How to Build a Simple Arduino Battery Voltage Monitor for Under $5

Building a battery voltage monitor with an Arduino is an easy and inexpensive way to keep tabs on the health of a battery. With just a few basic electronic components, you can assemble a simple circuit that will allow an Arduino to accurately read and display the voltage of a battery. Here is a step-by-step guide on how to build your own Arduino battery monitor for under $5.

What You'll Need

To build the battery voltage monitor, you'll need just a few low-cost components:

• Arduino board - The heart of the project. An Arduino Uno, Nano, or Pro Mini will work.

• Voltage divider circuit - Two resistors that reduce the battery's voltage to a level the Arduino can handle.

• Zener diode - Protects the Arduino from overvoltage.

• LCD display - Shows the battery voltage. A basic 16x2 LCD display is perfect.

• Breadboard - Allows easy connection of the circuit without soldering.

• Jumper wires - For breadboard connections.

• 9V battery - The battery to monitor. A 9V alkaline battery is commonly used.

How It Works

The Arduino cannot directly handle the voltage of a typical 9V battery, which would damage its analog input pins. The voltage divider circuit reduces the 9V to a lower, safer voltage that the Arduino can read.

The voltage divider consists of two resistors in series. The voltage is divided between them in proportion to their resistance values. With proper resistor values, the voltage is reduced to under 5V at the point between the resistors.

A Zener diode connected to this point protects against overvoltage. If the voltage tries to exceed the Zener's breakdown voltage, the diode will conduct electricity to ground, limiting the voltage.

The Arduino reads this reduced voltage on one of its analog input pins and converts it to a number from 0 to 1023. By using the known resistor values, the Arduino can calculate the true battery voltage based on the reading.

Finally, the voltage value is displayed on the LCD. The LCD is connected to the Arduino via several digital pins.

Building the Circuit

Step 1 - Add the Voltage Divider

On a breadboard, connect two resistors in series - for example, a 10KΩ resistor and a 5.1KΩ resistor. Calculate the target output voltage based on your Arduino's limits. For an Arduino Uno or Nano with a 5V limit, 3.3V is a safe output voltage.

Step 2 - Connect the Zener Diode

Add the Zener diode across the lower resistor. A 3.3V Zener is a good value for protecting a 5V Arduino. The cathode (striped side) connects to the point between the resistors.

Step 3 - Connect the LCD and Arduino

Hook up the LCD to the Arduino as per the LCD datasheet. A common configuration uses digital pins 4-7. The LCD will later display the voltage value.

Step 4 - Connect the Analog Input

Use a jumper wire to connect the point between the resistors to an analog input pin on the Arduino. Analog pin A0 is commonly used.

Step 5 - Power the Circuit

Provide power to the voltage divider, Arduino, and LCD display. For testing, apply 7-12V to the divider circuit. The Arduino and LCD can be powered separately.

Load the Arduino Sketch

With the hardware built, it's time to program the Arduino. The complete code can be found in the link below, but these are the key points:

• Define the resistor values in the sketch
• Read the analog voltage pin
• Use the voltage divider formula to calculate battery voltage
• Print the voltage value to the LCD

Be sure to set your LCD's dimensions and pin numbers. Upload the code to your Arduino and open the serial monitor to see the voltage output.

Full Arduino Battery Monitor Code

With that, your simple Arduino battery voltage monitor is complete! The final cost should be well under $5 for the components. Now you can easily keep track of the battery level for your projects.