Monitor Your Car Battery: Code & Setup

Wemos D1 Mini

Resistors

Wemos D1 Mini Power Shield

Having the ability to monitor your car battery can prevent some unpleasant surprises. I will show you how I assembled the hardware, loaded the software and installed the monitor in my car. I will be using the ESP8266 Board called Wemos D1 Mini.New to ESP8266? Watch my <a href="https://youtu.be/dGrJi-ebZgI">Introduction to ESP8266</a> video first.<h3 >Video Summary</h3><div class="se-component se-video-container __se__float-none" contenteditable="false" style="width: 100%;"><figure style="width: 100%; height: 56.25%; padding-bottom: 56.25%; margin: 0px;"><iframe frameborder="0" allowfullscreen="" src="https://www.youtube.com/embed/VnGRFwDrLHo" data-proportion="true" data-percentage="100%,56.25%" data-size="100%,56.25%" data-align="none" style="width: 100%; height: 100%;" data-index="0" data-file-size="0" data-origin="100%,56.25%"></iframe></figure></div>You will need a wemos d1 mini, a power shield and some resistors. First, I started by removing the power plug and installed the smaller connector to make the hardware more compact.<figure><img src=https://projects.arduinocontent.cc/33561a6c-e352-4da1-8f2c-642b78367b58.png /><figcaption> </figcaption></figure>The D1 mini can measure external voltage up to 3.3v by using a voltage divider using R1=220KΩ &amp; 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. To do that we can add another 1.22MΩ in series to get the total 1.44MΩ. I did this by soldering a 1MΩ resistor to a 220KΩ resistor as shown here.<figure><img src=https://projects.arduinocontent.cc/430bb82a-f683-4942-a0c9-967541f68ff9.png /><figcaption> </figcaption></figure>I attached a long wire to the power input terminals to be able to connect them to the car battery.<figure><img src=https://projects.arduinocontent.cc/77e1ad86-8868-48d0-8da0-b8c11776e88b.png /><figcaption> </figcaption></figure>I then connected the D1 mini to my laptop and load the software. Make sure you select the sensor.bin version for the Analog input functionality. I then resumed with a typical Tasmota configuration.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.<figure><img src=https://projects.arduinocontent.cc/0c3cf004-01ed-4faa-a117-dc628218c656.png /><figcaption> </figcaption></figure>I first wrapped the device in heat resistant tape to cover any exported pin to withstand the engine heat. Since the entire car chase is ground, I found the nearest screw and connected my ground to it. Next, I located the nearest connection to the battery positive rail and connected my positive power input to it.<figure><img src=https://projects.arduinocontent.cc/a41da2af-f065-4036-948e-44a77f8450a0.png /><figcaption> </figcaption></figure>I then proceeded with calibrating the range of the analog input. I did this by connecting a multimeter to the battery and read the current voltage (in my case it was 12.73 volts). I then did some trial and error until my reading was 1273 as the analog reading. The last step was closing the fuse box and the car hood.<figure><img src=https://projects.arduinocontent.cc/5aa29480-efc3-461b-acb0-7f6bb553dad9.png /><figcaption> </figcaption></figure>Back in Home Assistant, I opened the configuration file and added a new MQTT sensor - the code is attached above.<figure><img src=https://projects.arduinocontent.cc/31d95e52-517a-46b7-ad2b-c4295201f942.png /><figcaption> </figcaption></figure>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.The integration is now complete. You can now use this sensor to trigger alerts!If you found this useful, please consider subscribing to <a href="https://www.youtube.com/c/MrDIYca">my YouTube channel</a>.If you are interested in supporting my work, please visit <a href="https://www.mrdiy.ca/#support">this page</a>.

Monitor Your Car Battery: Code & Setup

This is how I monitor my car battery remotely over Wifi using this DIY device costing only couple of dollars.