Arduino Prototype is leaking power somehow?

Hello all,
I’ve been working on an Arduino project involving a board with an AVR 1284P and FT232rl for a long time. It’s my kickstarter project and its in the final development. I need help figuring out where some of the power is going.

So my device piggybacks onto an Xbox 360, and they both share a power source of 2 AAs. As soon as my device is connected the LEDs on the Xbox 360 controller dim greatly. This has only started after I switched the AVR on board to a 1284P from a 328P.

When I measure the current draw in series with my device the the multimeter is showing between .1 and .2 ma (or .1 or .2 on the 20m setting). I find it strange that as soon as I changed the device’s AVR to a 1284P it started to affect the Xbox Controller. I’m not an EE but could it just be that the device is stealing a lot of the Power Supllies Potential Energy (so basically its voltage?) I’m starting to think that it’s not actually a power hog its just that the controller in some way is not allocating enough voltage/current to its LEDs with the added strain. I believe this because if I ground the Xbox Controller LED with my device the LEDs shine brightly. Would this demonstrate that it actually isn’t the lack of current but something else.

Also, If I connect the Xbox Controller’s USB cable the LEDs work correctly and shine brightly. This would be because the battery packs 500ma supply potential plus the 500ma of the USB can supply enough current for the entire load? The LED shines with 1.71 volts with my device attached and with 1.86 with it not attached. This would indicate a current shortage?

My first thought was the pull up were leaking current into the controller’s ground on some of the analog buttons but after disconnecting all other connections besides VCC and Ground the change was little.

The controller still works correctly, just the Player LEDs are extremely dim.

If some of this doesn’t make sense please ask me in more detail. This project is open source and I can also supply schematics and other info if need be. The concept is pretty cool and I’ve already created a custom library to interface will all of the controllers buttons and peripherals.

battery packs 500ma supply potential plus the 500ma of the USB …

Big NoNo.

If your device is to be battery powered, the USB must not power the Mega.
Common ground is required, but you must keep USB +5V and battery +? Volt separate is USB powers the Mega.

Thanks for your reply but the USB does not power the Mega. It only powers the controller when it is plug in. This part is not under my control. The USB cable is disconnected is not involved at all for what I am talking about.

they both share a power source of 2 AAs. As soon as my device is connected the LEDs on the Xbox 360 controller dim greatly

Do you own a DVM? Likely the batteries are suffering from a voltage drop with the extra load. Different battery chemistry has different internal resistance. As it us resistance, a voltage drop is inevitable as the drain current is increased. http://batteryuniversity.com/learn/article/the_secrets_of_battery_runtime

Ray

This voltage drop is exactly what I think is happening. My question is why? There shouldn't be much load from just an AVR 1284P at 8mhz. Before when I used a 328P I didn't have this problem but I did change other things aswell. Could a decoupling cap cause this? Should I add a resistor in between the boards vcc and the controllers battery pack?

Could a decoupling cap cause this? Should I add a resistor in between the boards vcc and the controllers battery pack?

No, and no.

I suspect the additional current from the 2560Mega is the culprit. I assume you are feeding the battery positive directly to the Mega +5 header pin? (Not through the barrel power connector.) Looking at the schematic, you have 2 microcontrollers to power, several LEDs, and various pull-up resistors. My guess is the Mega2560 just takes more energy to run.

Did you upgrade from the atmega328 to the atmega2560 due to I/O pin needs of because of SRAM/flash requirements?

Ray

I initially upgraded for more pins and now I am using them all. For reference, it is a custom board not a mega board. The 1284P is in an entirely different class than the 2560.

I think the pull-ups are the culprit. The pins are usually all set to input and they need to be. If they are set to output every they interfere with the controller, which is sometimes the point but not always. I can provide the schematic if need be, as soon as I release the boards to the public it will have to be anyway, its open-source.

I think the pull-ups are the culprit.

RRST - Reset Pull-up Resistor: 30 k? min, 60 k? max Rpu - I/O Pin Pull-up Resistor: 20 k? min, 50 k? max

Do the math...

The 1284P is in an entirely different class than the 2560.

Darn spell-checker!

Ray