Project  # PE-09
Inductance / Capacitance Meter with LCD Display
 (using PIC 16F628)

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 Description

This LC meter may look simple but it is surprisingly accurate.

A handy tool for hobbyists to quickly check unknown capacitors & inductors.

Here we will focus mainly on the construction & selection of parts.

For the readers who are interested in the theory & design of the circuit, please refer to the following links.

Original author's & related links:


Schematic

 

CONSTRUCTION
<STEP-1> 

Solder the 16-pin (x1 row) pin header socket to the LCD display.

Make sure the socket is soldered on the correct side of the display board

Click on the picture below for a closer view

►

<STEP-2>  

insert -> solder -> trim leads
  Insert the components to the PCB then solder & trim the leads. Repeat this for a groups of 3~4 components at a time.
(do not trim the pins of relay, sockets, switches)

Start with the jumpers (4 pcs of different lengths) followed by the IC socket (with no IC on it).

Follow this sequence for the remaining parts :

*  the resistors
*  diodes (1N4148 &  D1)
*  4 MHz crystal
*  7805 reg. IC (horizontal mounting)
*  electrolytic capacitors (horizontal mounting)
*  ceramic capacitors
*  mylar capacitors (0.001uF, #102)
*  inductor (L), 100uH
*  reed relay
*  pin headers (6 pin x 1 row), 2 pcs  (for LCD display)
*  pin header  (4 pin x 2 row), 1 pc.   (calibration links)
*  switches, S1, S2, S3, S4
*  solder the 2-pin XH-254 connector base (for 9V battery)
*  trimmer pot. (VR1)

►

<STEP-3> 

Once the soldering work is completed you may proceed to :

  1. Insert the PIC microcontroller IC to the socket

  2. Insert the LCD display to the main board 

  3. Insert the 9V battery clip lead wires connector to  the PCB

 

TEST & CALIBRATION   (needs to be done only once)


1.  Set the mode switch (S1) to "up" position (capacitance measurement mode)
     Set the power switch (S3) to "OFF" position
     Set the "back light" switch (S2) to "ON" position

2.  Connect a 9V battery to the battery clip and turn ON the switch S3 to power up the LC meter

3.  If you see nothing on the display , try adjusting the Contrast trim-pot (VR1) . If it is set too far off, you will see nothing. The display should briefly show the word "Calibrating,..."  then C=0.0pF (or some other capacitance up to +/- 10pF ).

4. Allow several minutes "warm-up", then press the "zero" button to force a re-calibration. The display should now show C=0.0pF.

5. < Step 5 & 6  need to be done only for first time use. But need to redo if you replace the PIC  >
A "Sample" capacitor is provided for the calibration of the LC meter. The exact capacitance is written on the label pasted to the capacitor. It's somewhere near 5.6n (or 0.0056uF).

Insert the  "Sample" capacitor to the test terminals "Cx Lx" .  The LC meter should read somewhere near its value  (with up to +/- 10% error).

6. If the display does not tally with the capacitor's value, you can raise the reading by joining the links marked "4" on the diagram below. 
To lower the indicated capacitance, join the links marked "3" on the diagram below.
When the indicated value is "close enough" to the cap's value, the task is completed. The PIC will remember the calibration. So this is only needed to be done once..

7. The Inductance measuring function is automatically calibrated when you've calibrated the capacitance function. All the testing required is to check that the meter can be "zeroed" with the terminals shorted together.

  1. Check F2

     

  2. Check F1

     

  3. Lower C

     

  4. Raise C

 

 
** Please refer to Phil Rice's Home Page.  for a full description of calibration procedure under the title  " Calibration Instructions "

 

HOW TO USE

CAPACITANCE MEASUREMENT :    

1    Set the mode switch (S1) to "up" position 

2.   Switch on the meter (S3) & let the meter initialize  (the reading may not be zero).
      Wait for a few minutes for the PIC to stabilize & press S4 ( "zero") to recalibrate and check if the reading is near zero.
      If not zero then press S4 again
     
     
3.  Insert the capacitor to be measured at the terminal Cx Lx   (picture)

 

INDUCTANCE MEASUREMENT :

1    Set the mode switch (S1) to "up" position as in the case of capacitance measurement

2.   Switch on the meter (S3) & let the meter initialize  (the reading may not be zero).
      Wait for a few minutes for the PIC to stabilize & press S4 ( "zero") to recalibrate and check if the reading is near zero.
      If not zero then press S4 again

3.  Now set the mode switch (S1) to "down" position for inductance measurement
    
4.  Insert the coil/inductor to be measured at the terminal Cx Lx   (picture)
     If no inductor is inserted at the test terminals, the "over range" message will be displayed.
     Insert the inductor to be tested and read its value
 

 
PARTS LIST

1 -- PCB (Etched & drilled)

1 -- 1602 5V LCD display

1 -- 18 pin DIP socket
1 -- 16F628A PIC
   (pre-loaded with PIC codes)

1 -- Reed relay
    (# SIP-1A05) (tested)

1 -- C cal,  #102 (1000pF)

1 -- "Sample capacitor" for calibration

1 -- 100uH inductor, green
(brown-black-brown-silver)

1 -- 22uF 16V+ E cap

1 -- 1N400X
1 -- 1N4148
1 -- 7805 V. reg IC

2 -- 33P Ceramic cap

1 -- 104 Ceramic cap
1 -- 102 mylar / polyester capacitor
1 -- 150R 1/4W
1 -- 5K preset
1 -- 4 MHz crystal
       (low prof)


3 -- 10uF 6.3V+ E. cap
3 -- 100K 1/6W
3 -- 4K7 1/6W

4 -- 1K 1/6W
4 -- Jumpers

1 -- DPDT small push switch (momentary) 

1 -- DPDT push switch (latch)
(ALP, white/green)
 

1 -- matching knob for S1

2 -- PCB mt 2.54 SPDT slide switch

1 -- 4p x 2 row pin header

1 -- 16p x 1 row pin header socket
       (for LCD)

2 -- 6p x 1 row pin headers
      (for LCD )

2 -- Turn pin sockets, 3p x 1 row

1 -- 9V battery clip (to be soldered directly
      to the PCB)