are over.
Leo..

Zapro:
Unfortunately, putting regulators in parallel won’t work as they are all a bit different in output voltage, and the one with the highest voltage will power the load and the other won’t do anything.

I see no reason to desolder any leg. Just use the external heatsunk 7805 or similar and pipe it’s output to the 5V-pin on the Arduino.

// Per.

Very true. The reason that I did it is that I have a “development module” built (sort of like a super “Esplora”) and I needed to be able to plug in my 13.8 volt DC power supply into the MEGA power jack, but still be able to power all the things on the module (which include several VFD displays, a TFT display, an RF transceiver, a serial adapter, etc…).

So my MEGA is attached to the top, and underneath is a 7805 on a heatsink. 13.8V goes into the MEGA, out the “Vin” pin to the regulator and from the regulator back up to the “5V” pin. So my on-board 5V regulator needs to be disabled (which is why I lifted the one pin).

Here’s my messy Arduino development area!

(click for full size)
my_esplora.jpg

Krupski:
Here’s my messy Arduino development area!

(click for full size)
my_esplora.jpg

I now officially hate you (just a bit envious of those VFD’s) …

// Per.

Zapro:
I now officially hate you (just a bit envious of those VFD's) ...

// Per.

The nice 128 x 64 graphics module (directly to the right of the red voltmeter displaying an "analog clock") you can get direct from Noritake for $38 USD. The other ones are even less. It's got both a parallel and SPI interface, and there's an Arduino library for it:

GitHub link

Buy one and have fun!