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Paul Rodolf P. Castor

Published May 1, 2026

Simple Volt-Meter with RT-Spark (Spark-1)

A small range Volt-Meter with good accuracy, all done with a very minimal setup.

IntermediateProtip1 hour17

Simple Volt-Meter with RT-Spark (Spark-1)

Things used in this project

Hardware components

Jumper wires (generic)

They usually come in a pack, and we only need 4 wires.

Breadboard (generic)

Resistor 1M ohm

Used for the Voltage-Divider Circuit

RT-Spark (Spark-1) RT-Thread Development Board

Panasonic Coin Cell CR1220

Optional, used to prove that it is accurate and legit.

Voltmeter, DC Voltage

Voltmeter or Multimeter, anything that can read voltage to again, proving the program that it works.

Software apps and online services

RT-Thread STM32CubeIDE (V1.19.0)

Voltage Monitoring ADC (Program)

Story

INTRODUCTION

For this project, the goal is to create a very simple Volt-Meter, with at least good accuracy and to understand how Analog-to-Digital Converter (ADC) works. This uses an RT-Spark (Spark-1) Development Board from the RT-Thread company.

ANALOG-TO-DIGITAL CONVERTER (ADC)

ADC is type of peripheral device, meaning, a type of module/sub-system which has its own purpose, and is typically connected/integrated to the bigger system with the goal of converting an analog signal to digital signal, hence the name ADC.

For this scenario, the ADC is an integrated peripheral device of the RT-Spark (Spark-1) Development Board, which uses the STM32F407ZGT6 Microcontroller.

SETTING UP THE ADC

To start off, it is an advantage to know that the RT-Spark (Spark-1) has 4 dedicated converters, 3 technically the same with different channels, and one as Digital-to-Analog Convert (DAC). For this scenario, 1st ADC will be used for the sake of simplicity. The ADC digital value range is 0-4095, and you need to map the values to Voltage by code.

First, create a new STM32 Project, choose the STM32F407ZGT6 MCU, and let the default settings work by itself.

1 / 3 • New STM32 Project

Then, setup pin PA2 to use ADC Module 1 on channel 2, and generate the CubeMX code. Note, you do not need to touch the GPIO Configuration of pin PA2; simply, keep it on default settings.

1 / 3 • Set PA2 as ADC1_IN2 (ADC Module 1 - Channel 2), Clock Prescaler as divided by 8 to set the definition of a single tick as very large amount of cycles before it is considered as 1 tick, disabled continuous conversion mode because we will be checking manually, and not require super fast checking, Sampling time as 480 Cycles

INPUT CIRCUIT DIAGRAM

For this section, the idea of voltage-divider will be used for a few reasons. One is to prevent loading voltages and currents beyond the maximum/acceptable values of the RT-Spark's pins or else it'll break/blow up the board by halving what the input gets. 2nd is to reduce the amount of power usage from the battery when checking the voltage by lowering the current passing through.

Voltage-Divider Diagram for the Input, preventing high power usage just by checking the voltage of a battery/source voltage

Once done, update the code, then build and run. After that, access debugging mode instead of running the code to check the value of the rawValue variable.

STM32CubeIDE in Debugger Mode, and Variables Tab

ENHANCED VOLTAGE READING ACCURACY (OPTIONAL)

To further improve the voltage reading, simply measure the actual resistance of R1 and R2 using a multimeter that can achieve a resistance reading of 1MΩ, and use the following formula

Scale factor Formula

If your Multimeter is incapable of reading large resistance values, simply assume that you know the actual value of R1, and use this formula, leading back to the scale factor formula shown above

Code

int main(void)
{
  uint16_t rawValue = 0;
  float sourceVoltage = 3.3;
  float halvedVoltage = 0;
  float voltage = 0;

  while (1)
  {
	  HAL_ADC_Start(&hadc1);
	  HAL_ADC_PollForConversion(&hadc1, 10);
	  rawValue = HAL_ADC_GetValue(&hadc1);
	  halvedVoltage = (rawValue * sourceVoltage)/ 4095.0;
	  voltage = halvedVoltage * 2;
  }

}

int main(void)
{
  uint16_t rawValue = 0;
  float voltage = 0;
  float tempVal = 0;
  float avg = 0;

  while (1)
  {
	  for(int i = 0; i < 10; i++) {
		  HAL_ADC_Start(&hadc1);
		  HAL_ADC_PollForConversion(&hadc1, 10);

		  rawValue = HAL_ADC_GetValue(&hadc1);
		  voltage = (rawValue * "yourVoltageSourceValue ex. 3.337") / 4095.0;
		  voltage = voltage * "scalefactor";
		  tempVal = tempVal + voltage;
	  }

	  avg = tempVal / 10;
	  tempVal = 0;
  }
}

Credits

Kenneth

3 projects • 0 followers

Paul Rodolf P. Castor

18 projects • 9 followers

Simple Volt-Meter with RT-Spark (Spark-1)

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Pin Diagram

Code

Simple Code

Enhanced Code

Credits

Kenneth

Paul Rodolf P. Castor

Comments

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Simple Volt-Meter with RT-Spark (Spark-1)

Simple Volt-Meter with RT-Spark (Spark-1)

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Pin Diagram

Code

Simple Code

Enhanced Code

Credits

Kenneth

Paul Rodolf P. Castor

Comments

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