Strav's blog

I've been working on a device that I can add to a car which will connect to Home Assistant / MQTT and allow me to determine whether a vehicle is at home/away as well as allow me to monitor the charge level of the battery.  Since we have a few cars, some are not driven frequently and if the battery levels drop too low, they won't start and if low enough, the battery can be damaged or even completely ruined.  I decided to try to design the circuit and have it created as an arduino D1 Mini 'hat' using EasyEDA to design the circuit and JLCBCB to create it.  Here is all the relevant information I've gathered for the project:

Optocoupler
NOTE: examine the pinout carefully - it's not arranged the way I would have expected...
Battery Voltage Measurement
4N25 Optocoupler: A Simple Application Circuit [With Example]
Detect car +12V using Arduino
Optocoupler with Arduino

Voltage Divider
Voltage Divider Calculator
How can I use a 12 V input on a digital Arduino pin?

EasyEDA/JLCPCB
JLCPCB
WEMOS D1 MINI SHIELD LAYOUT

Arduino
How To Read The ESP8266 A0 Pin with Arduino
I Made a Car Trip Tracker .... without using GPS
A Car Trip Tracker without a GPS module
Monitor your Car Battery Remotely using ESP8266
DIY: Monitor Your Car Battery: Code & Setup
Vehicle Presence Detection - Home Automation
MQTT Vehicle Presence
MQTT-Vehicle-Presence

Home Assistant
Monitor your car battery in Home Assistant

Current Sensor
INA219 Current Sensor with Arduino