Project Hub /Test & Measurement Instrumentation/Multimeters, Voltmeters & Ammeters/IndusVoltmeter: Smallest IoT Wireless Voltmeter with Wi-Fi

Intermediate

ESP32

Project Specific

3 – 6 Hours

Partial Kit

IndusVoltmeter: Smallest IoT Wireless Voltmeter with Wi-Fi

A miniature wireless IoT voltmeter built around the IndusBoard Coin (ESP32-S2) that measures voltage ranges of 0-3.3V and 0-24V and streams data to a web interface in real time.

Originally published on ElectronicsForU

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
0.96 Inch I2C/IIC 4pin OLED Display Module White Rs. 349.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: Other Dev Board (Indusboard / Maixduino / misc)
Diodes (1N4007 / 1N4148 / Schottky / Zener)
Thyristor / SCR / Triac / Varistor / Fuse
Capacitors

Browse all components

How It Works

The IndusVoltmeter functions as a compact, IoT-enabled measurement tool by combining onboard processing with precise analog voltage scaling. At its core, the IndusBoard Coin utilizing the ESP32-S2 microcontroller handles both data processing and wireless communication via Wi-Fi. Because the microcontroller's analog-to-digital converter pins are designed to read standard logic levels up to 3.3V, an external resistive voltage divider circuit is used to measure higher voltages safely. By pairing a 100kΩ resistor with a 15kΩ resistor, higher input voltages—up to a maximum of 24V—are scaled down proportionally so they fall within the safe operating range of the microcontroller's ADC pin. To protect the sensitive circuitry from unexpected electrical anomalies, a 1A fuse interrupts excessive current flow, a 1N4007 diode protects against reverse polarity connections, and a 0.1µF capacitor helps filter out high-frequency noise from the power supply for more stable readings. Once the analog voltage is sampled and converted into digital data by the ESP32-S2, the device hosts a local web server over Wi-Fi. This allows users to view real-time voltage measurements directly through a web interface on a computer or smartphone. Additionally, an optional OLED display can be attached to provide immediate local visual feedback of the measured values without needing to access the wireless network.

Why Build This

Develop a custom wireless measurement tool for on-site electronics troubleshooting and lab diagnostics without being tethered by physical wires.

Implement practical voltage scaling circuits using resistor dividers to safely interface high-voltage signals with microcontroller ADC inputs.

Stream live sensor and measurement data directly to a web-based interface for remote monitoring and data logging.

Real-World Application

On-site electronics troubleshooting, lab diagnostics, portable voltage monitoring, and quick electrical testing without physical proximity to the circuit.

Skills You'll Learn

Analog-to-digital conversion

Voltage divider design

Wi-Fi data streaming

Web server implementation on microcontrollers

Circuit protection and filtering

Safety Precautions

Ensure correct polarity when connecting power supplies to avoid damage, and do not exceed the maximum rated voltage input of 24V on the high-range circuit.

Technology Tags

IOT

WI-FI

VOLTMETER

ESP32-S2

ADC

VOLTAGE DIVIDER

OLED DISPLAY

WEB SERVER

Frequently Asked Questions

Can I measure voltages higher than 24V with this circuit?

No, the high-range circuit is specifically designed and calculated using the 100kΩ and 15kΩ resistors for a maximum limit of 24V. Exceeding this input can damage the microcontroller.

Is the OLED display strictly required for the voltmeter to work?

No, the OLED display is optional. The primary function of the IndusVoltmeter is to stream data wirelessly to a web interface, which can be viewed independently of the physical display.

What development environment should I use to program the ESP32-S2?

You can program the IndusBoard Coin using either the Arduino IDE or the standard ESP32 development environment by installing the appropriate board definitions.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

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