ESP32 10mH Inductor Code: Building an LC Resonance Meter

If you are searching for 10mh inductor code, you are likely trying to measure an unknown or unmarked 10mH inductor using a microcontroller. You cannot "code" a passive inductor directly; instead, you write code to measure the resonant frequency of an LC (inductor-capacitor) tank circuit and calculate the inductance mathematically. For a 10mH inductor paired with a 100nF capacitor, the resonant frequency sits around 5 kHz—a perfect target for the ESP32’s hardware interrupts.

This guide provides the exact circuit theory, hardware spec sheet, and complete, compilable ESP32 C++ code to build a highly accurate LC resonance meter. We target the ESP32-WROOM-32 (30-pin DevKit V1) due to its 80 MHz clock speed and precise micros() timing resolution.

The Physics: LC Resonance and the 10mH Target

To measure inductance, we force the inductor and a known precision capacitor into a parallel resonant tank circuit. An LM393 comparator acts as an oscillator, sustaining the AC ringing. The ESP32 measures the time between zero-crossings (the period) to find the frequency.

The governing formula is derived from the resonant frequency equation:

f = 1 / (2π√(LC))
Rearranging to solve for Inductance (L):
L = 1 / (4π²f²C)

A 10mH (0.01 H) inductor is relatively large. In power electronics and audio crossovers, these components exhibit significant parasitic DC Resistance (DCR). If your 10mH inductor has a DCR above 50Ω, the Q-factor (Quality Factor) drops, and the LC tank will struggle to sustain a clean sine wave without aggressive positive feedback in the comparator circuit.

Hardware Spec Sheet & Pin Mapping

Before flashing the code, verify your components against this data-dense specification table. Using a ceramic capacitor instead of a film capacitor will introduce voltage coefficient errors, throwing off your 10mH calculation by up to 15%.

ESP32 Pin Mapping Table

The ESP32 10mH Inductor Code (C++)

The following code uses an Interrupt Service Routine (ISR) to capture the period between rising edges of the LM393 output. It includes timeout error handling to prevent the serial monitor from flooding when no inductor is connected.

#include <Arduino.h>
#include <math.h>

// PIN DEFINITIONS
const int SIGNAL_PIN = 15; // GPIO15 supports input, has pull-downs

// CONSTANTS
const float CAPACITANCE_FARADS = 100e-9; // 100nF precision film capacitor
const unsigned long TIMEOUT_US = 100000; // 100ms timeout for no-signal

volatile unsigned long lastMicros = 0;
volatile unsigned long periodUs = 0;
volatile bool newPeriodAvailable = false;

// ISR must be in IRAM for ESP32 to prevent cache faults during flash operations
void IRAM_ATTR isrCountPulse() {
  unsigned long currentMicros = micros();
  if (lastMicros != 0) {
    periodUs = currentMicros - lastMicros;
    newPeriodAvailable = true;
  }
  lastMicros = currentMicros;
}

void setup() {
  Serial.begin(115200);
  delay(1000); 
  Serial.println("ESP32 10mH Inductor LC Meter Initialized.");

  pinMode(SIGNAL_PIN, INPUT_PULLDOWN);
  attachInterrupt(digitalPinToInterrupt(SIGNAL_PIN), isrCountPulse, RISING);
}

void loop() {
  if (newPeriodAvailable) {
    newPeriodAvailable = false;
    if (periodUs > 0) {
      float frequencyHz = 1000000.0 / periodUs;
      
      // L = 1 / ( (2*pi*f)^2 * C )
      float omegaSq = pow(2.0 * PI * frequencyHz, 2);
      float inductanceHenries = 1.0 / (omegaSq * CAPACITANCE_FARADS);
      float inductanceMilliHenries = inductanceHenries * 1000.0;

      Serial.printf("Freq: %.2f Hz | Calculated L: %.3f mH\n", frequencyHz, inductanceMilliHenries);
    }
  }

  // Timeout handling for disconnected or shorted inductor
  static unsigned long lastCheck = millis();
  if (millis() - lastCheck > 500) {
    lastCheck = millis();
    if (!newPeriodAvailable && periodUs == 0) {
       Serial.println("Error: No oscillation detected. Check LC tank wiring or DCR.");
    }
  }
}

Debugging: Exact Errors and the "First Three Checks"

When adapting Arduino Uno interrupt code to the ESP32, developers frequently hit hardware-specific traps. If your build fails, here is how to diagnose it.

Common Compilation & Runtime Errors

1. Compilation Error: error: 'IRAM_ATTR' was not declared in this scope
Cause: You omitted the IRAM_ATTR tag before the ISR function, or you are compiling for an AVR board instead of ESP32. On the ESP32, ISRs must reside in Instruction RAM to execute while flash memory is being accessed (e.g., during WiFi operations).
Fix: Ensure void IRAM_ATTR isrCountPulse() is exactly as written, and verify the ESP32 board package is installed via the Boards Manager.

2. Runtime Error: Guru Meditation Error: Core 1 panic'ed (Interrupt wdt timeout on CPU1)
Cause: You added blocking code (like Serial.print() or delay()) inside the ISR. The ESP32's interrupt watchdog will reboot the chip if an ISR takes longer than a few microseconds.
Fix: Keep the ISR strictly to variable assignment (as shown in the code block). Process the data in the main loop().

The First Three Things to Check When It Fails to Read

If the serial monitor outputs "Error: No oscillation detected", do not rewrite the code. Check the physics and hardware in this exact order:

1. Measure the Inductor DCR: Use a multimeter to measure the DC resistance across the 10mH inductor. If it reads open (OL), the internal winding is broken. If it reads above 50Ω, the Q-factor is too low for the LM393 to sustain oscillation without a higher gain feedback resistor (change the 10kΩ pull-up to 4.7kΩ).
2. Probe the LM393 Output: Connect an oscilloscope or a multimeter set to AC Voltage across GPIO 15 and GND. You should see a ~1.5V AC signal (roughly 5 kHz). If you see 0V AC, the tank circuit is dead. Check that the capacitor is not shorted.
3. Verify GPIO Pin Constraints: Ensure you did not wire the LM393 output to GPIO 34, 35, 36, or 39. According to the Espressif ESP32 Datasheet, these pins are input-only and lack internal pull-up/pull-down resistors, which will cause the interrupt to float and fail to trigger cleanly.

Extending and Simplifying the Build

How to Extend: Auto-Ranging Capacitor Array

A 10mH inductor at 5 kHz is easy to measure. But what if you want to measure a 10µH RF choke? The frequency would spike to 159 kHz, pushing the limits of the LM393 and micros() resolution. To extend this build into a full LCR meter, add a CD4051 multiplexer IC to switch between a bank of capacitors (e.g., 1nF, 100nF, 10µF). The ESP32 can toggle the multiplexer via three digital pins, automatically selecting the capacitor that yields a frequency between 2 kHz and 20 kHz for optimal accuracy.

How to Simplify: The Off-The-Shelf Alternative

If you only need to measure a 10mH inductor once and do not want to breadboard a comparator circuit, bypass the embedded coding entirely. Purchase an LCR-T4 or TC1 Transistor Tester (typically $15–$25 on Amazon). These devices use an internal LM339 comparator and an ATmega328 running a pre-compiled discrete Fourier transform (DFT) algorithm to measure inductance, ESR, and capacitance simultaneously. However, for continuous logging, IoT integration, or custom manufacturing jigs, the ESP32 LC meter code provided above remains the superior, customizable choice.