6 Channel Voltmeter

Some special applications often have to measure the voltage from several parts at the same time for example electronics repair, scientific and experimental purposes. if you're building a battery pack it can also show the voltage of each cell simultaneously.

In this project, we are making a 6-channel voltmeter that has 6 voltage dividers and an OLED screen that will show the reading from the different voltage channels. All of this is controlled by Seeed Studio XIAO SAMD21

1* Seeed Studio XIAO SAMD21

1* 0.91in 128x32 OLED screen 

6* 100K 0805 SMD

6* 22K 0805 SMD

6* 2 pin Hedderpins male and female

Cables

Heat shrinking tube

Xiao only can measure the voltage up to 3.3v more than that will damage the MCU, so we need to use a voltage divider for that. As the name suggests, a voltage divider will help us to divide higher voltage into smaller voltage which can be measured using Xiao. We are using 100k and 22k resistors to build our voltage divider with this we can measure up to 0v to 18v. More than this limit will fry your MCU.

So we just need 6 voltage dividers and 6 outputs that are connected to the GPIOs of the xiao. I designed the circuit and PCB EasyEDA then I exported the Gerber file from it 

I used SeeedStudio Fusion service for ordering his PCB, it turned out to be better than I expected

Seeed Fusion offers one-stop prototyping for PCB manufacture and PCB assembly, and as a result, they produce superior-quality PCBs and fast-turnkey PCBA within 7 working days.

Pcb assembly was straightforward. I just used my soldering iron to solder all the components. It was easy to solder the wire terminals, xiao, and OLED. 

Upload this code to Xiao using Arduino IDE

#include <SPI.h>

#include <Wire.h>

#include <Adafruit_GFX.h>

#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128 // OLED display width, in pixels

#define SCREEN_HEIGHT 64 // OLED display height, in pixels

#define OLED_RESET     -1 // Reset pin # (or -1 if sharing Arduino reset pin)

#define SCREEN_ADDRESS 0x3C ///< See datasheet for Address; 0x3D for 128x64, 0x3C for 128x32

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);


const int voltagePin[] = {A0, A1, A2, A3, A6, A7};

const int numChannels = 6;

const float R1 = 100000.0; // 100k ohms

const float R2 = 22500.0;  // 22k ohms


void setup() {

  Serial.begin(9600);

  // SSD1306_SWITCHCAPVCC = generate display voltage from 3.3V internally

  if(!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {

    Serial.println(F("SSD1306 allocation failed"));

    for(;;); // Don't proceed, loop forever

}

  display.clearDisplay();

  }


void loop() {

  display.clearDisplay();


  for (int i = 0; i < numChannels; i++) {

    float rawValue = analogRead(voltagePin[i]);

    float voltage = (rawValue / 1023.0) * 3.3; // Convert to voltage (assuming 3.3V reference)


    // Apply voltage divider formula

    voltage = voltage * (R1 + R2) / R2;


    display.setTextSize(1);

    display.setTextColor(SSD1306_WHITE);

    display.setCursor(0, i * 10);

    display.print("Channel ");

    display.print(i + 1);

    display.print(": ");

    display.print(voltage, 2);

    display.println(" V");

  }


  display.display();

  delay(300); // Adjust the delay based on your desired refresh rate

}

Now we need to make a connection wire for the voltage input we just need to solder 2 wires into a 2-pin male header pin and use a heat shrink for securing the wire in place 

I just connected these connection wires to the battery

And connected the header pin into the channel 1. Always make sure the polarity is correct

Well it is a super basic project but useful . if you have any deviation in the reading change the resistance value in the code.