Simple and Accurate LC Meter Circuit - 16F690

Digital LC Meter

A LCR meter [Inductance (L), Capacitance (C), and Resistance (R)] is a piece of electronic test equipment used to measure the inductance, capacitance and, resistance of a component. Inductance is the property of an electrical circuit causing voltage to be generated proportional to the rate of change in current in a circuit. In Electronics, capacitance is the ability of a body to hold an electrical charge. Capacitance is also a measure of the amount of electrical energy stored (or separated) for a given electric potential. The electrical resistance of an electrical element measures its opposition to the passage of an electric current. The meter reads L, C and R directly with no human calculation required.

Recently I found this LC meter project on internet and I was looking for that kind of project. Therefore, I build. Amazing it is work! Also the accuracy of this LC meter is great and it is very easy to build. So that, I post it here, because I think it is useful to you. You can visit original post from using this link: LMC3

The data below were determined based on theoretical calculations, the scale and the display automatically change.

	Min	Max	Resolution	Accuracy
Non Polar Condenser	1pF	1nF	0.1pF	1%
	1nF	100nF	1pF	1%
	100nF	1uF	1nF	2.5%
Electrolytic Capacitor	100nF	100,000uF	1nF	5%
Inductor	10nH	20H	10nH	5%
Resistance	1mΩ	0.5Ω	1mΩ	5%
Inductance	0.5Ω	30Ω	10mΩ	10%

Specifications of the LC Meter

LC Meter Diagram

LC Switch:
The purpose of this is, switch between inductance and capacitance mode. When you turn on the LC meter, you should set it to C mode.

Calibration Switch:
You can calibrate LC meter by pressing this. See Calibration for more details.

LC Meter Calibration

You have 3 modes to calibrate. When the process is completed, calibrated values are saving to the microcontroller’s internal EEPROM, so of course they are available after the re-start.

C Calibration

1. Switch on
2. Switch L/C switch to C position
3. Leave the test probes freely. Do not even touch it
4. Press and hold the CALIB button until the message Switch to meas. Then release the button
5. Wait for the appearance of 0.00 pF

L Calibration

1. Switch on
2. Switch to the L position
3. Connect L/C probe and GND probe together
4. Press and hold the CALIB button until the message Switch to meas. Then release the button
5. Wait for the appearance of 0.00 uH

ESR Calibration

1. Switch on
2. Switch to the C position
3. Connect LE probe and GND probe together
4. Press and hold the CALIB button until the message Switch to meas. Then release the button
5. Note the value shown on the screen

Calibration Values

• F0 = 499.9k
• Fcal = 355.9k

• Re = 180Ω

• Uesr0 = 58.3mV
• Fesr = 83.6k
• Rx = 0mΩ [-5mΩ to 5mΩ]

Critical Components

All the below resistors are 1%.
(In my circuit, I used normal resistors and those are measured using digital multimeter)

• 47Ω - R11
• 47kΩ - R8
• 100kΩ - R3-R5

• 1nF - C8, C11 (Polypropylene or Polyester)
• 33nF - C10 (Polypropylene 275V AC)
• 10uF - C7, C9 (Tantalum)

• 100uH - L1 (Low-loss DC resistance of 0.3-0.4Ω)

Testing

check 22pF ceramic capacitor

check 100uF electrolytic capacitor

check 100uH inductor

I was unable to find a reed relay, so I put 5v ordinary relay temporarily. In addition, my PCB designed for the TL2285 switches. But, I bought TL2230 by mistake :)

If the back-light brightness is low, you can increase back-light brightness by decreasing the value of the resistor R2 to 470Ω - 1k. You can change display contrast by adjusting 10k preset.
For PCB, Schematic and hex file, click download button.

You need to discharge capacitors properly before measuring.

LC Meter