Overview
Things
Story

Phase 1: STM32CubeMX Configuration
Phase 2: Hardware Setup in Breadboard
Phase 3: Executing the Code
Phase 4: Live Expressions and Gathering Data

Schematics
Code
Credits
Comments(0)

MICHAEL CADIZ

•

Paul Rodolf P. Castor

Published May 23, 2026

Coin Cell Voltage Monitor

Developing a range volt meter that uses an ADC.

IntermediateFull instructions provided4 hours39

Things used in this project

Hardware components

Coin Cell Battery CR2032

Breadboard (generic)

Jumper wires (generic)

Resistor 1M ohm

Story

The purpose of this experiment is to create a volt meter, where we will use an RT-Thread RT-Spark development board (STM32F407ZGT6) to measure how the CR2032 coin cell battery discharges.

Phase 1: STM32CubeMX Configuration

1.New Project: Open your STM32CubeMX and select the STM32F407ZGT6 as your target microcontroller.

2.Enable the ADC: Navigate to Analog then ADC1.

Check the box for IN2 (which corresponds to the PA2 pin you wired up).
Under ADC_Settings, set ClockPrescaler to PCLK2 divided by 8.
Ensure the Resolution is set to 12 bits (15 ADC Clock cycles)

3.Project Manager Settings:

Name your project in Project Manager tab.
Under Toolchain/IDE, select STM32CubeIDE.
Check the option to "Generate peripheral initialization as a pair of '.c/.h' files per peripheral".
Click Generate Code and then open the project in your standalone STM32CubeIDE application.

Phase 2: Hardware Setup in Breadboard

Connect a jumper wire from the positive (+) side of your external battery to the top leg of your R1 resistor on the breadboard (your "Battery/Source Voltage +" row).
Connect a jumper wire from the negative (-) side of your external battery to the Ground rail on your breadboard.
Keep the black jumper wire that connects the breadboard's ground to the RT-Spark's ground pin.
Connect the jumper wire in the middle of the two resistor to PA2 pin of RT-Spark.

Phase 3: Executing the Code

Open Core/Src/main.c. Scroll down to the USER CODE BEGIN PV section and add your variables.

Scroll down to your main() function. Inside the infinite while (1) loop, place your logic in the USER CODE BEGIN 3 section.

Phase 4: Live Expressions and Gathering Data

Compile and Launch: Click the Build (hammer) icon to compile. Once you see "0 errors", click the Debug (bug) icon to flash the code to the RT-Spark board.
Set Up the Tracker: When the debugger pauses at the start of main(), switch from the "Variables" tab to the Live Expressions tab. Add rawValue and voltage.
Run Real-Time: Click the Resume (Play) button in the top toolbar (or press F8).
Observe and Record: * The 0 values will instantly update to reflect the actual voltage passing through the breadboard.

Code

main.c

/* USER CODE BEGIN PV */
volatile uint16_t rawValue = 0;
volatile float sourceVoltage = 3.3;
volatile float halvedVoltage = 0;
volatile float voltage = 0;
/* USER CODE END PV */

////////////////////////////////////////////////////////////

/* USER CODE BEGIN 3 */
    HAL_ADC_Start(&hadc1);
    HAL_ADC_PollForConversion(&hadc1, 10);
    rawValue = HAL_ADC_GetValue(&hadc1);
    halvedVoltage = (rawValue * sourceVoltage) / 4095.0;
    voltage = halvedVoltage * 2;

    (void)voltage; 
}
/* USER CODE END 3 */

Credits

MICHAEL CADIZ

5 projects • 0 followers

Paul Rodolf P. Castor

21 projects • 9 followers

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Coin Cell Voltage Monitor

Coin Cell Voltage Monitor

Things used in this project

Hardware components

Story

Phase 1: STM32CubeMX Configuration

Phase 2: Hardware Setup in Breadboard

Phase 3: Executing the Code

Phase 4: Live Expressions and Gathering Data

Schematics

Pin Diagram

Code

main.c

Credits

MICHAEL CADIZ

Paul Rodolf P. Castor

Comments

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