Think I fried Arduino

[metrologist]

I plugged in an RC ESC, the ground and data pin only from ESC to Arduino, then a 9V wall transformer for power to the ESC. At that point, the Arduino was already plugged into the PC, all Arduino LEDs came on. No comm with the Arduino.

My suspicion is that there is a ground loop so the esc was at a different ground potential than the Arduino and there was current through the ground leads, but I measure the voltage between grounds with a DMM and there is no mv difference.

Now why has my Arduino burned out? Or maybe it is ch340 chip. PC still recognizes ch340 though.

[Ian.M]

So what's the voltage difference between the wallwart 0V and your PC chassis?

[metrologist]

That is what I measured is 0 mv, just flash a few tenths. It's all plugged into same mains outlet, but walwart does not have earth ground. I cannot see the esc having output on the digital pin to cause this problem, but that is all that is plugged into Arduino is ground and the data lead from the esc.

I am using the exact same setup with Arduino and DRV8825 - same walwart to DRV driver for the motor, and it has been working for days.

[rstofer]

Pretty hard to discuss the problem without schematics and datasheets.  Wiring diagrams...

After you disconnect everything from the Arduino, does it work?  If not, it probably gave its life to protect your PC.  It is not unheard of for these kinds of problems to take out the PC, USB controller and/or motherboard.

http://electronics.stackexchange.com/questions/94382/what-measures-should-i-take-to-protect-the-usb-ports-of-my-pc-during-development

Unfortunately, optically isolated hubs tend to cost a bunch.  I use a powered hub and hope for the best.

[Ian.M]

Cheap Adum4160 based USB isolators can now be found on EBAY and AliExpress.
See https://www.eevblog.com/forum/reviews/chinese-usb-isolator-test/
They need some mods done to add an external floating regulated 500mA 5V supply and aren't suitable for high voltage use, but will prevent ground loops or moderate potential differences frying your PC

[metrologist]

Wiring is so easy, did not seem necessary. I do not have datasheets for anything other than the Atmel chip. The ESC is a cheap red shrink wrap CE with the SimonK firmware and the motor is one of those A branded CE, cheap. The wallwart is one of those radio shack brand switchable 1.5-12V 800 ma linear supplies (not switching).

It looks more obvious now when seeing the positive from the walwart contacting the ESC before the negative. One might have thought there was isolation between the logic side and high power motor side of the ESC, but then now I also remember there is this goofy thing the RC industry came up with called BEC - battery eliminator circuit, which just regulates the motor side power to logic levels and ports that to the logic power and ground must then be common on this device.

[rstofer]

Cheap Adum4160 based USB isolators can now be found on EBAY and AliExpress.
See https://www.eevblog.com/forum/reviews/chinese-usb-isolator-test/
They need some mods done to add an external floating regulated 500mA 5V supply and aren't suitable for high voltage use, but will prevent ground loops or moderate potential differences frying your PC

Bought a couple.  Interesting...

[metrologist]

I decided to remove the Atmel chip. It was difficult because I was too lazy to remove the top mounted female headers, so I cut the pins straight down next to the chip with a very sharp exact-O. Looks like I lost no pads - amazing! But the chip seems to cost more than I can get a whole new Arduino mini. ?  Maybe I can get the ch340 off and put it on a proto board or just use the beheaded mini as a programmer, since the pack of "programmers" I bought do not have a DTR or reset on the pinout...

[Nusa]

I decided to remove the Atmel chip. It was difficult because I was too lazy to remove the top mounted female headers, so I cut the pins straight down next to the chip with a very sharp exact-O. Looks like I lost no pads - amazing! But the chip seems to cost more than I can get a whole new Arduino mini. ?  Maybe I can get the ch340 off and put it on a proto board or just use the beheaded mini as a programmer, since the pack of "programmers" I bought do not have a DTR or reset on the pinout...

I had one of those annoyances. DTR is still available on the CH340G chip, pin 13, even if it they didn't break it out. I soldered a short bit of wirewrap wire to a single header pin, then tagged the other end to pin 13. Hotglued the pin to the top of the IC for use. Fixed!

[metrologist]

The little USB serial things I got have enough pins, three are used with a jumper to set the 3.3/5v level. I was thinking of cutting the traces on two of those pins and solder bridge the traces to set the voltage. That would give me two extra pins on the existing header. Worthy of a thread maybe?

[retrolefty]

Arduino forum has a sticky post about performing a 'loop-back' test which tests the USB serial function independently from the AVR chip. In this day of $2 arduino nano cloned boards there is little reason to try and repair. Just try and learn what failed and try and not do that again.   

[Nusa]

The little USB serial things I got have enough pins, three are used with a jumper to set the 3.3/5v level. I was thinking of cutting the traces on two of those pins and solder bridge the traces to set the voltage. That would give me two extra pins on the existing header. Worthy of a thread maybe?

If you go that route, I'd suggest just reclaiming the VCC pin for DTR, leaving 5V and 3.3V outputs intact. Then add a tiny spdt microswitch on the back of the board to set the logic levels.

[james_s]

There is no isolation in the ESC in most cases. There are some "opto" ESCs which are supposed to have no BEC and optical isolation of the signal but quite a lot of "opto" ESCs have no optical isolation at all, the term has come to mean simply ESC with no BEC. The BEC makes good sense in the intended use, you plug the ESC into the main battery and that supplies power to your receiver and servos without the need to carry a separate receiver battery. I fly electric RC airplanes and mine all use the BEC to power the rest of the electronics.