Started burning at 18V

[alfonsrv]

See title. I'm assuming the module that started burning is the step-down converter. Had 3x4 battery packs with 1,5V batteries connected in series.

Board gets quite hot overall even when running with 12V - probably due to the WiFi module and the small board not being able to dissipate heat.

Just wanted to bring it up, as I think it should be mentioned in the README.md - in case someone plans to build this to carry in e.g. their backpack.

[exploitagency]

I just saw this issue and I am so sorry this happened to you. It could have been due to the batteries that you chose when fully charged are actually higher than the nominal voltage. Lets say that they actually read 1.65v fully charged, well that additional .15v multiplied by your 12 batteries would mean an extra 1.8v input and you may have actually been running the voltage regulator with an input voltage of 19.8 volts when the 18v rating was an ABSOLUTE MAXIMUM. My prototype I designed could handle up to 24v using the original BOM but there was no benefit in range that I could notice when running the reader at those higher voltages. In the future go as low as possible.

Please don't take that as criticism or even me knowing what happened as it is just speculation. I am just glad that nothing worse occured. Regardless what the issue may have been thank you very much for bringing this to my attention and I have added a safety warning and downgraded the maximum voltage rating to 12v to hopefully prevent this from happening again with notes that adding a heatsink to the voltage regulator would be a good idea and to aim for even lower voltages. But hackers are going to hack and abuse the specs just like this device actually should technically use level shifters but it works without them so it was created to use as few components as possible in that spirit.

SAFETY: It has come to my attention that the voltage regulator used on the commercially available units that you may find for sale is different than the voltage regulator I originally chose for this project. Also due to global chip shortages and the possibility of manufacturers substituting components I am downgrading the absolute maximum voltage rating to 12v as in you may be stressing the unit to its limits at this voltage and extra care should be taken. Most of my smaller portable prototypes ran at around 9v(x6 AA Batteries) and I found this to be more than adequate, remember that you can always power your reader and the RFID-Tool unit separately if needed and I suggest supplying your project with the lowest possible voltage that you can get away with. In fact, I have found multiple readers that run just fine at less than the recommended voltage. Note that I did not notice a significant range increase in my original testing between supplying 12v and 24v to my reader(I do not recommend this as I tend to abuse the specs for what I am testing, and I was using a different voltage regulator in my prototype). Also be advised that most commonly used batteries produce more than the commonly stated nominal voltage at a full charge. It may also be a good idea to apply a heatsink to your voltage regulator especially if you notice that the unit runs hot at your chosen voltage. It is also never recommended to leave your device unattended. Please be safe and take all necessary safety precautions when testing your setup.

[SufficientRole6246]

Hey I just had the same thing happen! However I was hooked up to a benchtop power supply limited to 11.9V. I had the device in the field, on a system I confirmed was using 12V, but it was acting funny and boot looping so I took it to the bench, when i plugged it in I got smoke. On examination it had the exact same burn pattern as this. This burned part is the voltage regulator? Thinking of adding a heatsink to my other device, as well as the 2 I ordered to replaced the burned one.

[SufficientRole6246]

Also, I would be interested in replacing the voltage regulator on my device and seeing if it still works. Can you point me in the direction of the correct component to purchase?
Thanks

[exploitagency]

I hate to hear that and am sorry that it happened to you. Was it ever attached to higher voltage? Below is the part for the voltage regulator that was used in the prototype. Voltage Regulator LM1117 voltage 3.3V out; current 800mA; package sot223; Mouser Part # 926-LM1117MPX3.3NOPB Also using a low amperage fuse on at minimum the positive Vin line is highly recommended, using a fuse on every line including data shouldn't hurt anything and could help protect connected equipment. I will try to update the schematics soon to include the addition of an inline fuse as well as go through the pull requests.

[SufficientRole6246]

Thanks for the update.
Re the schematic - I feel like I looked thru the repo here for said document but I could not find it. Am I blind haha?

AFAIK not attached to a higher voltage. At one time it was mistakenly attached to the data lines hooked up to an REX motion sensor. I will make a note to check the voltage on those lines.

Another question for you - I have been searching around for answers and not finding anyone who knows enough. I have been playing with the device on an HID ProxPro and an ICT Vario Prox reader. The HID puts out understandable data. However the same device hooked up to the Vario is spitting out what appears to be random data. Eg one card from the HID reader puts out
26 bit card,18 bit preamble,Binary:000000100000000001 01000010110001001001000101,HEX:2005B1245
and this was confirmed with a Proxmark3
However the same card, run 2x with the Vario puts out
30 bit card,14 bit preamble,Binary:00000010000001 010000110110001001000100000101,HEX:2050D89105
33 bit card,11 bit preamble,Binary:00000010001 011000000101110000100010010000101,HEX:22C0B84485

and I can't seem to make sense of either scan. Same deal with various other cards, puts out understandable data from the HID confirmed with the Proxmark and then gibberish with the Vario. Any direction you can point me in?

[Einstein2150]

Same here. 13,8V input has something done with the voltage regulator. At the moment all pins of the regulator are shorted. I desolder it and check if the ESP is booting when I direct connect 3.3V to the Vin of the ESP. I hope he is still alive. If he is alive I will try to change it with this part: https://www.amazon.de/gp/product/B079Q4CH6N/ref=ox_sc_act_title_1?smid=A19GSHTT314PS3&psc=1 otherwise I have to change and reflash the whole ESP too ... :-/

[Einstein2150]

Same here. 13,8V input has something done with the voltage regulator. At the moment all pins of the regulator are shorted. I desolder it and check if the ESP is booting when I direct connect 3.3V to the Vin of the ESP. I hope he is still alive. If he is alive I will try to change it with this part: https://www.amazon.de/gp/product/B079Q4CH6N/ref=ox_sc_act_title_1?smid=A19GSHTT314PS3&psc=1 otherwise I have to change and reflash the whole ESP too ... :-/

Update: ESP is death too :-/