Powering Leonardo w/ PSU and Reading Serial Monitor

Hi, I’m new to Arduino. Sorry if my post is long but I know its good to have all the facts.

I am trying to power my Arduino Leonardo with a AXT power supply, I also want to view the serial monitor via the micro-USB port on the board.

I have looked around at other posts and none really come close to what I am dealing with.

How its wired (See Image): I am using only 3 wires from the ATX connector: +12v, COM (GND), and PS_ON#. I have a switch connected to the PS_ON# and COM so that I can turn the Power Supply on and off. The +12v and COM are connected to a power distribution board which is where the barrel jack to power the Arduino is connected to.

All of that works great, now to my problem.

While the Arduino is connect via the barrel jack, if the power supply is unplugged, all switches off, but the Arduino is connected to the computer via the micro-USB, the Power Supply Fan starts to spin. After I saw this I disconnected the USB and then the barrel jack from the Arduino.

I then reconnect the Arduino to the computer via micro-USB and now Windows 10 will not recognize my board. I hear the connected then I hear it disconnect. Somehow I can still upload code by hitting the reset button right when the IDE starts to say uploading. But I cannot view the serial monitor since the computer doesn’t see the connection to the Arduino.

I know Leonardo boards seem to get this issue often (according to other posts) so I might need a different board (I currently only have the one).

But what do I need to do to the circuit to fix the issue of my PC powering the Power Supply Fan through the Arduino?

Thank you in advance

The fan coming on indicates that the PC is under load. It's powering the whole circuit through the USB. (If I am interpreting the location of the fan correctly.)

Here's the original photo...

Is that really how it's wired? Nothing to the Leonardo except the barrel jack? Then it should not be able to power anything out that jack. There's a diode there to stop these kinds of problems.

It may be possible that your PC and the ATX power supply are connected elsewhere, maybe through the mains socket. Then there could be damaging current flowing in the ground wires, that isn't blocked by any diode.

So here is how it is actually wired.

So I'm pretty sure that the PC is powering the power supply fan which is should not be since the Arduino should have a diode...

If for some reason it doesn't have a diode, what would be the proper way to implement a diode in the current wiring?

Sorry I cant get the image to be in the text so here is the downloadable one.

Use the [ img ] tag. But you have to upload the picture by posting the post to get the address to use in the tag.

So I think I misunderstood the location of the fan. You mean the fan in the PSU? The diode in the Arduino should definitely prevent that happening. Something is wrong.

I did a test to see if I could read a voltage from the barrel jack when the Arduino was only pluged into the computer via the micro-USB port.

The circuit is: PC to Arduino Leonardo via USB to micro-USB. Then Arduino Leonardo to voltmeter via barrel jack to voltmeter leads.

I read 4.465 volts from the barrel jack when the computer is turned on and connected to the Arduino like how I stated above, meaning the computer is supplying power through the Arduino to the barrel jack. There must not be a diode or anything stopping the flow of electrons to go out from the barrel jack.

Thus, where would I add the diode to stop this? Should it be in series from the power supply to the Arduino via the positive lead before the barrel jack?

Never mind, just found this post...

The Leonardo board doesn't have a series diode just an anti-parallel protection diode.

Now I just need to learn how to read the schematics so that I don't ask a simple answer question like that again..

Thanks for all help MorganS