bricked two megas using motor shield - advice please!

Other Hardware Motors, Mechanics, Power and CNC
1

Hi all,

Could I get some advice please before I damage any more!

I think I've bricked two mega 2560's. Well, actually the first one seems totally bricked (red led comes on and stays on when powered by usb, nothing when powered by dc, and never gets recognised on the serial port), and the second doesn't come on at all when powered by dc but works ok with usb power. Testing it with a multimeter shows the voltage regulator on both is damaged.

I don't know what caused the first one but I do know what I did to the second...

I'm using the arduino motor shield (Arduino Motor Shield Rev3 — Arduino Official Store).

It was working ok, but one of two things happened - either 1) the load was too heavy for the motor, or 2) the shaft was slipping in the coupler. Either way, as I was testing it, I could smell some burning so unplugged.

The motor is a 12v, 65pm, worm gear reduction motor.

When I realised the red light issue, I read up on it and used a multimeter to measure the voltage on the regulator and found it was outputting about 2v or less from the 12v input. The 5v output pin is also outputting about 2.Xv.

Then I went to test the regulator on another mega 2560 I have to check how it should work, and it was perfect (12.Xv in, just a bit less out) and I accidentally connected the pins and managed to damage that one too (this is the one the usb still works on though, so it's only damaged the regulator - the other one clearly has more damage).

So - to get to my question (hope you are still reading!) - what could have caused this on the first one and how can I prevent it from happening again? I'm 'ok' with blowing two arduinos, I'm fairly new to them so it's part of the learning curve, but I do need to learn rather than keep repeating mistakes.

I had one motor attached to the A terminals, and I had 12v attached to the power terminals next to that from a power supply using a dc barrel I soldered on to two wires. Polarity is correct.

The test code was the basic code for setting the direction, disengaging the break, and starting the motor spinning.

Is there anything obvious that could have caused this?

Thanks
J

2

One thing I've noticed tonight using the mega that still works via usb but not via dc...

If I plug the arduino in to the usb without the 12v power to the motor shield (I'm using 12v motors), then the shield comes on and lights up correctly. If I then add the power to the motor shield, the motor spins.

But if I have the 12v going to the shield first, and then I plug the usb in for the mega, it doesn't turn on.

is this normal, or because or the damage I've done to the regulator?

could something like this have caused it in the first place? is there something I'm not aware of about the power usage?

thanks

3

jago2:
One thing I've noticed tonight using the mega that still works via usb but not via dc...

Looks like blown regulator.... maybe possible to replace the regulator.

4

jago2:
But if I have the 12v going to the shield first, and then I plug the usb in for the mega, it doesn't turn on.

What doesn't turn on? Shield or mega? When writing.... read over it to try avoid ambiguity.

So.... with plain mega .... no shield... the mega no longer turns on when powered by dc adapter, right?

Maybe the motor shield is destroying the mega. Try a second motor shield of same kind.... for testing.

5

Sorry for the ambiguity. I meant the arduino doesn't turn on.

I've just read the suggestion in the officials docs about cutting Vin Connect on the shield when using over 9v for the motors. Maybe that is the problem. Not sure how I missed it originally.

It obviously won't help the two damaged arduinos but hopefully may help prevent more being damaged.

But to answer your question, yes, plain mega, no shield, dc power, it doesn't work. USB power does. I've damaged the voltage regulator. This is the one where I did it by mistake trying to test the regulator and connecting pins by mistake.

The first one to die, using the shield, also has a damaged voltage regulator but doesn't work even with USB power so I suspect it's totally fried.

But for the price, it's not the end of the world. I'm more concerned about it not happening again and hopefully cutting the Vin Connect pin on the shield is what I need to do?

6

Cutting VIN Connect on the back of the motor shield now means the mega starts even when the power to the motor shield is on, so that's an improvement and a lesson learnt.

Whether that had anything to do with burning the first board I don't know but ... finger crossed it doesn't happen again, and in regards to the second damaged mega, I'll be more careful next time using a multimeter on a voltage regulator :wink: