Help me finalize the electronic components of my low voltage disconnect

I’m building a 12v low voltage disconnect.

No screen on mine and hard coded disconnect/reconnect values. I have the code portion settled but I need guidance on any additional components I might need to use…

  • Do I need a current limiting resistor on the Arduino input? Anywhere else? It is an Adafruit Trinket Pro that accepts up to 16v so I’m just running it off the supply/input 12v power.

Any kind of capacitor anywhere for voltage smoothing?

  • I have the output connected to a 12v automative iso relay (100 ohm resistance) - If the Arduino is running and I disconnect the relay, the arduino resets; Why would that happen?

Also just looking for comments from the hive mind before I finalize this and solder it all to a real breadboard.

Fritzing diagram attached.

Post a decent hand drawn schematic instead.

Fritzing diagrams are almost always misleading and often incomprehensible. Avoid them.

Yours is no exception: what "NPN"?
What are the pin assignments of the unknown "NPN"?

If the Arduino is running and I disconnect the relay, the arduino resets; Why would that happen?

Voltage spike in the power line, because the relay is either not properly decoupled or lacks a flyback diode across the coil. You will eventually destroy the Arduino that way.

I can't draw one, but I can tidy up the actual schematic in Fritzing and post that later.

Basically, it's got a 47k/10k voltage divider that goes to pin A0. A6 pin goes to the mosfet source pin to turn it "on" / "off"

This is the mosfet data sheet
http://www.promelec.ru/pdf/STP36NF06.pdf

This is the mosfet data sheet

So, you deliberately misled us by choosing "NPN" as the component.

A6 pin goes to the mosfet source pin to turn it "on" / "off"

An extremely bad idea.

You are wasting your own as well as our time.

Added the diode (1n4001)

jremington:
So, you deliberately misled us by choosing "NPN" as the component.
An extremely bad idea.

You are wasting your own as well as our time.

Come on man, I am here to learn and ask questions. If I were the smartest person ever I wouldn't need to make a post and ask for commentary. I'm sorry I am wasting your time. You do not need to help if that is how you feel. I am here to learn. I am also bedridden so I'm trying to learn something new. Give me a break, no reason to be rude.

  • Added a flyback diode (1n4001)
  • Changed mosfet in diagram from NPN to PNP

Why is it an extremely bad idea to turn the mosfet off and on the way that I am?