lc meter capacimeter inductimeter circuit pic 16f84 auto range lcmeter

lc meter capacimeter inductimeter circuit pic 16f84 auto range lcmeter


The good and high precision capacitor meter (Capacimeter) inductor meter (inductimeter) auto range lc meter for pic 16f84 or pic 16f628 and display lcd by phill rice

Construction of an apparel that allows measure inductors (Inductimeter) and capacitors (Capacimeter), knower like LC meter, using PIC (16f84 or 16f628) and display marries in LCD.

Coil of 39uh be measured

Translated of the excellent project inductor and capacitor meter ( lcmeter ) of the Phil Rice


Image gallery

Specifications for the lc meter with pic

The measure reach: is from 0 to 800nF to capacitance and 0 to 10mH goes inductance.
Precision: is of ± 1%
Reading: 0 to 1000pF (1nF) in pF 1nF to 800nF in nF auto range (it range automatic)
Resolution: is of ± 0.1 pF and ± 10nH. Good to have in the supported.

As works the lc meter with pic 16f84 or 16f628

It use the comparator LM311 with positive feedback

working the an oscillator parallel LC with digital exit. L is the shock of 82 µH and C it is the capacitor of 1000 pF. The frequency therefore it is f1 = 550 kHz. The capacitor of value precise, (CCal) 1000 pF ±1%, is linked in parallel C through the relay. The new total capacity is 1000 + 1000(Ccal) = 2000 pF, and the new frequency is f2 = 394 kHz. It is not important that those frequencies plows exact, the one that imports is the relationship among them, that flows of the capacitor of precision of 1000 pF. The two frequencies plows measured by PIC, during the solemnity-calibration. The important is that if the capacitor of 1000 pF (Ccal) it is necessary, then only the value of L exists (the shock of 82 µH) and the value of C (the capacitor of 1000 pF) that can determines those two frequencies, not importing your absolute values exactly. it GAVE WAY PIC ” it DISCOVERS ” THE TRUE AND CORRECT VALUE OF THE SHOCK AND OF THE CAPACITOR OF 1000 PF, AND TENDS THAT IT CAN MEASURE THE CAPACITOR OR AN EXTERNAL INDUCTOR. The inductor in test is placed in series with the shock. The capacitor in test is placed in parallel to the of 1000 pF

To the accomplish the solemnity-calibration, the inductances and capacitances sponge of the spinning it plows absorbed in the calculation accomplished by PIC. The key CH3 makes ” to zero ” the suitable value in the display. it gave way, only the capacity or additional inductance of the component to be measured plows shown in the display.

Assembly for the digital inductimeter and capacimeter

The tolerance of the apparel depends on the capacitor Ccal 1000pF, that should be made of polystyrene (styroflex “) with tolerance of less for the 1%. Oh you ask, where I get the capacitor with that tolerance, easy, make the capacitors association to get the wanted capacity, goes that to it uses the borrowed commercial Capacimeter of it adds amigo selects the capacitors to be used in the circuit. IN MY PROTOTYPE I USED ONE WITH TOLERANCE OF 1% GOTTEN IN THE SCRAP, RARE THING. C2 (Cmed) doesn’t need to be I need, just it is necessary thermal stability. Therefore uses one of polystyrene, if it will it uses potter it you use NPO.

It goes the inductor I used of begin the shock of RF 82µH, however the measures were not firm, then I used the coil toroidal with 85 you exhale of thread 30 coiled AWG in nucleus of powder of iron.

Display lcd for the lcmeters project

It display can be any one pattern Hitachi 16×1, 16×2 or 8×2, If it will uses one that you have backlight, it should have attention goes the consumption of energy. That it will be very larger, being recommended to uses to 7805 to-220.

In my prototype, I used PIC 16f627 from block telephone abandoned and the display in an apparel of fax destroyed. Live la scrap.

The resistors of the circuit can be of tolerance of 5%, adds demanding ones they it lives it uses with tolerance of 1%.

how to program the pic for the circuit lcmeter

To program PIC is easy you need the closes recorder and of the program. The one that I used was the grabber PROPIC2 of the magazine Mecatronica fácil (portuguese) from saber electronic. and the program is IC-PROG.

How to test the circuit lcmeter

All weld the components in the plate, without PIC, measure the tension of the regulator to verify 5 volts ± 25%. Everything right terrifies the pin 18 of the socket of the PIC and verify the operation of the relay (you should hear the relay being worked). Place Display it ties the circuit and adjust the potentiometer goes the best contrast. Already place the PIC engraving with the program and if everything certain you have Lc to digital put. In marries it doesn’t work it inspects every circuit, display, PIC ,Chaves, spinning, etc.

It goes it presses zero. PIC will count the cycles of the oscillator goes 0.1 seconds and it will exhibit the result. Com the inductor of 82µH and the capacitor of 1000pF in the circuit (without any external component, any calibration capacitor) the oscillator will run the approximately 550KHz, and the display it will show about 55000.
If the frequency goes very high (above 655.350KHz) the display will show reach out. If the oscillator i not working it will be shown 0 in the display.
It goes better precision the frequency should be of 10 a 15% inferior of 655KHz. You can adjust the coil to get.
One according to jumper connects the calibration capacitor Ccal, the frequency now will be of 394KHz.
The third Jumper in the pin 10 of the PIC, allows to select the display of 8 x 2, the result it will be shown in two lines.

To measure Inductor l meter

Select L in the function key the display it will show ” reach ” out, that reason doesn’t have any connected inductor. Place the measure terminals in shorts and press zero. Now it i only to place the inductor and to read the result.

Coil of 39uh be measured

To Measure capacitor c meter

Select C in the function key the display it will show adds pF, it is the capacity residual (it sponges) of the spinning. Work the key “zero” goes the brief instant. The display now indicates 0 pF. Now it is only to place the capacitor to measure in the terminals and to read the result in the display.

Capacitor of 47 nF be measured

Outer function to lcmeters circuit

The apparel can be zeroed with components in the measure terminals. And in the components that will be tested the difference later it will be shown + – of the value of the original component.

Precision of the circuit lcmeter

It depends on the components used by the assembler, during the calibration of the apparel, mistakes depend on the components used in the tank (LC) of the circuit oscillator and in the standard capacitor Ccal 1000pF that should be of goes the attn least 1% of tolerance., if possible smaller. I got one with tolerance of 0,625%.

The ferrite coil is not adapted goes the circuit tank, the ideal is to it uses the nucleus of powder of iron. AND THE NUCLEUS OF POWDER-OF-IRON (MICROMETALS) T50-2, THE GALLEY OF THE RADIOAMATEURISM KNOWS THOSE TYPES OF COMPONENTS. Any sorts things out it uses a RF shock to test the circuit, later try to find an appropriate coil, measuring and removing turns of some inductor found in the scrap (TV, video, etc.).

Conclusion of the circuit lc meter

Inductor and capacitor need, digital and easy of operating. With the worst possible group of components you will get the tolerance of goes the attn least 3%, and if it have luck and to perfect the little, it will get to set up your equipment with tolerance of less of “1%”

Credits for lc meter

Images of my prototype working.

Source Code
Update version 2, no need LM311

Other languages

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  1. hi,

    maybe you can recomend me were i can find:
    Capacimeter, must read 20pf, 200pf, and 2000pfs. If it reads more, not a problem,but it must read these three ratings at least.