LC meter based on the Franclin oscillator

　      ―――I will make up LC meter by using Arduino. At first I will explain the origin of the circuit.

http://chitose6thplant.web.fc2.com/arduino/lcm/LCM_PCB.html

 1.    Preface　

Mr.C.S.Franclin who had worked for Marcorni company in England had discovered the Franclin oscillator.

This one is composed by the phase inverting amplifier (By the triode) with LC resonator.

To combine the MPU frequency counter with the Franclin oscillator we can get the unknown L or C value

by resolving the equation.

This idea had come from east German engineer of Dr.Hegewald.

(Please refer in detail for VK3BHR WEB site: ”https://sites.google.com/site/vk3bhr/home/lcm1/faq?pli=1”)

  

2. The method → Arduino sketch　　

   How to get the value of the unknown L or C is to resolve the equation of the frequency.

<![if !supportLists]>a.     <![endif]>Let to oscillate with the basic L1 and C1. Then get the oscillating frequency of F1.

<![if !supportLists]>b.     <![endif]>Adding the standard C2 with paralleled. Then get the oscillating frequency of F2.

C2 must be precise

<![if !supportLists]>c.     <![endif]>because it shall be the basic value for calculation.

<![if !supportLists]>d.     <![endif]>F1 and F2 are described with C1, C2, and L1,

F1=1／2＊π＊sqrt（C1＊L1）、F2=1／2*π*sqrt（（C1+C2）*L1）

 

d.   F1, F2, and C2 are known and get C1/L1 value by resolving two systems of equations

    At the result C1 and L1 are involved the parasitic portion of the real circuit.

This portion of a-d is calibration. C1 and L1 were calibrated by the precise C2 value.

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<![if !supportLists]>e.     <![endif]>Connect L2 series with L1 and get F31. Then L2 value by resolving the nest equation.  

  F31＝1／2*π*sqrt(C1*(L1＋L2))

Connect C3 paralleled with C2 and get F32. Then C3 value by resolving the nest equation.

F32=1／2*π*sqrt（（C1+C3）*L1）

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　Arduino is sharing frequency counting, changing connection of LC by relay,

calculation C orL value from frequencies, and display for LCD.

Please refer the sketch on the GITHUB..

 GITHUB

 3. Circuit　　

I’m using 74HCU04 for the Franclin oscillator circuit. 74HCU04 is not merely logic circuit

but high gain FETs with higher frequency responding.

The relay is used for L C changing because of higher insulation. The double pole double 

throw switch is charged on L or C mode change.

There is the circuit diagram below.

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4. PCB    2 layer 50x50mm   

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5. Parts

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 CPs are the aluminum capacitors. As C5 is the standard capacitor,

please select higher precise one. The 0.1u are the ceramic ones. 1000pF is the film type.

The resisters are 1/8W or smaller.

 

６．Assembling

a. At first the lower parts shall be soldered. R or C.

b. For 74HCU04 you shall prepare the IC socket.

Also Dupont pin headers are used for Arduino Nano.

c. The double pole double throw switch shall be connected the each pin to the pin.

Considering for the case, you shall use wire.

d. The i2c interface LCD shall be connected via 4 wires with 4 pins header.

e. I’m using the alligator mouth clips for measuring node.

7．Operation

To power from Arduino Nano USB port, it turns on and displays the banner.

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 Then turn on the switch to calibration position. Arduino is turning on the relay

and the standard capacitor of 1000pF is connected. She got F1 and F2.

The values of L1 and C1 are acquired. At this case C1 is 504pF and L1 is 20uF.

(Parts printed value is 470pF and 22uH each.)

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To measure the enamel wired inductance. The calculated value by using Nagaoka

 coefficient is 0.24uH forΦ5/L7-10ｔ。The measured value is 0.197uH.

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 Furthermore I measured the silvered mica 1pF capacitor. 

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The video for explaining the operation is below YOUTUBE.

https://youtu.be/LxzoExQPcYk:embed:cite

If you have question, don’t hesitate to send mail for “nobcha48 AT gmail.com”.

 

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