Arduino Due: external power supply and USB connection

Hi everyone,

I'm having some issues with my Arduino Due and connecting an external power supply and USB connection. To give the context to my project I'm building an ultrasound circuit and there are connections between the circuit and Arduino, as seen in the diagram.

The issue:

I insert the USB to the Arduino and upload the code. Then I plug in the external power supply and Arduino seems to disconnect every time I insert the external supply. Then I turn on the circuit supply and nothing really happens because I'm disconnected from the COM5.

Another issue is when the in insert both the USB and external supply before turning on the circuit supply, The circuit supply is warning me the current is going over the maximum limit of 1A. ( My circuit supply is two DC bench power supplies set to 9V/1A to get +9/GND/-9). I decided to test the pin voltage at specific pins.

Vin: 6.38V
5V: 2.72V
Pin 5: -3.14V
Pin A7 : 3.14V

I'm not really sure what's happening but I've tried resetting the Arduino and changing external supplies but the same thing keeps happening. Also, another thing to add is when the circuit supply warns me of the overload of current I take out the wire connecting to Pin 5 and re-insert it back in and the current level goes back to normal ( around 0.10-0.12A).

Sender Circuit Diagram:


Sender Hardware wirings:

Receiver circuit diagram:

Receiver wirings (red wire to the far right is the connection to pin A7 on Arduino)

Arduino diagram:

Arduino wirings:

Is the GND of the Arduino connected to the GNDs of the proto circuits? In your diagram, that could only happen through the barrel jack.

Also, where is the voltage level translation between the Due 3.3V and the 9V on your proto boards?

@aarg, yes the GND of the Arduino is connected to the switches you see in the diagram, but they are built on a separate part of the breadboard from the rest of the circuit. The supply jack is already grounded.

If the GND's are connected, can you please explain how, in detail? There are 3 main sections, RX, TX, Arduino. How are the grounds between them connected?

First of all, how is the ground from the Arduino extended? Barrel jack? Pin connection that isn't shown?

Honestly, though... I think your level translation issue is more serious...

Sorry, I'm not quite sure what you mean. I only use one GND pin from the Arduino board and that's to attach the 10kohm resistor to it from the breadboard. The only pins I use are the ones seen in the diagram.

Electricity goes in circles... :slight_smile: You can't just connect signal pins without a common.

Yes, I know that. My signals coming from arduino are grounded ( seen in the diagram)

Grounded how? Anyway, as I said, you have connected 9V signals directly to the Due pins. That can permanently damage the Due I/O pins...

What I see in the diagram, is a ground symbol extending from each board, with a connection point. There is nothing in the diagram itself that suggests how or if those are interconnected.

When pin 5 is connected to the breadboard there is a 1nF capacitor, where one side is grounded and the other is attached to the signal. As for pin A7, the signal is connected in series with a 3.3V Zener diode and 100ohm resistor, where one side of the Zener diode is grounded.

Your "trigger" signal is powered by 5V and there is DC continuity through to the Arduino input. The 1nF cap doesn't block DC, it's configured as a low pass filter.

What do you think is a possible soultion then? Because arduino still dsiconnects when I connect the external power supply and a negative voltage still appears on pin 5 when I measure with a DMM.

It could be because of the ground connections I'm talking about. Please post (edit -larger) images of your actual hardware. Generally we need better diagrams.. for example you talk about "pin 5" - it's a struggle to identify that on your diagram...

I've added a wiring diagrams and hardware connection pictures, hopefully it's a little bit clearer.

Somewhat, thanks. So as I mentioned, the only ground to the Due is via the barrel jack sleeve. Does that connect somewhere to the other grounds? If so, where?

No, the ground from the barrel jack does not connect anywhere else.

Well, a circuit is incomplete without a return connection... like I said before...

But I thought the barrel jack was already grounded? Therfore there is a "circle". How would I connect the ground from the barrel jack sleeve to other grounds?

Sorry if this is repeitive I just though the jack was already grounded.

Grounded to what? It's only grounded if you ground it. Generally the barrel power plug just goes to a wall adapter. That's isolated from any service ground, for safety reasons.

But I suggest you fix the 5V on 'trigger' first, so you don't blow up the Due input when you finally make it work.

The wiring of 2 switches on the diagram and on the board below seem to be different

Yes my barrel jack plug is conencted to a wall adapter.

There isn't 5V on the "trigger" pin ( or pin 5) there's a reading of -3.14V when connected with the supply. There's a 5V reading on Vin, which doesn't make sense due to it being a 9V supply.