Interfacing Arduino Nano and Sim800L with one step down LM2596

Hello, I'm a programmer but I'm new to electronics.

My project works fine but I need your advice on how to use only one step down to power both, the arduino nano (5v) and the SIM800L (4v) and also I need to know if my connections (resistors, etc.) are acceptable.

Here's a video of my question: Question Video

And here are the schematics of my project:

My project needs to work with 12V, since it will be connected to a house alarm battery.

Thank You!

The odds are high the Nano will work with 4 volts eliminating the second buck converter. Be sure to test it thoroughly. Be absolutely sure your grounds are good before powering anything. Check this link to find out why: In-Depth: Send Receive SMS & Call with SIM800L GSM Module & Arduino The SIM800L requires ~2 amps during transmit.