LN298N blown up my 3rd arduino? :(

Hi guys,

My first post, so thanking anyone willing to help me out in advance!

I'm trying to make a basic arduino car to drive forward and backwards.. I'd like to add ultrasonic sensors etc later, but I can't get the basics working!!

I have a 12v battery pack branched off to power the LN298n and the arduino port through the power socket (I figured this would be better than adding a jumper from the 5V to the arduino, which I understand can damage the board if you forget to unplug when you connect it to your computer.)

Issue is.... I am now on my 3rd board, where I have been able to upload my program, but after a little while the port won't recognise anymore and I can't upload anything!!

Is there something obvious I'm missing?!! I think I've killed 3 boards now!!

Diagram of how it's wired here:

Photo of my setup here: Dropbox - 20181021_195046.jpg - Simplify your life
Video of my robot here:
Dropbox - 20181021_194716.mp4 - Simplify your life

jessvuso:
Is there something obvious I'm missing?!! I think I've killed 3 boards now!!

So, if you take your bare (suspected to be broken) UNO with nothing connected to it except for the USB cable (for USB communications and for powering the UNO), your observations are suggesting that WINDOWS no longer assigns a COM PORT number (in DEVICE MANAGER), right?

Yes that’s right, it starts off happily uploading whichever program I like, I unplug and run the program for a while using the 12v to power my board and motor shield… then I unplug 12v from the arduino and replug to my computer and the COM PORT has disappeared… but permanently, as the ‘port’ option is greyed out in the tools/port list!

Light still turn on the arduino AND the motor shield whether attached to the computer or the 12v, but wheels don’t turn, although the motor shield lights indicate the program is working as expected.

To add to my pain… I have 12 x year 10 students working on these and they are getting frustrated, I’m trying to stay a step ahead but I’m not winning!! Thanks in advance!!

So when it no longer recognises my board, I've grabbed another one, selected the port, but in time faced the same issue.. so I now have 3 boards that won't be recognised... thankfully I have more boards but I'm loosing the confidence to plug into the 12v..

jessvuso:
but I'm loosing the confidence to plug into the 12v..

I would have lost confidence after the first failure.

Please make your images visible here - See this Simple Image Guide

...R

Your actual wiring does not match your schematic. I see all the black wires connected together.

The motor black leads do not get commoned to the negative of the supply.

You should also provide a separate signal ground wire between the Uno and the driver board, using the power common is bad practice.

Thanks Robin2, I will use the correct photo format next time.

Also thanks WattsThat - I think the details of my wiring are lost in the photo.. it is definitely wired as in the diagram.

But the good news is.... I've solved it!!!! I had to add a cap on my motor board to connect the 5V and EN pins!! Now it works perfectly. I have no idea why this worked.. I also don't know how I killed 3 boards in the process, but it seems to be ok now.

Thanks for your time!!

jessvuso:
I had to add a cap on my motor board to connect the 5V and EN pins!!

Good to hear. So what was the main issue? Did you mean that you forgot to add something that was supposed to be (or meant to be) added?

Yep, that was the only issue!! It's a little cap that connects the 5V and the EN pins on the L298n board... it should have been on there, but must have fallen/been knocked off while I was fiddling around. After a serious game of spot the difference with a 2nd robot that I did get working, it turned out to be the magic answer!! I don't know why those pins need to be connected by the cap, but I can confirm that it is essential! :slight_smile: