My first standalone board

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1

Hi all,

Finally my standalone system is (almost)ready, up and running. The board is based on an Atmega328-au and features an accelerometer and gyroscope as sensors. A micro sd card reader with a low-level shifter.

I've designed the following schematic, together with some help from the forum.
The whole thing just works like a charm, my measurements are proper and the data logging is OK, I don't measure any noise at the regulators or whatever. The only thing I'm scared of is the following, the low level shifter is getting hot, very hot, and i guess it has to do with the following; when I connect a scope to 1Y and the ground I measure a oscillation close to 16Mhz (clockspeed), i guess this isn't the aim. The complete board also needs 0,5Amps (I guess this has also to do with the oscilation)

Does anyone have any idea what the problem could be for getting this hot or can I neglect it? I need to measure for a longer period of time and thus the system should be reliable.

Schematic;

The print before reflow soldering;

2

I'm sure you've already verified the schematic, looked for shorts and reversed chips and so forth.

0.5A is very excessive. I'd have guessed this board to be in the sub 100mA league. I'd take that chip out and and power it up on its own for testing. It's definitely not something to ignore.

What did you use for reflow? Hot air, oven, skillet?

3

"when I connect a scope to 1Y and the ground I measure a oscillation close to 16Mhz "
What is the state of the input pin when that occurs?

4

Pin 15 is not grounded ,should it be ?

5

The Pin 1-8 edge of the body is likely to have a bevelled edge. Check for that, see if the part is installed reversed. You would be far from the first to have done that.

6

The pin's are connected OK and as far as I believe it isn't a problem to leave pin 15 floating.