I am building a circuit that I have made several times before without problem. They have been working steadily for 4-6 years in an escape room but this time I am running into some severe problems that I can not figure out. Please help me figure out where to look?
The project is an escape room prop where seven pictures are placed on the correct places. I have 7 RFID modules, each connected to an Arduino Nano(I prefer this over wiring several on same arduino). The RFID modules are Vellemanns(Same as the types sold everywhere like ebay, amazon) and the Arduinos are genuine. They are wired together per their instructions(3.3v vcc etc.).
All nanos are grounded and powered from a 12V power supply. This
They are all connected through an output pin (D4 on all 7 of them) to D3-D9 on another Arduino nano(also powered and grounded from same source). When each of them has the correct rfid tag, they send a signal to this Nano. It reads all seven signals and once all of them are correct it opens a relay connected on D10.
Now for some weird, weird reason I keep burning out these Nanos randomly in random order. Suddenly one by one they will start lighting up all three on board leds and become crazy hot... Then they will short out and have no light..
I've checked the power supply with a voltmeter and it is a stable 11.66V, which I do not think should be sufficient to blow these nanos, and I measured with the voltmeter upon start up as well to eliminate the possibility of a sudden spike causing the problem...
What else should I check?
Oh, I noticed some of the arduinos that have burned did not have the ground wire sufficiently stuck into the Wago clamps(I could put my nail on it and push it further in). Could this have been the problem? :S They would still light up and work when only powered by the 12V?
I'm at my wits end here, people so I desperately need some help...
That's too much. Use a 7V supply instead. Normally the on-board 5V regulator should turn off when overloaded, but nowadays poorly cloned components can creep in everywhere.
I can not decipher the Nano schematics, there may exist a problem when both the supply and USB are connected.
Your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advice on) your project See About the Installation & Troubleshooting category.
I think you will find 50mA is all you can draw from the Nano 3V3 pin.
The RFID;
Can you please post a link to data/specs and where you purchased the RFID?
When your Nano dies, have you measured the 5V and 3V3 output pins on the controllers?
Do you have a DMM?
Measure the current on the 12V positive wire for each Nano.
Does this also when detecting a tag.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png? Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
Thanks.. Tom...
PS. We need all this information because we need to know as much about your project as you do, you have it in front of you we don't.
With 12volt on V-in you shouldn't draw any current from any pin.
Just using 12volt puts a classic Nano already in the danger zone.
The USB lead plugged into a 5volt cellphone charger with USB socket is a much safer solution.
You also mentioned 3.3volt. Is that for the RFID module.
Take care there. The 3.3volt rail of a classic Nano is 'stolen' from the USB<>Serial chip.
You can't draw more than about 30mA from that pin.
Leo..
There is also the issue that a nano can be damaged if it’s not powered and yet power is present on an I/O pin , this might happen due to the way your system is designed or from bad connections ( common when using DuPont type cables )
Mount your parts neatly on some form of board or in a box and used soldered or screwed connections
Note that clones may not be able to perform as well as genuine devices .
See 
