Making a portable Bluetooth headphone amplifier

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Making a portable Bluetooth headphone amplifier

Postby Lanyind » 05 Mar 2018, 03:57

I made my own diy "bare bones" Arduino Due in an embedded application. Basically I was making a portable Bluetooth headphone amplifier for a school project. The point of the MCU was to display battery information on a touchscreen LCD and to control volume with a digital resistor( Everything else on my board seems to work including Bluetooth. Since this was a prototype, I added a switch which would bypass the digital resistor and go to a normal pot for volume control, so I know everything on my board works except the SAM3x8E.

Here is the issue:

When I plug in the USB, the device does not get recognized by the PC at all. No COM ports are available in device manager. If I press the reset button, the chip gets abnormally hot. Uncomfortably hot to the touch! If you unplug power and plug it back in, even after waiting a second or two, it STILL starts getting hot. It's only after you power cycle and hit the ERASE button a few times that the chip finally stops overheating. Also, during this process, my 3v regulator drops out as if the chip is drawing too much current. (because the blue 3.3v led goes out)

After the power cycle, things go back to normal, and Bluetooth and the rest of my amplifier works fine. Can anyone take a look at my schematic and see if anything obvious is wrong? I am a little lost, any suggestions to help diagnose this issue?

Tomorrow, I will hook it up to an oscilloscope to make sure my crystals are providing clock. Any other test I can perform? I have triple checked this schematic against a number of Arduino Due and SAM3x8E reference schematics and do not see anything obviously wrong.

Here are the Eagle Cad Files:

Also some photos:

Here is the actual board (don't mind the unsightly makeshift jumpers):

Also, here is a schematic of the Power circuit:
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Re: Making a portable Bluetooth headphone amplifier

Postby Sir Cumference » 05 Mar 2018, 17:21

This really is quite off topic for a self bondage forum.

An impressive project if you’ve made all that!

I dont know how you’ve managed to make a huge and low resolution photo, but it is quite impossible to see if there are any errors in the circuit. It probably would too, in a high res photo.

Whenever I’ve built something and a part of it overheats, I may be absolutely certain that I’ve wired everything correctly.
In this case you have designed it yourself, making a myriad of errors possible.

It always ends up being the case, that I have connected something wrong, have put something in backwards or have placed a blob of solder somewhere to create a short circuit.

The most likely answer is, that you goofed somewhere.
~ Leatherworking, blacksmithing , woodworking and programming are the most pervertable skills you can learn! ~
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Sir Cumference
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Re: Making a portable Bluetooth headphone amplifier

Postby lj » 06 Mar 2018, 09:35

sounds as though you have a power supply issue - something that gets hot is generally suffering from a fault. If it carries on suffering when briefly powered down and re-connected, this suggests a latch-up caused by two circuits battling over power supplies. A simple cause would be a 5v USB input on a circuit running at 3.3v.

If you power down AND separate the USB device, and this clears the fault on re-powering, then do the same power down with the USB connected and the fault re-starts, then that proves the problem is power related.
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