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LC Meterlc meter

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                  Using PIC12F629 and LM311 as LC meter.
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LC Meter is a part of modular IRMeasure system.


Overview

This unit uses PIC12F629 to measure capacity and induction. Capacity and induction is measured indirectly based on oscillator frequency change. Such frequency is measured by PIC12F629 and is used to calculate value of L or C. The advantage of this design is that it can measure very small capacitors too (1 pF).

LC Meter - feature list

  • range C : 0,1 pF - 2 microF
  • range L : 0 mH - 2 H
  • powered by 9V battery ( 13 mA / 9V )
  • very small dimensions: 34 x 48 mm
 

Design principle

LC Meter consists of 2 functional parts: LC oscillator (vibrating on its own around 800 kHz) and Frequency Counter (which reads the frequency of the LC oscillator). 

lc meter blocks

Frequency Counter is connected to an IR Transmitter which sends measured data wirelessly to IRMeasure Receiver (which then forwards this data to the PC). 

After connecting a capacitor or a coil to the input of the LC Meter the frequency of the LC oscillator changes. This frequency decreases from 800 kHz to a lower value. Based on this difference the capacity of the capacitor or induction of the coil is calculated. Such value is then sent to the PC where it is displayed on the monitor. 

LC meter schematic

The oscillator using LM311 generates the frequency of around 800 kHz. It is a standard schematic. Such signal enters the PIC12F629 microprocessor which is working as Frequency Counter. 

Second PIC12F629 microprocessor is responsible for the entire communication with IRMeasure Receiver (which receives the measured data from LC Meter). Transmitting diode TL217 is used to transmit data wirelesly using IR light.

lc meter schematic

It is possible to configure the transmiting diode power (and thus the range/distance of data sent by the LC Meter) by using appropriate resistors. The distance is by default up to 4 meters. Transmitting power is optimized for low current consumption therefore a regular 9V battery can be used as a power source.

Calibration

For calibration of the LC Meter use one 1,5 nF capacitor with a 2 % tolerance. The higher the capacitor accuracy the higher the accuracy of measurements. The calibration is possible anytime while the IRMeasure PC application is running (the actual calibration is performed from the PC). The perform the calibration please right click with the mouse on the LC Meter picture in IRMeasure. The calibration is used to compensate the temperature instability of the LC oscillator.

LC meter enables you to measure even the smallest capacitors starting from 0,1 pF. A disadvantage of it is that it is only possible to measure capacitors up to a 2 uF level approximately. For measurements of large electrolytic capacitors will be new unit called C-meter. This one is going to be clever enough to measure even the largest capacitors. It is going to be fully compatible with current systems, of course. 

Induction measurements :

Induction measurements go the same way as capacity measurements. The inductor is connected to the LM311s input port and frequency changes are recorded. Data is stored on your PC and the software computes induction. This is how almost all LC meters work. 

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Measurement is the same as with another LC meter. Simply put C or L to input of LC meter and you see the value of inductance or capacity online. You can use 15 LC meter at the same time ( or 15 other units ). The IRMeasure allows it.
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LC meter - complette unit.    Dimensions 34 x 48 mm only.

frequency counter   frequency counter frequency counter

To display data on your monitor you need IRMeasure software.
If you has a question , please contact us.