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Return to BlogAVR Microcontroller Based LC Meter
Posted Feb 09, 2012 at 2:17 pm
Figure 1
The project pertains to an LC meter based on the AVR microcontroller which calculates and displays L and C from oscillation frequency using reference components.
The design of the circuit includes no relays, no range switching, and a minimum of controls but it requires two precision components, a precision capacitor and a precision inductor. Only one precision component needs to be started, either the reference capacitor or the reference inductor and the other precision component can be selected or adjusted using this meter. A pocket calculator or spreadsheet is required to convert from frequency to inductance or capacitance.
An LC oscillator oscillates at the resonant frequency of a parallel LC resonant circuit. A precision capacitor is switched in to the circuit when measuring an inductor, and vice versa. The circuit is composed of a comparator-based oscillator, a microcontroller that measures the frequency and calculates the inductance or capacitance from the frequency, and a microcontroller that takes the output from the first controller to drive a LCD.
The oscillator is permanently mounted onto the front panel by virtue of its being soldered onto the banana plugs. The calculated inductance/capacitance is displayed on two-line LCD.
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2 years ago: Looking at the data on this LC bridge, and there seems to be no way resonant frequency, of an inductance, can be found. This is important in finding distributed capacitance.
Basically, if inductance can be found, using as low a frequency, as possible, and THEN finding self-resonance, the distributed capacitance can be calculated. This feature can be important, in some VLF and ELF circuits.
If I find a micro-processor design, with this feature, I will be interested, otherwise, the old-fashioned pen and calculator will remain my mainstay.