Monitor your Car Battery Remotely using ESP8266 (DIY Project #2)

Having the ability to monitor your car
battery can prevent some unpleasant surprises. In this video, I'll show you
how I assembled the hardware, loaded the software and installed it in my car. You
will need a Wemos D1 mini, its power shield and some resistors. First, I
started by removing the power plug. I installed the smaller connector to make
the hardware more compact. The d1 mini can measure external voltage
up to 3.3 volts by using a voltage divider using these are values, which
brings it within that 0 to 1 volt the ADC can tolerate. To increase the 3.3
to 16 volts, needed for the car battery, we need to increase our 1.44 for
MegaOhm. To do that, we can add another 1.22 MegaOhm in series to get the
total 1.4 4 MegaOhm. I did this by soldering a 1 MegaOhm resistor to a 220
KOhm resistor. I added shrink wrap and then connected one end to the
voltage input from the car and the other end to a zero as shown here.

I then connected the d1 mini to my
laptop to load the software. Make sure you pick the sensor bin version for the analog input functionality. I even resumed with the typical Tasmota setup. Before heading to the car, I attach a
long wire to the power input terminals to be able to connect them to the car
battery. At the car, I opened the hood and located
the fuse box. I found the fuse box to be a safe and secure place to install my
device. I first wrapped the device with heat resistant tape to cover any exposed


You need this kind of tape to stand the engine heat. Since the entire car's
chassis is ground I found the nearest screw and
connected my ground to it. I then located the nearest connection to the battery
positive rail and connected my positive power input to it I then proceeded by calibrating the
range of the analog input. I did this by connected a multimeter to the battery
and read the current voltage- in my case it was 12.73. To adjust the range
I used the AdcParam command. I then did some trial and error until my reading
was close to 12.73. Now it was time to close the fuse box
and the car hood. Back in home assistant, I opened the configuration file and
added a new mqtt sensor – the code is in the description below. After I saved, I
restarted home assistant for it to take effect. When it came back online, I added the new sensor to the dashboard. Now you can use the sensor to trigger any kind of
automation. I have it setup so it sends me an alert when the voltage drops below

I hope you found this video useful. Thank you for watching …. and I'll see you
in the next one.

As found on YouTube

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