... and then measure voltage between "5v" and "GND" again
I also tried powering it that way, and in that case the reading was totally normal—4.95V if I remember correctly.
My reasoning is this - if there really was 6.75v, the AVR controller would have failed.
So I think you are wrong with your measurement... or the controller is about to burn out.
Got it. I’ll do another measurement later—maybe I really did mess something up. Thanks!
Powering through USB is no only safer, it also allows for a higher current draw from any/all pins of the Mega. Current draw from the Mega is limited to about 200mA with 9volt on the DC socket (~400mA when powered via USB). You could have cooked the 5volt regulator of the Mega with that 9volt supply, especially when that supply was unregulated.
It seems that you have opened two threads for this problem, which is against forum rules.
https://forum.arduino.cc/t/need-help-controlling-a-multi-motor-system-with-arduino/1372700
Leo..
Got it—I'll just stick with powering it through the USB port. But do you think I should still get a new Mega board? I mean, this one does have a few issues here and there.
Sorry about that—I’ll delete the other post right away. I just wanted to describe the problem more clearly. But I’d still really appreciate it if you could take a look at the detailed description and help me out.
If I choose to power the board through USB, will that ~2.9V that's somehow coming from the mainboard itself cause any issues?
Powering through the USB port with a 5volt cellphone charger bypasses the possibly damaged onboard 5volt regulator.
But who knows what damage that >6volt has done to the processor.
Leo..
No, don't. Flag it, and ask a moderator to merge it.
Leo..
Hi everyone,
Just took over a project—basically, it's about using an Arduino to control five stepper motors and operate a syringe pump via serial communication. The person who worked on it before made a custom mainboard to achieve better integration.
Here's the rough setup.
Right now there's an issue—looks like the previous person didn’t quite understand how the power system works and mistakenly connected a 5V power supply to the Vin pin, which obviously isn’t the right way to do it. So they manually cut the wire going to Vin. But somehow the board is still getting power, and I suspect it's being powered through the regular 5V pin.
Today I measured the voltage between 5V and GND, and it was around 2.9V. Strangely enough, the Arduino can still control all five motors just fine, but the serial communication isn’t working properly.
When I connect the Arduino to my computer via USB, everything works perfectly—the motors and the pump all run fine, and the voltage between 5V and GND is 4.97V. But the problem is, the device isn't supposed to stay connected to a computer during normal operation.
So, I bought a 9V power supply and connected it to the DC jack. That’s when things went wrong—all the motors went crazy and completely out of control. I measured the voltage between 5V and GND and it was 6.75V, which is obviously way too high. To rule out an issue with the power supply itself, I tested it on other boards and everything looked normal. So the problem must be with the board I’m using right now.
Should I just get a new Mega board? Can I safely power it through the DC jack from now on? Also, could that mysterious 2.9V from earlier cause any damage to the board?
Really need help from the community on this. If you need more details, I’ll do my best to provide them. Thanks in advance!
BX
Please post real schematics. Make it contain one motor to make it easy.
That's a recipe for failure. No Arduino can be used for supplying power to motors, solenoids etc.
End of reading the post. Please post schematics. Hand drawn using pen, paper and a camera picture usually works well.
I merged the two topics as suggested.
Carry on.
Again, use a cellphone charger wit USB socket, and plug the USB lead of the Mega directly in there.
Leo..
5 volt into Vin is dead in the water. 7.5 to 12 volt is needed. You can feed 5 volt to the 5 volt pin.
Are you measure the voltage between Vin and GND rather than "5v" pin?
You should read and understand the documentation for your board. How to power the Mega is explained here.