In this article we will give the most complete instructions that will allow you to make a capacitor capacitance meter with your own hands, without the help of qualified craftsmen.

Unfortunately, equipment often fails. There is most often one reason - the appearance of an electrolytic capacitor. All radio amateurs are familiar with the so-called “drying out”, which occurs due to a violation of the tightness of the device housing. Reactance increases due to a decrease in rated capacitance.

Further, during operation, electrochemical reactions begin to occur, they destroy the terminal joints. As a result, the contacts are broken, forming a contact resistance that sometimes amounts to tens of Ohms. The same thing will happen when a resistor is connected to the working capacitor. The presence of this same series resistance will negatively affect the operation of the electronic device; the entire operation of the capacitors in the circuit will be distorted.

Due to the strong influence of resistance in the range of three to five ohms, switching power supplies become unusable, because expensive transistors and microcircuits in them burn out. If the parts were checked during assembly of the device, and no errors were made during installation, then there will be no problems with its setup.

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Scheme, principle of operation, device

This circuit is used using an operational amplifier. The device that we are going to make with our own hands will allow us to measure the capacitance of capacitors in the range from a couple of picofarads to one microfarad.

Let's understand the given diagram:

• Subbands. The unit has 6 “subranges”, their high limits are 10, 100; 1000 pF, as well as 0.01, 0.1 and 1 µF. The capacitance is measured using the measuring grid of the microammeter.
• Purpose. The basis of the device's operation is the measurement of alternating current; it passes through the capacitor, which needs to be examined.
• The DA 1 amplifier contains a pulse generator. The oscillations of their repetition are subject to the capacitance C 1-C 6 of the capacitors, as well as the position of the toggle switch of the “tuning” resistor R 5. The frequency will be variable from 100 Hz to 200 kHz. We determine for the trimming resistor R 1 a commensurate model of oscillations at the output of the generator.
• The diodes indicated in the diagram, such as D 3 and D 6, resistors (adjusted) R 7-R 11, microammeter RA 1, make up the alternating current meter itself. Inside the microammeter, the resistance must be no more than 3 kOhm, so that the measurement error does not exceed ten percent on a range of up to 10 pF.
• Trimmer resistors R 7 - R 11 are connected to other subranges in parallel with P A 1. The desired measuring subrange is adjusted using the toggle switch S A 1. One category of contacts switches capacitors (frequency setting) C 1 and C 6 in the generator, the second switches resistors in the indicator.
• In order for the device to receive energy, it needs a 2-polar stabilized source (voltage from 8 to 15 V). The values ​​of the frequency-setting capacitor may vary by 20%, but they themselves must have high temporal and temperature stability.

Of course, for an ordinary person who does not understand physics, this may all seem complicated, but you must understand that in order to make a capacitor capacitance meter with your own hands, you need to have certain knowledge and skills. Next, let's talk about how to set up the device.

Setting up the measuring device

To make the correct adjustment, follow the instructions:

1. First, symmetry of oscillations is achieved using resistor R 1. The “slider” of resistor R 5 is in the middle.
2. The next step is to connect the 10 pf reference capacitor to the terminals marked cx. Using resistor R 5, move the microammeter needle to the corresponding scale of the capacitance of the reference capacitor.
3. Next, the oscillation shape at the output of the generator is checked. Calibration is carried out on all subranges; resistors R 7 and R 11 are used here.

The mechanism of the device may be different. Size parameters depend on the type of microammeter. There are no special features when working with the device.

Creating different meter models

AVR series model

You can make such a meter based on a variable transistor. Here are the instructions:

1. We select a contactor;
2. We measure the output voltage;
3. negative resistance in the capacitance meter is no more than 45 ohms;
4. If the conductivity is 40 microns, then the overload will be 4 Amperes;
5. To improve measurement accuracy, you need to use comparators;
6. There is also an opinion that it is better to use only open filters, since they are not afraid of impulse noise in case of heavy load;
7. It is also recommended to use pole stabilizers, but only grid comparators are not suitable for modifying the device;

Before turning on the capacitance meter, you need to measure the resistance, which should be approximately 40 ohms for well-made devices. But the indicator may differ, depending on the frequency of modification.

The module based on PIC16F628A can be of an adjustable type;

It is better not to install high conductivity filters;

Before we start soldering, we need to check the output voltage;

If the resistance is too high, then change the transistor;

We use comparators to overcome impulse noise;

Additionally we use conductor stabilizers;

The display can be text, which is the easiest and most convenient. They need to be installed through channel ports;

Next, using the tester, we set up the modification;

If the capacitance values ​​of the capacitors are too high, then we change transistors with low conductivity.

You can learn more about how to make a capacitor capacitance meter with your own hands from the video below.

Video instructions

A digital measuring device is now not uncommon in the laboratory of every radio amateur. But not all of them can measure the characteristics of capacitors. The meter, the electrical circuit of which is shown in the figure below, is specialized for measuring the capacitance of capacitors in four subranges:

• 0…0.01 microfarad;
• 0…0.1 microfarad;
• 0…1.0 microfarad;
• 0…10.0 microfarads.

A liquid crystal indicator of the IZHTs-5 brand is used as a display device. Basis of operation capacitor capacitance meter next:

A controlled low-frequency signal generator is assembled on radio elements DD1.1 and DD1.2, the operating frequency of which depends on the characteristics of external radio elements R2 - C4 (C1 - C3). The generator is controlled via pin 2 of DD1.1, to which the RC circuit is connected.

The measured capacitor Cx is connected to terminals X1 and when contacts 1 - 3 of the SB1 button are closed, it is first discharged, and then, when the SB1 button is released, it is charged from the Upit source. +9 V through one of the resistances R4-R7, depending on the selected subrange.

The charging time of the capacitance Cx specifies the moment of operation of the generator, that is, at its output (pin 4 DD1.2) a specific number of pulses will be generated, proportional to the capacitance Cx. These signals go to the input of a frequency meter assembled on counters DD2-DD5 of the K176IE4 brand. This microcircuit is a decade with the conversion of the counter code into the code of a seven-segment indicator.

The outputs of each chip DD2-DD5 are connected to the appropriate pins of the four-digit indicator HG1. For stable operation of the ILC-5 indicator, rectangular signals from the output of the generator using radio elements DD1.3, DD1.4 are supplied to its common electrode (pin 1, 34). The same signals go to pin 6 DD2-DD5 to control the output signals of the microcircuits (pin 17).

A generator based on radio elements DD6.1, DD6.2 forms the operating cycle of the device (1.5...2 s). When the generator output has a high voltage, capacitance C7 is charged through resistance R3 and a short positive signal is formed at pin 5 of DD2-DD6 - an electrical signal that resets the counters to zero.

Then press the SA1 “Measurement” button and the indicator displays the capacitance value of the capacitor Cx for 1.5...2 s. To control the accuracy of the capacitance meter, a reference capacitance C6 is included, which is connected to the meter input via switch SA1.

Setting up a capacitance meter

After installing the electrical circuit, Up is supplied to it. +9 V and test the performance of generators based on radio elements DD1.3, DD1.4 and DD6.1, DD6.2. If they are working properly, then the HG1 indicator will light up in all “O” digits. Next, pins 1, 2 of DD1.1 are connected to each other, as a result, signals should be generated at pins 4 of DD1.4 and the HG1 indication will change.

Test the functionality of the generator on all ranges, switching to them using switches SA2 - SA5. In the highest frequency range (on SA5), stable generation is achieved using a variable resistor R2. Following this, pins 1, 2 of DD1.1 are opened. connect a reference capacitance of 1000 pF to the Cx input, switch to the range “0...0.01 μm” and, after resetting the values ​​of the HG1 indicator, press and then release the SB1 “Measurement” button.

The indicator will display a certain value. By repeating the measurement steps with variable resistor R7, they achieve the display of “1000” on HG1. The electrical circuit can also be adjusted on other subranges, but other reference capacitances should be used (0.01 microfarad, 0.1 microfarad, 1.0 microfarad). After this, the adjustment of the capacitor capacitance meter can be considered complete.

Capacitor Capacitance Meter Parts

Containers C1 - C4, C6 must be metal film grades K71, K73, K77, K78. The 561LA7 microcircuit can be replaced with a 176LA7. In the role of IP, it is possible to use a Krona brand battery or a 7D - 0.1 battery or a mains power supply.

“Designs and technologies to help electronics lovers”, Elagin N.A.

Recently, in amateur radio and professional literature, a lot of attention has been paid to such devices as electrolytic capacitors. And it’s not surprising, because frequencies and powers are growing “before our eyes,” and these capacitors bear a huge responsibility for the performance of both individual components and the circuit as a whole.

I would like to warn you right away that most of the components and circuit solutions were gleaned from forums and magazines, so I do not claim any authorship on my part; on the contrary, I want to help novice repairmen figure out the endless circuits and variations of meters and probes. All the diagrams provided here have been assembled and tested more than once, and appropriate conclusions have been drawn regarding the operation of this or that design.

So, the first scheme, which has become almost a classic for beginner ESR Metrobuilders “Manfred” - this is how forum users kindly call it, after its creator, Manfred Ludens ludens.cl/Electron/esr/esr.html

It was repeated by hundreds, and maybe thousands of radio amateurs, and were mostly satisfied with the result. Its main advantage is a sequential measurement circuit, due to which the minimum ESR corresponds to the maximum voltage on the shunt resistor R6, which, in turn, has a beneficial effect on the operation of the detector diodes.

I did not repeat this scheme myself, but came to a similar one through trial and error. Among the disadvantages, we can note the “walking” of zero on temperature, and the dependence of the scale on the parameters of the diodes and op-amp. Increased supply voltage required for device operation. The sensitivity of the device can be easily increased by reducing resistors R5 and R6 to 1-2 ohms and, accordingly, increasing the gain of the op-amp; you may have to replace it with 2 higher speed ones.

My first EPS sampler, which still works well to this day.

The circuit has not been preserved, and one might say that it never existed; I collected from all over the world, bit by bit, what suited me from the circuit design, however, the following circuit from a radio magazine was taken as a basis:

The following changes have been made:

1. Powered by mobile phone lithium battery
2. The stabilizer is excluded, since the operating voltage limits of the Lithium Battery are quite narrow
3. Transformers TV1 TV2 are shunted with 10 and 100 Ohm resistors to reduce emissions when measuring small capacities
4. The output of 561ln2 was buffered by 2 complementary transistors.

In general, the device turned out like this:

After assembling and calibrating this device, 5 Meredian digital telephone sets, which had been lying in a box labeled “hopeless” for 6 years, were immediately repaired. Everyone in the department started making similar samples for themselves :).

For greater versatility, I added additional functions:

1. infrared radiation receiver, for visual and auditory testing of remote controls (a very popular function for TV repairs)
2. illumination of the place where the probes touch the capacitors
3. “vibrick” from a mobile phone, helps to localize bad soldering and microphone effects in details.

Remote control video

And recently on the “radiokot.ru” forum, Mr. Simurg posted an article dedicated to a similar device. In it, he used a low-voltage supply, a bridge measurement circuit, which made it possible to measure capacitors with ultra-low ESR levels.

His colleague RL55, taking the Simurg circuit as a basis, extremely simplified the device, according to his statements, without deteriorating the parameters. His diagram looks like this:

The device below, I had to assemble hastily, as they say, “out of necessity.” I was visiting relatives, and the TV there was broken and no one could repair it. Or rather, it was possible to repair it, but for no more than a week, the horizontal transistor was on all the time, there was no TV circuit. Then I remembered that I had seen a simple test kit on the forums, I remembered the circuit by heart, a relative was also a little involved in amateur radio, he “riveted” audio amplifiers, so all the parts were quickly found. A couple of hours of puffing with a soldering iron, and this little device was born:

In 5 minutes, 4 dried electrolytics were localized and replaced, which were determined by a multimeter to be normal, and a certain amount of the noble drink was drunk for success. After repair, the TV has been working properly for 4 years.

A device of this type has become like a panacea in difficult times when you don’t have a normal tester with you. It is assembled quickly, repairs are made, and finally it is solemnly presented to the owner as a souvenir, and “in case something happens.” After such a ceremony, the soul of the payer usually opens twice, or even three times wider :)

I wanted something synchronous, I started thinking about the implementation scheme, and now in the magazine “Radio 1 2011”, as if by magic, an article was published, I didn’t even have to think. I decided to check what kind of animal it was. I assembled it and it turned out like this:

The product did not cause any particular delight, it works almost like all the previous ones, there is, of course, a difference in the readings of 1-2 divisions, in certain cases. Maybe its readings are more reliable, but a probe is a probe, and this has almost no effect on the quality of defect detection. I also equipped it with an LED so that I could see “where are you putting it?”

In general, you can do repairs for the sake of your soul. And for accurate measurements, you need to look for a more solid ESR meter circuit.

Well, lastly, on the website monitor.net, member buratino posted a simple project on how you can make an ESR probe from an ordinary cheap digital multimeter. The project intrigued me so much that I decided to try it, and this is what came out of it.

The body is adapted from a marker

A capacitor is an element of an electrical circuit consisting of conducting electrodes (plates) separated by a dielectric. Designed to use its electrical capacity. A capacitor with a capacitance C, to which a voltage U is applied, accumulates a charge Q on one side and Q on the other. The capacitance here is in farads, the voltage is in volts, the charge is in coulombs. When a current of 1 A flows through a capacitor with a capacity of 1 F, the voltage changes by 1 V in 1 s.

One farad has a huge capacitance, so microfarads (µF) or picofarads (pF) are usually used. 1F = 106 µF = 109 nF = 1012 pF. In practice, values ​​ranging from a few picofarads to tens of thousands of microfarads are used. The charging current of a capacitor is different from the current through a resistor. It depends not on the magnitude of the voltage, but on the rate of change of the latter. For this reason, measuring capacitance requires special circuit solutions based on the characteristics of the capacitor.

Designations on capacitors

The easiest way to determine the capacitance value is by the markings on the capacitor body.

Electrolytic (oxide) polar capacitor with a capacity of 22000 µF, designed for a nominal voltage of 50 V DC. There is a designation WV - operating voltage. The marking of a non-polar capacitor must indicate the possibility of operation in high voltage alternating current circuits (220 VAC).

Film capacitor with a capacity of 330000 pF (0.33 µF). The value in this case is determined by the last digit of a three-digit number, indicating the number of zeros. The following letter indicates the permissible error, here - 5%. The third digit can be 8 or 9. Then the first two are multiplied by 0.01 or 0.1, respectively.

Capacitances up to 100 pF are marked, with rare exceptions, with the corresponding number. This is enough to obtain data about the product; the vast majority of capacitors are marked this way. The manufacturer can come up with his own unique designations, which are not always possible to decipher. This especially applies to the color code of domestic products. It is impossible to recognize the capacity by erased markings; in such a situation, you cannot do without measurements.

Calculations using electrical engineering formulas

The simplest RC circuit consists of a resistor and a capacitor connected in parallel.

After performing mathematical transformations (not given here), the properties of the circuit are determined, from which it follows that if a charged capacitor is connected to a resistor, it will discharge as shown in the graph.

The product RC is called the time constant of the circuit. When R is in ohms and C is in farads, the product RC corresponds to seconds. For a capacitance of 1 μF and a resistance of 1 kOhm, the time constant is 1 ms, if the capacitor was charged to a voltage of 1 V, when a resistor is connected, the current in the circuit will be 1 mA. When charging, the voltage across the capacitor will reach Vo in time t ≥ RC. In practice, the following rule applies: in a time of 5 RC, the capacitor will be charged or discharged by 99%. At other values, the voltage will change exponentially. At 2.2 RC it will be 90%, at 3 RC it will be 95%. This information is sufficient to calculate the capacity using simple devices.

Measuring circuit

To determine the capacitance of an unknown capacitor, you should include it in a circuit consisting of a resistor and a power source. The input voltage is selected slightly lower than the rated voltage of the capacitor; if it is unknown, 10–12 volts will be sufficient. You also need a stopwatch. To eliminate the influence of the internal resistance of the power source on the circuit parameters, a switch must be installed at the input.

The resistance is selected experimentally, more for the convenience of timing, in most cases within five to ten kiloohms. The voltage across the capacitor is monitored with a voltmeter. Time is counted from the moment the power is turned on - when charging and turning off, if the discharge is controlled. Having known resistance and time values, the capacitance is calculated using the formula t = RC.

It is more convenient to count the discharge time of the capacitor and mark the values ​​at 90% or 95% of the initial voltage; in this case, the calculation is carried out using the formulas 2.2t = 2.2RC and 3t = 3RC. In this way, you can find out the capacitance of electrolytic capacitors with an accuracy determined by the measurement errors of time, voltage and resistance. Using it for ceramic and other small capacitances, using a 50 Hz transformer and calculating capacitance, gives an unpredictable error.

Measuring instruments

The most accessible method for measuring capacitance is a widely used multimeter with this capability.

In most cases, such devices have an upper measurement limit of tens of microfarads, which is sufficient for standard applications. The reading error does not exceed 1% and is proportional to the capacity. To check, just insert the capacitor leads into the intended sockets and read the readings; the whole process takes a minimum of time. This function is not present in all models of multimeters, but it is often found with different measurement limits and methods of connecting the capacitor. To determine more detailed characteristics of the capacitor (loss tangent and others), other devices are used, designed for a specific task, often stationary devices.

The measurement circuit mainly implements the bridge method. They are used limitedly in special professional areas and are not widely used.

Homemade C-meter

Without taking into account various exotic solutions, such as a ballistic galvanometer and bridge circuits with a resistance store, a novice radio amateur can make a simple device or an attachment for a multimeter. The widely used 555 series chip is quite suitable for these purposes. This is a real-time timer with a built-in digital comparator, in this case used as a generator.

The frequency of rectangular pulses is set by selecting resistors R1–R8 and capacitors C1, C2 using switch SA1 and is equal to: 25 kHz, 2.5 kHz, 250 Hz, 25Hz - corresponding to switch positions 1, 2, 3 and 4–8. The capacitor Cx is charged at a pulse repetition rate through the diode VD1, to a fixed voltage. The discharge occurs during a pause through resistances R10, R12–R15. At this time, a pulse is formed with a duration depending on the capacitance Cx (the larger the capacitance, the longer the pulse). After passing through the integrating circuit R11 C3, a voltage appears at the output corresponding to the pulse length and proportional to the value of the capacitance Cx. A multimeter (X 1) is connected here to measure voltage at a limit of 200 mV. The positions of switch SA1 (starting from the first) correspond to the limits: 20 pF, 200 pF, 2 nF, 20 nF, 0.2 µF, 2 µF, 20 µF, 200 µF.

Adjustment of the structure must be done with a device that will be used in the future. Capacitors for adjustment must be selected with a capacity equal to the measurement subranges and as accurately as possible, the error will depend on this. Selected capacitors are connected one by one to X1. First of all, the subranges of 20 pF–20 nF are adjusted; for this, the corresponding trimming resistors R1, R3, R5, R7 are used to achieve the corresponding multimeter readings; you may have to slightly change the values ​​of the series-connected resistances. On other subranges (0.2 µF–200 µF) calibration is carried out with resistors R12–R15.

When choosing a power source, it should be taken into account that the amplitude of the pulses directly depends on its stability. Integrated stabilizers of the 78xx series are quite applicable here. The circuit consumes a current of no more than 20–30 milliamps and a filter capacitor with a capacity of 47–100 microfarads will be sufficient. The measurement error, if all conditions are met, can be about 5%; in the first and last subranges, due to the influence of the capacitance of the structure itself and the output resistance of the timer, it increases to 20%. This must be taken into account when working at extreme limits.

Construction and details

R1, R5 6.8k R12 12k R10 100k C1 47nF

R2, R6 51k R13 1.2k R11 100k C2 470pF

R3, R7 68k R14 120 C3 0.47mkF

R4, R8 510k R15 13

Diode VD1 - any low-power pulsed, film capacitors, with low leakage current. The microcircuit is any of the 555 series (LM555, NE555 and others), the Russian analogue is KR1006VI1. The meter can be almost any voltmeter with a high input impedance, which is calibrated for it. The power source must have an output of 5–15 volts at a current of 0.1 A. Stabilizers with a fixed voltage are suitable: 7805, 7809, 7812, 78Lxx.

PCB option and component layout

Video on the topic

This circuit, despite its apparent complexity, is quite simple to repeat, since it is assembled on digital microcircuits and, in the absence of errors in installation and the use of known-good parts, practically does not require adjustment. However, the capabilities of the device are quite large:

• measurement range – 0.01 – 10000 µF;
• 4 subranges – 10, 100, 1000, 10,000 µF;
• sub-range selection – automatic;
• result indication – digital, 4 digits with floating decimal point;
• measurement error – least significant unit;

Let's look at the device diagram:

click to enlarge

On the DD1 chip, or more precisely on two of its elements, a quartz oscillator is assembled, the operation of which requires no explanation. Next, the clock frequency is sent to a divider assembled on DD2 – DD4 microcircuits. Signals from it with frequencies of 1,000, 100, 10 and 1 kHz are supplied to the DD6.1 multiplexer, which is used as an automatic subband selection unit.

The main measurement unit is a single-vibrator assembled on elements DD5.3, DD5.4, the pulse duration of which directly depends on the capacitor connected to it. The principle of measuring capacitance is to count the number of pulses during the operation of a monovibrator. A unit is assembled on elements DD5.1, DD5.2 that prevents bouncing of the contacts of the “Start measurement” button. Well, the last part of the circuit is a four-digit line of binary-decimal counters DD9 - DD12 with output to four seven-segment indicators.

Let's consider the algorithm of the meter's operation. When you press the SB1 button, the DD8 binary counter is reset and switches the range node (DD6.1 multiplexer) to the lowest measurement range - 0.010 - 10.00 µF. In this case, pulses with a frequency of 1 MHz are received at one of the inputs of the electronic key DD1.3. The second input of the same switch receives an enabling signal from the one-shot device, the duration of which is directly proportional to the capacitance of the capacitor being measured.

Thus, pulses with a frequency of 1 MHz begin to arrive at the counting decade DD9...DD12. If a decade overflow occurs, the carry signal from DD12 increases the readings of the counter DD8 by one and allows zero to be written to the trigger DD7 at input D. This zero turns on the driver DD5.1, DD5.2 and it, in turn, resets the counting decade and sets DD7 again to “1” and restarts the monostable. The process is repeated, but the counting decade now receives a frequency of 100 kHz through the switch (the second range is turned on).

If before the completion of the pulse from the one-shot device the counting decade overflows again, then the range changes again. If the one-shot switches off earlier, the counting stops and the indicator can read the value of the capacitance connected for measurement. The final touch is the decimal point control unit, which indicates the current measurement subrange. Its functions are performed by the second part of the DD6 multiplexer, which illuminates the desired point depending on the included subband.

IV6 vacuum luminescent indicators are used as indicators in the circuit, so the power supply of the meter must produce two voltages: 1 V for filament and +12 V for anode power supply of lamps and microcircuits. If the indicators are replaced with LCDs, then you can get by with one +9V source, but the use of LED matrices is impossible due to the low load capacity of the DD9...DD12 microcircuits.

It is better to use a multi-turn resistor as a calibration resistor R8, since the measurement error of the device will depend on the accuracy of the calibration. The remaining resistors can be MLT-0.125. Regarding microcircuits, you can use any of the K1561, K564, K561, K176 series in the device, but you should keep in mind that the 176 series is very reluctant to work with a quartz resonator (DD1).

Setting up the device is quite simple, but it should be done with special care.

• Temporarily disconnect the SB1 button from DD8 (pin 13).
• Apply rectangular pulses with a frequency of approximately 50-100 Hz to the connection point between R3 and R2 (any simple generator on a logic chip will do).
• In place of the capacitor being measured, connect a standard one, the capacitance of which is known and lies in the range of 0.5 - 4 µF (for example, K71-5V 1 µF ± 1%). If possible, it is better to measure the capacitance using a measuring bridge, but you can also rely on the capacitance indicated on the case. Here you need to keep in mind that how accurately you calibrate the device, so it will measure you in the future.
• Using trimming resistor R8, set the indicator readings as accurately as possible in accordance with the capacitance of the reference capacitor. After calibration, it is better to seal the trimming resistor with a drop of varnish or paint.

Based on materials from “Radio Amateur” No. 5, 2001.