Easy To Build DIY Digital Multimeter using Arduino to Test Voltage, Resistance, LED, Diode and Continuity

This DIY digital multimeter project functions by utilizing an Arduino Pro Micro microcontroller to process analog and digital signals measured from external circuits via four banana sockets. To measure DC voltage, the circuit uses a voltage divider network consisting of a 1K resistor, a 10K resistor, and two 4.7K resistors to step down the input potential safely within the microcontrollers analog-to-digital converter (ADC) acceptable input range. Resistance is measured by forming a voltage divider with a known reference resistor and reading the resulting voltage drop across the unknown component. For continuity testing and diode or LED checks, the microcontroller applies a small forward bias current and monitors the voltage drop or triggers an active buzzer when a low-resistance path is detected. Power is supplied independently to the system using two 3.7V 300mA lithium batteries, regulated to a stable 5V operating voltage via an AMS1117-5.0 voltage regulator and controlled through a physical toggle switch. User interaction is handled locally via a push button, while real-time measurement values, text, and diagnostics are rendered visually using a compact 0.91-inch 128x32 OLED display communicating over standard protocols. All components are assembled onto a perf board and interconnected using wiring, while the microcontroller runs custom code compiled through the Arduino IDE utilizing the SPI, Wire, Adafruit GFX, and Adafruit SSD1306 libraries to manage display rendering and sensor logic.