Something in a complex project keeps on bricking my unos.... i figure putting 220ohm resistors in series from MCU out to project would prevent it. Its a lot of solderering, is this the best approach? Its usually the VR that blows, usually smoking... maybe just add them to a newer portion that brought the rash of problems?
Do you have a schematic of your connections to the Arduino?
You're likely drawing much more current out of the board than it was designed for.
The boards may not be bricked per se; you could probably replace the VRs and be up and running again...
But you have to fix your wiring first.
Hi, Some helpful info on the power issues here:
https://arduinoinfo.mywikis.net/wiki/ArduinoBoardDetails#Power_Considerations:
Thanks TerryKing, I am powering by means of 12vDC that literally comes out of the wall out of a maglock unit PSU. I didn't think how higher the voltage would eat up how much current it would handle.
I think I will switch my 5v bus (which powers basically a LCD 16x2) to a 5V outboard regulator (I got a bunch) and run that into the Vin at a much more sedate 5V so the MCU can power three LEDs as well off the pins. Maybe I don't need all those resistors! The varaible VReg then can run off the 12VDC.
I don't have a schematic online but I have a generic block diagram here:
As you see I plan to break off the LCD 16x2 from MCUs 5V out to the vVregs 5v set output. I also will power the arduino from 5v as well so it can safely power LEDs and such.
Old Setup:
[12v PSU]--->[MCU]5v--->[LCD 16x2]
| <==>[2 Reeds], [2 relay modules] [1 connection to maglock PCB],
|<=====> [3 LEDs], [ipCamera Relay Out]
NEW PLAN:
[12vPSU]-->[vVreg*]-->[MCU]<==>[2 Reeds], [2 relay modules] [1 connection to maglock PCB],
| <=====> [3 LEDs], [ipCamera Relay Out]
------> [5V Bus]---> [LCD 16x2]
Blackfin:
Do you have a schematic of your connections to the Arduino?You're likely drawing much more current out of the board than it was designed for.
The boards may not be bricked per se; you could probably replace the VRs and be up and running again...
But you have to fix your wiring first.
To my best knowledge a bad VR may still upload fine via USB as it doesn't depend on the VR, therefore a upload error may indicate a worse prognosis than just bad VR. Am I correct? Last one got bad checksums (verification error, first mismatch at byte 0x0000, 0xff != 0x0c). I do have a small pile of 'bad' UNOs that I'd love to see work again.
Hold on!
If you are trying to power a "standard" UNO with 12 V to the "barrel jack" or "Vin" you are already on a losing streak. The Arduinos were never designed to power other devices from the "5 V pin" except to a limited extent (500 mA) if powered through the USB jack.
If you are connecting anything else - displays, relay boards, whatever - let alone more than one, you need a switchmode regulator module to provide 5 V power to the 5 V pin. These are readily and cheaply available on eBay and such. It is unfortunate that you did not realise this to start with as it may delay your project, but it should have been part of your planning.
It is likely that the only part that has failed in your UNOs is the regulator, in which case simply remove the regulator and test it plugged in to the USB port. If it then works, fine; it is simply foolish to attempt to replace a regulator which is useless anyway.
The exception to this is a modernised "clone" of the UNO such as the "RoboRed", the product of Terry King who posted above. This is in fact, a substantially upgraded version of the "UNO SMD" - the processor chip is not replaceable (because - you should never have a reason to do so 
) with a proper switchmode regulator on board which can be used to power other 5 V modules.
mattlogue:
Something in a complex project keeps on bricking my unos.... i figure putting 220ohm resistors in series from MCU out to project would prevent it. Its a lot of solderering, is this the best approach?
The best approach is to post a complete schematic of your project for proper suggestions on what could be causing this.
Smoke usually means there's something fundamentally wrong with your approach, and without knowing what (that 12V supply is of course highly suspect - you're dropping 7V on your regulator, that's a lot of heat there and then) your proposed solution of just slapping on a few resistors is probably the wrong one, and on top of that you're going to keep making the same mistake again.