This tutorial teaches how you can build DIY PC based LCR meter to measure resistance, capacitance and inductance. Using PC as LCR meter is useful and if you don't have LCR meter or oscilloscope. LCR meter are quite expensive so here an alternative LCR meter presented. Resistance and capacitance can be measured using less expensive digital multimeter but it cannot measure inductance of an inductor. A DIY inductance meter with Arduino and LM393 was presented in previous article and here another simple technique to measure inductance is shown. The method here relies on PC soundcard. In the test that was conductance this PC LCR meter measured the resistance and capacitance to very close value. The inductance was also pretty close. This PC LCR meter requires just few components which are 1k potentiometer, 10kOhm resistor and two male to male audio jacks. It requires software which is free to download and it is very easy to setup. This PC LCR meter will be helpful to new comers in electronics circuit beginners and others will find this alternative technique knowledgeable.
How PC LCR meter works
LCR(Inductance Capacitance Resistance) is electronics circuit device that is used to measure inductance of an inductor, capacitance of a capacitor or the resistance of a resistor. This method relies on the fact that we can use voltage divider circuit to determine the impedance of the device under test(DUT). DUT is the resistor, inductor or capacitor whose value you want to determine. The the voltage divider circuit is made of a known value resistor and the unknown DUT. Then using PC we can send in known ac signal of known frequency and using line in input on the PC we can measure the voltages across the voltage divider network and the voltage across the DUT. Then using the value obtained we determine the impedance of the DUT.
Hardware and Circuit Diagram
The following picture shows the DIY PC LCR meter circuit build on a breadboard.
The above picture also shows how the speaker and line in audio jack is connected to the LCR meter on the breadboard.
The following is the circuit diagram.for making the PC LCR meter is shown below.
In the circuit schematic diagram, the resistor R1 of 10KOhm must be accurate measured resistor because the LCR meter software relies mainly on the accuracy of this resistor. The 1KOhm potentiometer is to calibrate or adjust the speaker output and line in input signal level.In the place labelled DUT, the component, resistor, capacitor or inductor is placed.
One may also place a 1uF(non-electrolytic) capacitor at the line in signal input as shown in the circuit drawing below. The 1uF capacitor is DC blocking and coupling capacitors.The speaker and the audio jack wire length should be not long and the short circuit wire needed during calibration should also be very short.
The implementation of the circuit without capacitor should also work because the PC soundcard has capacitors built into it.
Download Install Free PC LCR Software
The software that you will need is called the RCL-meter which is free of use and you can download from the following link:
http://www.rcl-meter.strobbe.org
but i think the download link dead so you can download it from the link below instead.
Download Install Free PC LCR Software
This pages describes how the LCR meter works and also has setup guide. At the end of the page you can find the program download link.
Note that once you have downloaded it and installed it do not immediately run it because it will output loud and high frequency sound from the speaker.
After you have downloaded and installed it. First build the circuit and plug in the speaker and line in audio jacks into the PC sockets. After that start the software. When you start the software starts you should see a message that ask the sound speaker output and input application that you want to use. Select the appropriate ones and then click ok. Then it says that you should keep the connection between the terminals of the DUT open so leave it open.
Now we have to perform diagnostics and calibration. Click on the diagnostics button to adjust the level. Click on the level 80% button. Then perform the following to set the level to 80%.
1. Open circuit the DUT connection and adjust the potentiometer such that the right input level is at 70%.
2. Short circuit the DUT connection and check if the right level is below 60%.
3. Open circuit the DUT connection and click on high freq. button(11025 Hz).
4. Adjust the potentiometer if the right input level is over 80 % or below 60 %.
5. Short circuit the DUT connection and check if the right level is below 60%.
6. Change input to low freq.( 980 Hz ) and repeat from step(1) to step (5).
You can repeat this and try to find potentiometer setting such that the input level is between 80 % and 60 %. Once done click on stop.
Next click on calibrate button and follow the instruction presented by the software. This is automatic step just open circuit click continue, short circuit and click continue. Then finally select the type of component(DUT) you want to measure and the result will be shown.
The following block diagram outlines the above steps:
PC LCR Test Result
Below are some test results.
Resistor value test and result
A test on 470KOhm (+-10% rated) test is shown.
Capacitor value test and result
Capacitor used is 10nF rated capacitor.
Inductor value test and result
A 22uH inductor was tested.
Video Demonstration of PC LCR meter
The following video shows how to setup the DIY(Do It Yourself) PC LCR meter, how use the use the LCR meter and to test the DUT components.
LCR meter uses is immensely important for electronics circuit designers and engineers. So this DIY PC LCR will be helpful to electronics engineering students, physics students, electronics hobbyist and to others as well.
Electronics testing instruments are tools which you need while working with electronics circuits. Some other useful instruments you can use at home are as follows.
- High Frequency Counter with Arduino
- Arduino 8MHz Signal Generator with ISR
