In this Homebrew Workbench Roundtable, Tobias KK7BCO and I are joined by first-time guest Rishav, from Nepal, who recently completed his master’s degree with research focused on relative navigation between two spacecraft and is soon to continue his work as a researcher in spacecraft guidance, navigation, and control (GNC).
HECKT-DUINO is a homebrew Arduino-based LC meter that Tobias and Rishav have been collaborating on. The design traces its roots to Neil Heckt’s article, "Build this self-calibrating LC meter to measure capacitance and inductance," published in the June 1996 issue of "Electronics Now".
For this build, the software has been rewritten for the Arduino Pro Mini using the ATmega328P, with the aim of keeping the code open source, readable, and hackable. Rather than treating the instrument as a black box, the project makes both the hardware and software accessible to anyone who wants to understand how the meter actually works. Rishav walks through the analog circuitry in detail, breaking the design into its main subsystems: the power supply, LC tuned circuit, and relaxation oscillator. The discussion then follows the signal through the circuit and explains how the meter determines inductance and capacitance from changes in oscillation frequency.
A particularly clever part of Heckt’s design is its self-calibration method. By temporarily switching a known reference capacitor into the LC network and measuring the resulting change in frequency, the meter can determine the effective inductance and capacitance of the actual circuit. This means that stray inductance and capacitance present in the physical build are incorporated into the calibration rather than simply ignored.
We also discuss the practical build process, debugging the circuit one subsystem at a time, and why moving the firmware to an Arduino makes the project particularly attractive as a beginner-friendly homebrew instrument. The Arduino implementation makes the frequency measurement, calibration procedure, calculations, display handling, and measurement logic readily available for inspection and modification.
*A small note from Rishav:* I may have stumbled over a few things or not explained some of the technical details as clearly as I would have liked to. My apologies in advance if that happened. That said, I’ll make sure the project documentation makes up for it. The circuit, calculations, calibration method, and build process will all be explained much more clearly and carefully there. I hope you enjoy the podcast, and even better, I hope it inspires you to build your own LC meter!
GitHub repository and project documentation: https://github.com/mathmuggle/heckt
Rishav’s blog: https://mathmuggle.com/
Arduino PRO MINI: https://link.amazon/B02lyB8gf
FTDI programming board for Arduino: https://link.amazon/B0beQfhkc
Screen: https://link.amazon/B08cqbpM4
Any ATmega328P-based Arduino should work. The Pro Mini is particularly well suited to this build because it contains little more than the circuitry required to run the microcontroller, without the onboard USB programming hardware found on boards such as the Arduino Uno. This makes it inexpensive and compact for a permanent homebrew instrument, while using the same board also keeps the pinout consistent with the project documentation.
Note that all of these are available also on eBay and Aliexpress.
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