FS: Custom "Arduino UNO" compatible boards designed and mfg. by me.

[RogueBotix]

I decided to re-design the Arduino uno board. I made a few design changes such as changing the usb chip so the board works well with USB 3. I also switch to a different regulator circuit so that the Arduino can happily run in a 24volt system. As well as a few other minor layout changes such as moving the pin 13 led and rx/tx right in front of their respective place on the header. The board uses high quality ceramic decoupling capacitors, so there are no electrolytics to dry out, and the board is assembled with eutectic lead solder, so it will not be subject to all the short comings of lead free solder such as: tin whiskers and mechanical fatigue.

I wanted to sell a high quality board, that was made in the USA, and would last virtually forever. I decided I should do all the production myself. I bought a Quad IVc pick and place, and a MiniPak wave soldering machine. So they were designed and assembled by me.

I am trying to sell them on ebay. currently I am selling them for the same price as the Adafruit boards. Please give me feedback, and if you would like, buy a board

https://www.ebay.com/itm/292886783729

Thank you so much

[sokoloff]

You probably need at least 29V and ideally 32V max input voltage to use on 24V (automotive, trucking, airplane) systems.

In any case, 26V is definitely not high enough for a charging lead acid battery of 12 cells, which is the overwhelmingly common 24V case.

[RogueBotix]

The regulator is designed for 24v systems, it has a 40v operating limit.

[mbest]

Could use another photo towards the connectors on the end.

[RogueBotix]

The USB and power jack? They are standard from a normal Arduino, but I will definitely add a picture tomorrow. Thank you for your feedback.

[janoc]

Careful about calling it "Arduino". That is trademarked and the Arduino AG will go after you for trademark infringement once they catch the wind of this. They are known for enforcing their marks.

The design of Arduinos is fair game but not the name. That's why Sparkfun calls theirs "Redboard" and Adafruit sells "MetroX" boards, even though they are clones of Arduino Uno.

[sokoloff]

The regulator is designed for 24v systems, it has a 40v operating limit.

That's great!!

Your Ebay listing though, says:

Using a higher quaility USB chip this will have better support for US 3.0, up to 26 volts input, allowing this to be used in a 24 volt system.

Typo on quality, USB, and suggests a spec of 26V upper limit.

[RogueBotix]

I didn't actually put Arduino on the board it self, I have however been putting it in the titles. What do you suggest I put in the title? Would it be ok if I put "Clone" After the word Arduino? Thanks for your feedback!

[RogueBotix]

The regulator is designed for 24v systems, it has a 40v operating limit.

That's great!!

Your Ebay listing though, says:

Using a higher quaility USB chip this will have better support for US 3.0, up to 26 volts input, allowing this to be used in a 24 volt system.

Typo on quality, USB, and suggests a spec of 26V upper limit.

Thank you so much! I observed your suggestion.

[RogueBotix]

I didn't actually put Arduino on the board it self, I have however been putting it in the titles. What do you suggest I put in the title? Would it be ok if I put "Clone" After the word Arduino? Thanks for your feedback!

Arduino-compatible is the proper verbiage AFAIK.

I Revised it. Thanks!

[janoc]

I didn't actually put Arduino on the board it self, I have however been putting it in the titles. What do you suggest I put in the title? Would it be ok if I put "Clone" After the word Arduino? Thanks for your feedback!

Arduino-compatible is the proper verbiage AFAIK.

I Revised it. Thanks!

Even better - create your own name for the boards. If it says only "Arduino-compatible", they could still send you a legal nastygram claiming that you are trying to profit from their trademark. If it says instead something like "SomeDuino 1 (compatible with Arduino Uno)" then you will likely be in the clear. I believe they even have a guide somewhere on their website that says what is OK and what is not with regards to the "Arduino" name and what you need to do if you want to make/sell own boards based on their designs.

EDIT: here it is: https://www.arduino.cc/en/Trademark/HomePage

   
    The product can't contain the name Arduino
    The board can't have Arduino written anywhere on it
    The board must not copy the Arduino Logo or graphic design
    The auction/website title can't use the Arduino name
    You can write in the description that the board is derived from Arduino.
    You must explicitly say that you're not connected to Arduino and your product is a derivative
    You must specify that any tech support request must be directed to you

So you must not put Arduino-compatible in the title but it may be in the description. Plus a few of the other formalities.

[Inverted18650]

Great idea and I will buy a couple to test in the 24V DIY BMS projects I have laying around. Nice work and thanks for sharing.

[Nusa]

If it's got a usb2 jack, in what way does it support usb3?

[RogueBotix]

If it's got a usb2 jack, in what way does it support usb3?

The Blue USB ports on computers are USB 3. These boards work with the USB 3.0 ports

[Nusa]

If it's got a usb2 jack, in what way does it support usb3?

The Blue USB ports on computers are USB 3. These boards work with the USB 3.0 ports

Meaning that some usb 3.0 implementations fucked up the 2.0 support? Haven't run into that problem personally.

Anyway, the way you have it worded now, wouldn't surprise me if someone returned it for not having a usb 3 port.

[sokoloff]

The regulator is designed for 24v systems, it has a 40v operating limit.

That's great!!

Your Ebay listing though, says:

Using a higher quaility USB chip this will have better support for US 3.0, up to 26 volts input, allowing this to be used in a 24 volt system.

Typo on quality, USB, and suggests a spec of 26V upper limit.

Thank you so much! I observed your suggestion.

It looks like the listing still suggests a 26V max input voltage at the top. That's not enough for a 24V vehicle (which runs at a nominal 28.8-ish volts).

If the actual limit is 40V, why not suggest that as a limit?

Similarly, listing still says "US 3.0, sporting a 26 volt upper limit", which I think should read "USB 3.0, sporting a 40 volt upper limit"

[Monkeh]

The regulator shown does not support 40V operation..

[Inverted18650]

The regulator shown does not support 40V operation..

Sure as hell doesn't. 26V continuous, 60V transient.

http://www.ti.com/lit/ds/symlink/lm2937.pdf

[retrolefty]

Interesting design. Using a switching regulator is a big improvement. I would have however preferred a USB micro or mini board connector, the old original USB connector is so big it sucks. I own probably 20 'arduino' boards using various AVR (168,328,1284, mega2560) chips mostly clones but a couple of real Arduino manufacture. However I never buy such a board that doesn't at least publish it's schematic. Doesn't have to be open sourced but a schematic drawing is  a must.

Do you have such a drawing to share? If not, why?


 

[RogueBotix]

Interesting design. Using a switching regulator is a big improvement. I would have however preferred a USB micro or mini board connector, the old original USB connector is so big it sucks. I own probably 20 'arduino' boards using various AVR (168,328,1284, mega2560) chips mostly clones but a couple of real Arduino manufacture. However I never buy such a board that doesn't at least publish it's schematic. Doesn't have to be open sourced but a schematic drawing is  a must.

Do you have such a drawing to share? If not, why?

I'll publish the schematic, its on my computer at work.

[bitseeker]

Neat board. Seems to have generated a good bit of interest.

How is the regulator mounted to the PCB? Is that a rivet? If so, it'd be nice to be able to more easily replace the regulator in case of an "input accident".

Aesthetically, and perhaps even practically, it'd be beneficial to have pin 13's LED further from the connector like you did with the RX/TX ones. That way, its placement looks similar, the pin label can go back in line with its neighbors, and you can see the LED better from that side of the board. Not a big deal, but a nice tweak.

For the photos, consider using a clean background (e.g., simple sheet of white or gray paper would suffice).

[janoc]

   
    The product can't contain the name Arduino
    The board can't have Arduino written anywhere on it
    The board must not copy the Arduino Logo or graphic design
    The auction/website title can't use the Arduino name
    You can write in the description that the board is derived from Arduino.
    You must explicitly say that you're not connected to Arduino and your product is a derivative
    You must specify that any tech support request must be directed to you

Stuff them. Ask an IP lawyer, and check if their claims are legitimate or not.
IMHO, you infringe a trademark if you give any false sensation that your product it that trademarked product.
If you make it clear that it's compatible or derived, then you should be fine, regardless how they formulate their words in their trademark guidelines.
Adding a line declaring the trademark belongs to Arduino and your product is an imitate should keep you safe in court.

Why those requirement shouldn't be legitimate? What they are asking is completely reasonable, IMO. If you go to an IP lawyer with this you will only walk out $500 lighter for the "consultation" and still will have to do the above.

The first 4 items follow directly from the fact that "Arduino" and the logos are protected marks. That's the trademark law imposing this, they are only making it clear for you. The rest is theirs requirements - but you ignore them at your own peril, people got sued/had legal problems for less when it came to trademarks (Sparkfun and Fluke's yellow multimeters come to mind).

Your "stuff them" advice may work for someone in China but hardly for the OP who is in the US where Arduino has been suing people (and winning!) over their trademarks before.

Risking a lawsuit (or at the very least having the auction pulled and potentially account banned by eBay) over something as idiotic as putting the "Arduino compatible" in the title of an auction instead of the description is just that - idiotic. It also gives anyone who would want to attack the OP over this a rather big "stick" because they could claim the OP acted in bad faith when they ignored even these very basic demands.

[wraper]

If it's got a usb2 jack, in what way does it support usb3?

The Blue USB ports on computers are USB 3. These boards work with the USB 3.0 ports

Meaning that some usb 3.0 implementations fucked up the 2.0 support? Haven't run into that problem personally.

Anyway, the way you have it worded now, wouldn't surprise me if someone returned it for not having a usb 3 port.

More like something fucked up on both ends. Because those ports work with other USB2.0 devices just fine. And it's not like silabs chip supports USB3, it just doesn't fail to work properly. Also what I can say with certainty is that original Arduino UNO has fucked up USB shield and ESD protection schematic. Designed by some idiot. It's so bad that ESD protection is not only non functional but MCU data pins can be fried through this "protection" if ESD hits the shield .

[sokoloff]

   
    The product can't contain the name Arduino
    The board can't have Arduino written anywhere on it
    The board must not copy the Arduino Logo or graphic design
    The auction/website title can't use the Arduino name
    You can write in the description that the board is derived from Arduino.
    You must explicitly say that you're not connected to Arduino and your product is a derivative
    You must specify that any tech support request must be directed to you

Stuff them. Ask an IP lawyer, and check if their claims are legitimate or not.
IMHO, you infringe a trademark if you give any false sensation that your product it that trademarked product.
If you make it clear that it's compatible or derived, then you should be fine, regardless how they formulate their words in their trademark guidelines.
Adding a line declaring the trademark belongs to Arduino and your product is an imitate should keep you safe in court.

Why those requirement shouldn't be legitimate? What they are asking is completely reasonable, IMO. If you go to an IP lawyer with this you will only walk out $500 lighter for the "consultation" and still will have to do the above.

The first 4 items follow directly from the fact that "Arduino" and the logos are protected marks. That's the trademark law imposing this, they are only making it clear for you. The rest is theirs requirements - but you ignore them at your own peril, people got sued/had legal problems for less when it came to trademarks (Sparkfun and Fluke's yellow multimeters come to mind).

I'm not convinced that the word "Arduino" cannot appear in the title (in the form/context of "Arduino compatible") of an auction or web page.
I'm also not convinced that the last two items are absolutely mandatory in the form of compelled speech. (I agree that you can't suggest that you're part of Arduino project, but I would be willing to risk not saying that I wasn't part of it in every single piece of collateral.)

I read these list of requirements as "if you do these, we won't bother you", but not "if you fail to do any of these, we will both bother you and we will win".

[Nusa]

   
    The product can't contain the name Arduino
    The board can't have Arduino written anywhere on it
    The board must not copy the Arduino Logo or graphic design
    The auction/website title can't use the Arduino name
    You can write in the description that the board is derived from Arduino.
    You must explicitly say that you're not connected to Arduino and your product is a derivative
    You must specify that any tech support request must be directed to you

Stuff them. Ask an IP lawyer, and check if their claims are legitimate or not.
IMHO, you infringe a trademark if you give any false sensation that your product it that trademarked product.
If you make it clear that it's compatible or derived, then you should be fine, regardless how they formulate their words in their trademark guidelines.
Adding a line declaring the trademark belongs to Arduino and your product is an imitate should keep you safe in court.

Why those requirement shouldn't be legitimate? What they are asking is completely reasonable, IMO. If you go to an IP lawyer with this you will only walk out $500 lighter for the "consultation" and still will have to do the above.

The first 4 items follow directly from the fact that "Arduino" and the logos are protected marks. That's the trademark law imposing this, they are only making it clear for you. The rest is theirs requirements - but you ignore them at your own peril, people got sued/had legal problems for less when it came to trademarks (Sparkfun and Fluke's yellow multimeters come to mind).

Your "stuff them" advice may work for someone in China but hardly for the OP who is in the US where Arduino has been suing people (and winning!) over their trademarks before.

Risking a lawsuit (or at the very least having the auction pulled and potentially account banned by eBay) over something as idiotic as putting the "Arduino compatible" in the title of an auction instead of the description is just that - idiotic.

Y'all must have missed the lawsuit over the Arduino trademark a couple years back between Arduino LLC (arduino.cc) and Arduino SRL (arduino.org). They ended it by forming a merged holding company, but the fight lasted for years. Given that history, I suspect the current company is quite willing to defend the Arduino trademark. The hardware is open source, no problem there, but they DO own the name.

[wraper]

Risking a lawsuit (or at the very least having the auction pulled and potentially account banned by eBay) over something as idiotic as putting the "Arduino compatible" in the title of an auction instead of the description is just that - idiotic. It also gives anyone who would want to attack the OP over this a rather big "stick" because they could claim the OP acted in bad faith when they ignored even these very basic demands.

It's not idiotic. Omitting arduino from title will produce much less hits from search results. It's called nominative fair use. https://en.wikipedia.org/wiki/Nominative_use

[janoc]

It's not idiotic. Omitting arduino from title will produce much less hits from search results. It's called nominative fair use. https://en.wikipedia.org/wiki/Nominative_use

Sorry but nope. That is not fair use. You are literally exploiting someone else's reputation (= trademark) to sell your goods - i.e. exactly what the trademark is meant to prevent. That is why they make a distinction between putting the "Arduino compatible" in the title and in the description (the former not being OK, the latter yes).

The criteria for the nominative fair use are as follows:

The nominative use test essentially states that one party may use or refer to the trademark of another if:

    The product or service cannot be readily identified without using the trademark (e.g. trademark is descriptive of a person, place, or product attribute).
    The user only uses as much of the mark as is necessary for the identification (e.g. the words but not the font or symbol).
    The user does nothing to suggest sponsorship or endorsement by the trademark holder. This applies even if the nominative use is commercial, and the same test applies for metatags.

The first certainly isn't met and the second test maybe - even if the fonts aren't used, the word "Arduino" is trademarked by itself, not only when written in that specific font.

[wraper]

It's not idiotic. Omitting arduino from title will produce much less hits from search results. It's called nominative fair use. https://en.wikipedia.org/wiki/Nominative_use

Sorry but nope. That is not fair use. You are literally exploiting someone else's trademark to sell your goods - i.e. exactly what the trademark is meant to prevent.

Sorry but yes. It's fair use. Using it for commercial reason does not prevent it from being fair use.

The first 2 certainly aren't met.

They are, especially obvious for second.

[donotdespisethesnake]

Y'all must have missed the lawsuit over the Arduino trademark a couple years back between Arduino LLC (arduino.cc) and Arduino SRL (arduino.org). They ended it by forming a merged holding company, but the fight lasted for years. Given that history, I suspect the current company is quite willing to defend the Arduino trademark. The hardware is open source, no problem there, but they DO own the name.

That was completely different. It wasn't the original Arduino suing a cloner, it was the manufacturing arm of Arduino called Smart Projects which got sold to Federico Musto, who then renamed the company to "Arduino SRL" claimed exclusive manufacturing and sales rights to Arduino branded products, and sued the original Arduino designers (Arduino LLC). https://en.wikipedia.org/wiki/Arduino#Trademark_dispute

In fact, Arduino have never sued any cloners, although they did bitch quite a lot in the early days, they don't like it but are pretty resigned to it.

As for not being able to use the word "Arduino" in a a listing, that''s just bollocks. As long you
a) don't pass off your product as being made by Arduino
b) call it something like "AVR board, compatible with Arduino Uno"
c) ideally acknowledge the trademark "Arduino Uno is a trademark of Arduino AG"
you will be on perfectly legal grounds, and no one from Arduino legal reps are going to write nasty letters or get your listing pulled.

[MasterT]

High voltage input ( >12 V ) with linear regulator is a big mistake. I especially buy 7.5 V power supply for my projects, since arduino with a TFT / LCD shield is just overheating. I can't imagine arduino board is used w/o anything attached to it, and power dissipation could be a big problem.

[RogueBotix]

[/quote]
More like something fucked up on both ends. Because those ports work with other USB2.0 devices just fine. And it's not like silabs chip supports USB3, it just doesn't fail to work properly.

[/quote]

Do you think it is possible to add this kind of wordage in the description? Because thats what I was going for...  Its just a bit to verbose to put that in a title I have never had an Arduino work in usb 3 ports. And what inspired me to incorporate this is, one day my boss had bought and arduino and was just playing around with it, but was pissed off when it wouldn't work with his laptop that only had usb 3 ports.

[bitseeker]

Yeah, I've run into USB2 devices that don't like USB3 ports. It's unfortunate, but it's a thing.

[RogueBotix]

High voltage input ( >12 V ) with linear regulator is a big mistake. I especially buy 7.5 V power supply for my projects, since arduino with a TFT / LCD shield is just overheating. I can't imagine arduino board is used w/o anything attached to it, and power dissipation could be a big problem.

Its not a linear regulator. If I run the voltage all the way up. The current draw does not increase at all, so then there no heat to be dissipated, making the board very efficient with power draw. The Regulator's heat is dissipated by a large copper plane on top and bottom of the PCB. The is a large hole underneath the regulator that solderes it to the copper plane when it goes through wave soldering. I do this all the time for the company I work for (my day job as an engineer). Heat sinks are expensive, and if you have the board real-estate, I can  shave a ton of money off a board, saving them lots of money. You can also expose slits in the copper plane, so that when it gets soldered it creates "fins" made of solder.

[wraper]

High voltage input ( >12 V ) with linear regulator is a big mistake. I especially buy 7.5 V power supply for my projects, since arduino with a TFT / LCD shield is just overheating. I can't imagine arduino board is used w/o anything attached to it, and power dissipation could be a big problem.

Its not a linear regulator. If I run the voltage all the way up. The current draw does not increase at all, so then there no heat to be dissipated, making the board very efficient with power draw. The Regulator's heat is dissipated by a large copper plane on top and bottom of the PCB. The is a large hole underneath the regulator that solderes it to the copper plane when it goes through wave soldering. I do this all the time for the company I work for (my day job as an engineer). Heat sinks are expensive, and if you have the board real-estate, I can  shave a ton of money off a board, saving them lots of money. You can also expose slits in the copper plane, so that when it gets soldered it creates "fins" made of solder.

Yes it is linear regulator.

If I run the voltage all the way up. The current draw does not increase at all

Exactly what happens with linear regulator.

so then there no heat to be dissipated

There is. P=U*I. U (voltage drop over vreg) goes up and dissipated power goes up as well.

[RogueBotix]

Power draw is the same from 5 volts to 26 when I plug it in to my lab supply. That will not be the case on a 7805 for example.

[wraper]

Power draw is the same from 5 volts to 26 when I plug it in to my lab supply. That will not be the case on a 7805 for example.

Current remains the same. Power goes up! If it was buck converter, current would go down as input voltage increases.

That will not be the case on a 7805 for example.

Yes it will be the case with 7805. 

[RogueBotix]

Power draw is the same from 5 volts to 26 when I plug it in to my lab supply. That will not be the case on a 7805 for example.

Current remains the same. Power goes up! If it was buck converter, current would go down as input voltage increases.

That will not be the case on a 7805 for example.

Yes it will be the case with 7805. 

yup... You are a right, a VERY stupid mistake on my part..

[MasterT]

I can't see right now on the official arduino UNO tech specification page how much current it's allowable for user to take out from +5V connector, to power up external shields, sensors, lcd etc.  It was somewhere, 500 mA or so.
But if a your board is gonna be arduino compatible, there should be some "power budget", at least 100 mA (about nokia 5110 consumed with  back-light on).
Have a look at arduino DUE schematic, switching regulator, and "huge" amount  of current for external peripheral - 800 mA!
https://store.arduino.cc/usa/arduino-due

[Nusa]

I can't see right now on the official arduino UNO tech specification page how much current it's allowable for user to take out from +5V connector, to power up external shields, sensors, lcd etc.  It was somewhere, 500 mA or so.
But if a your board is gonna be arduino compatible, there should be some "power budget", at least 100 mA (about nokia 5110 consumed with  back-light on).
Have a look at arduino DUE schematic, switching regulator, and "huge" amount  of current for external peripheral - 800 mA!
https://store.arduino.cc/usa/arduino-due

UNO product: https://store.arduino.cc/usa/arduino-uno-rev3  I didn't bother with the text, I just looked at the schematic provided.

The regulator on the official product is: https://www.mouser.com/ds/2/308/NCP1117-D-81326.pdf , which can provide at least 1000 mA. More if the input voltage is at the lower end of the range. Note that most UNO clones use a different cheaper regulator (or in OP's case, upgraded one), so don't try to apply official specs to clones.

If you're powering the board from the USB port, then of course the USB 2.0 per-port spec of 500 mA applies. Some sources might do better than spec.

[PlainName]

As for not being able to use the word "Arduino" in a a listing, that''s just bollocks. As long you
[...]
you will be on perfectly legal grounds, and no one from Arduino legal reps are going to write nasty letters or get your listing pulled.

Surely it should be irrelevant whether it could be legally enforced or not. The fact is that the Arduino chaps have kindly given you a massive leg up at no cost to yourself, and the minimum you could do in gratitude is conform to their request. After all, no-one is forcing you to nick their design and trade on their name.

[macboy]

Two suggestions:
- Some other Uno clones have an extra row of holes next to the headers. Usually these are populated with 0.1" headers, which makes it easy to connect F-F "dupont" cables to sensors, or a convenient place to attach a scope or logic probe.  It is a nice thing that takes little board space and causes no routing grief.
- Some other Uno clones have the USB-serial IC's handshake signals brought onto un-populated 0.1" pads near the IC. This is useful for adding hardware handshaking to the serial communication (it's a trivial software change once the hardware is connected).

[RogueBotix]

I really should before I starting building these, asked the community what would be good things to add, and suggestions... 

[bitseeker]

Better late than never. I see a V2.0 in your future...

[wraper]

I personally would add ESD protection to USB and all MCU pins. Would make way harder to kill it, especially considering that most tinkerers don't really understand what they are doing. BTW it does not seem that you have proper circuit for USB/external power. It seems that attaching external power will result in outputting voltage to USB.

[RogueBotix]

As it is it cant put more than 5v into the usb with external power. Though if it were to be a problem I could add a steering diode. But if I starting adding tvs diodes to all of the micro's pins, that is gonna put this board in the spectrum of no one is gonna buy this.... As it is its hard to buy this when chineese arduinos are like 5$ I vowed to never buy one of those chineese arduinos again after my 3d printer's usb died partway into a 2 week print..

I guess the most economical esd protection I could do would be put spark gaps on the board, which would help, maybe... nothing protects the end user someone from just grabbing the whole board and zapping something....

[TK]

I noticed some LEDs on the RX / TX pins... you need to be careful as they can have some side effects.  RX / TX pins are not exclusively used for Serial, they should work as General I/O pins as well.

[RogueBotix]

I noticed some LEDs on the RX / TX pins... you need to be careful as they can have some side effects.  RX / TX pins are not exclusively used for Serial, they should work as General I/O pins as well.

Pin 13 also has an led on it, that is also a feature arduino has and it is not a problem.

[wraper]

As it is it cant put more than 5v into the usb with external power. Though if it were to be a problem I could add a steering diode. But if I starting adding tvs diodes to all of the micro's pins, that is gonna put this board in the spectrum of no one is gonna buy this.... As it is its hard to buy this when chineese arduinos are like 5$ I vowed to never buy one of those chineese arduinos again after my 3d printer's usb died partway into a 2 week print..

I guess the most economical esd protection I could do would be put spark gaps on the board, which would help, maybe... nothing protects the end user someone from just grabbing the whole board and zapping something....

Powering USB is big a problem. You may even fry USB port of computer. Adding ESD protection for all ports would cost around $ 0.50-0.70 in parts. It's not about simply zapping. It would protect against many wrong things connected to the pins which otherwise would fry MCU.

[wraper]

BTW if you are concerned about cost, you'd better change vreg to something cheaper. At least add proper circuit for usb power like in original arduino. Cheap vreg+proper circuit would still cost less than single LM2937.

[wraper]

About powering USB. Regardless of possible failures when computer is on, think what happens when computer is off. You will be dumping almost all of the current vreg outputs into USB port. Most likely there will be power switch/protection IC on +5V rail of usb. You will push current in reverse through that switch (body diode in mosfet).

[RogueBotix]

yes I get it.... there is some saving grace in that these all have a polyfuse on them. but yes I get it.

[m98]

What's going on with that layout? Only use 45° angles between traces and try to avoid unnecessary bends. The decoupling cap for U3 could also be closer. And having a good ground plane won't hurt.
If you want some inspiration for a robust Arduino, look there: https://www.rugged-circuits.com/microcontroller-boards/ruggeduino-et-extended-temperature-40c-85c

[RogueBotix]

there is a huge ground plane for the cp2102, there are vias going to the bottom