Self-contained Arduino LC Meter with Internal Calibration

Introduction:

When I set out to measure inductances using an Arduino, I found that existing methods were either overcomplicated (requiring an external shield) or cumbersome and inaccurate (using an external comparator). Additionally, these methods were limited in their ability to measure capacitances within a wide range.

To solve this problem, I decided to create my own LC meter using an Arduino and only passive external components. By combining the "Two Pin" capacitance tester with RobotZer0's idea of using the internal comparator, I was able to develop a truly self-contained LC meter with internal calibration and autoranging capability.

Features:

My code improves upon existing methods by adding rudimentary autoranging, internal calibration/zeroing of the test capacitance, low pass filtering, and integration averaging. These features improve the accuracy of the measurement by reducing statistical noise and increasing the precision by removing the offset component from capacitance measurement.

Known Issues:

The capacitance value for the frequency counter needs to be as precisely valued as possible for accuarate results. If the capacitance indicator displays an exclamation mark, the measurement may be innacurate due to a high resonance frequency, consider using a larger capacitor value to slow down the resonance frequency to enable more precise measurements.

Future Plans:

While I aim to keep this project as barebones as possible for easy implementation, I plan to create a second code file in the future that includes more advanced features. These may include more advanced reference calibration capability (utilizing newtonian or other polynomial weight functions which will be stored in the EEPROM and can be called by a smart calibration function) and support for LCDs. Additionally, I plan to implement the ability to measure ESR of a capacitor directly.

Instructions:

To wire the barebones configuration of the LC meter, connect the following pins:

Pin 11: Pulse pin
Pin 7: GND reference for internal comparator
Pin 6: HIGH input for internal comparator
Pin A5: Mode Selection pin
Pin A2: Autoranging Capacitor Positive test pin
Pin A0: Autoranging Capacitor Negative pin

Additionally:

Connect Pin 11 to a generic fast-ish diode (such as the BA159 or any other similar diode) in series with a 220 Ohm-ish resistor to limit current. This will be connected to the LC circuit with an unknown inductance and known capacitance.
Connect the ground and high pins of the comparator through a precision 47 kOhm resistor or potentiometer tuned to this value. This setup offers an improvement over other designs as it provides the ability for external hardware calibration.
Connect Pin 7 to the ground reference for the internal comparator, and connect Pin 6 to the HIGH input for the internal comparator.
Connect Pin A5 to the mode selection pin.
Connect Pin A2 to the capacitor positive test pin, and Pin A0 to the capacitor negative pin.