The D1 mini can measure external voltage up to 3.3v by using a voltage divider using R1=220KΩ & R2=100KΩ . This the voltage within the 0-1 Volt that the ADC can tolerate. To increase the 3.3v to 16v needed for the car battery, we need to increase R1 to 1.44MΩ. In this video tutorial, I show how to use a wemos d1 mini, a power shiled and some resistors to wirelessly monitor your car battery voltage and send the readings to Home Assistant over MQTT. Please check the video description for links for the D1 Mini Power shield I used. Having the ability to monitor your car battery can prevent some unpleasant surprises. I will show you how I assembled the D1 mini: Shield: 5V: Power Supply, 5V(max: 1A) GND: GND: wemos.cc Revision 14220f49. Built with Sphinx using a theme provided by Read the Docs. Read the Docs v The General Mobile Radio Service (GMRS) is a North American land-mobile FM UHF radio service designed for short-distance two-way communication. It requires a license in United States but can be used license-free in Canada. ----- "Information is power. But like all power, there are those who want to keep it for themselves." The charger claims to handle batteries with capacity from 4AH to 100AH, works from 100v-240v and has winter and summer modes as well as handling all the major types of lead-acid batteries. The unit weighs under 0.5Kg and measures a mere 22*11*4.5cm. Mine has a 2-pin EU plug, plastic construction and looks solid. One of the most used micrcontroller in my DIY projects is the ESP8266. But all ESP8266 boards like the ESP8266 NodeMCU or the WeMos D1 Mini have one mayor downside: They have only 1 analog input pin. But you can increase the number of analog inputs with an analog multiplexer. .

wemos d1 mini power requirements