Hello,
I've been using my Mega 2560 for some time now but the last time I connected it to my computer it stopped appearing as a device/COM port. I'm using Windows XP SP3 - the computer doesn't appear to register it's connection any more.
When I connect the USB cable, the power light appears on the board and the orange light near pin 13 light up.
When I press reset on the board the orange light blinks.
I've tried 2 different USB leads and 2 different computers. On neither computer does it appear to notice that the Arduino has been connected - i.e. nothing shows up in device manager and when I view hidden devices the Arduino is greyed out. The Arduino IDE says it can't find anything on COM5 (its old port) as one would expect.
The board appears to be able to run the last sketch I uploaded but it's difficult to tell how well it's doing it since I'm also debugging the circuit..
The last time I used the board I had connected to 5V external power at the same time as the USB - I'm not sure if that was a mistake and I've fried something.
I can't run the loopback test as the board isn't showing up as a device etc. and I can't find any other troubleshooting instructions at this point.
The last time I used the board I had connected to 5V external power at the same time as the USB - I'm not sure if that was a mistake and I've fried something.
If you applied the 5v to the 5v bus and the USB power at the same time, you could have fried the USB IC. This is from the Mega 2560 products page.
The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
Ah ok. I'm building a robot with an onboard 12v NiMh battery. I was powering the motors with that and using a 5v output from one of the motor controllers to power the Arduino. I'd wired that 5v into the 5v pin of the Mega which was clearly a mistake.
What's the best setup to achieve what I'm trying to do? Should I wire the 12v battery direct to the DC jack input (or Vin does it matter?) of Arduino? if I do this, do I still need to be careful to disconnect when I plug in the USB? If there's a good article on this feel free to point me in the right direction.
As a side note, how repairable is my old Mega - the rest of it seems fine, it still plays the last script I guess I fried the serial comms...
The best way I have found for powering the Mega (or any Arduino with USB) with a 5 volt supply is use the USB port as the power supply. You can purchase USB cable parts at Adafruit.
edit: I just checked at Adafruit, and noticed they do not carry the USB standard B-type plug, but DigiKey does.
If you want to power via the 5V header pin, connect a diode from 5V (anode) the Vin (cathode) to prevent reverse driving the 5v regulator.
See page 10-11.
@CrossRoads: That is apparently not the only problem with powering the Mega with the 5v bus. If the USB is powering the Mega, and the 5v bus is being powered directly, The USB power bus and the 5v bus are connected with a FET, and that causes the USB IC to fail.
Take a look at this schematic. The thread link I posted above that deals with this has this solution if you want to prevent damage. You must remove the FET T1 (bottom of the schematic). If Vin is not greater than 6.6v, the USB and 5v power buses are connected, and that appears to cause the USB fail.
edit: ...and sometimes the fail is not immediate. The thread link above describes the fail and the cure. I cannot see why that would cause the IC to fail, but it does. ??
Yes, odd. Would think the stronger source (5V at header, slightly higher than 5V from USB after it drops a little thru the PTC) would just power everything.
I don't use any Megas or Unos myself dual powered like that, so have never seen this.
If I do use an Arduino, it's almost always an older Duemilanove or a Promini.
sabrown:
Ah ok. I'm building a robot with an onboard 12v NiMh battery. I was powering the motors with that and using a 5v output from one of the motor controllers to power the Arduino. I'd wired that 5v into the 5v pin of the Mega which was clearly a mistake.
What's the best setup to achieve what I'm trying to do? Should I wire the 12v battery direct to the DC jack input (or Vin does it matter?) of Arduino? if I do this, do I still need to be careful to disconnect when I plug in the USB? If there's a good article on this feel free to point me in the right direction.
As a side note, how repairable is my old Mega - the rest of it seems fine, it still plays the last script I guess I fried the serial comms...
Many thanks,
Simon
When I wish to power an arduino board with an external regulated +5 vdc I usually just take an old USB cable and hack off the PC end, fish out the +5vdc and ground wire and wire that to the regulated +5 vdc voltage source and then just plug into the boards USB connector. The added advantage is that it's easy to power off the board by just unplugging the cable.
sabrown:
Ah ok. I'm building a robot with an onboard 12v NiMh battery. I was powering the motors with that and using a 5v output from one of the motor controllers to power the Arduino. I'd wired that 5v into the 5v pin of the Mega which was clearly a mistake.
What's the best setup to achieve what I'm trying to do? Should I wire the 12v battery direct to the DC jack input (or Vin does it matter?) of Arduino? if I do this, do I still need to be careful to disconnect when I plug in the USB? If there's a good article on this feel free to point me in the right direction.
As a side note, how repairable is my old Mega - the rest of it seems fine, it still plays the last script I guess I fried the serial comms...
Many thanks,
Simon
When I wish to power an arduino board with an external regulated +5 vdc I usually just take an old USB cable and hack off the PC end, fish out the +5vdc and ground wire and wire that to the regulated +5 vdc voltage source and then just plug into the boards USB connector. The added advantage is that it's easy to power off the board by just unplugging the cable.