Summary of LC Resonant Frequency Meter using AVR microcontroller
This article describes a DIY inductance measurement circuit using an AT90S2313 microcontroller and an LM393 oscillator. Designed for measuring inductors in the hundreds of microhenries to several millihenry range, it operates at lower frequencies (down to 1 kHz) to avoid core losses associated with high-frequency square waves. The system connects to a two-line LCD via a serial interface powered by +8 volts, allowing comparisons with precision bridges.
Parts used in the LC Resonant Frequency Meter:
- 5 volt regulator
- LM393 oscillator
- 0.047 uf capacitor
- AT90S2313 microcontroller
- Serial connector
- Two-line LCD module
- AVRStudio assembly source code
- AVRStudio hex file
A well known L/C measurement circuit is pressed into service to make a bare bones measurement circuit.
Download the AVRStudio assembly source: lgm031227I.asm
Download the AVRStudio hex file: lgm031227.hex
Left-to-right: The 5 volt regulator, the LM393 oscillator (a 0.047 uf capacitor is mounted on the LC circuit connector), the AT90S2313, and the serial connector to the LCD module.
Recently, I have needed to measure inductances in the hundreds of microhenries to several millihenry range. Though I have a pretty good LRC meter and an excellent bridge on my workbench in Mesa, Arizona, I wanted to make these measurements in my home in Thailand, thus I decided to put something together. The RF Inductance meter on this website is good for low value rf inductors, but because of the way it works – putting a sharp-edged square wave through the inductor -its not suitable for inductors made with high permeability ferrites (Because of pulse shape distortion that results from high frequency losses in the core.) This meter operates at lower frequencies, and by careful selection of the resonating capacitor, the oscillator can be made to run anywhere from 100 kHz on down. This makes it possible to test near standard frequencies like 1 kHz and 400 Hz, to compare results with precision bridges.
- What is the primary purpose of this project?
To measure inductances ranging from hundreds of microhenries to several millihenries. - Can this meter test inductors made with high permeability ferrites?
Yes, because it operates at lower frequencies to avoid pulse shape distortion caused by high frequency losses. - How does the operating frequency compare to other meters?
This meter runs anywhere from 100 kHz down to near standard frequencies like 1 kHz and 400 Hz. - What microcontroller drives the serial terminal?
The AT90S2313 frequency meter drives a serial terminal with a 0 to 5 volt signal. - How is the LCD module powered?
The serial connector provides switched +8 volts to power the LCD and its interface. - What component is mounted on the LC circuit connector?
A 0.047 uf capacitor is mounted on the LC circuit connector. - Where was the firmware adapted from?
The firmware was adapted from the RS-232 Freq. Meter/Pulse Generator project. - Why is the RF Inductance meter not suitable for some inductors?
It puts a sharp-edged square wave through the inductor, causing pulse shape distortion in cores with high frequency losses.
