With this capacitance meter you can easily measure any capacitance from units of pF to hundreds of microfarads. There are several methods for measuring capacitance. This project uses the integration method.

The main advantage of using this method is that the measurement is based on time measurement, which can be done quite accurately on an MC. This method is very suitable for a homemade capacitance meter, and it can also be easily implemented on a microcontroller.

Working principle of a capacitance meter

Phenomena that occur when the state of a circuit changes are called transient processes. This is one of the fundamental concepts of digital circuits. When the switch in Figure 1 is open, the capacitor is charged through resistor R, and the voltage across it will change as shown in Figure 1b. The relationship determining the voltage on the capacitor has the form:

Values ​​are expressed in SI units, t seconds, R ohms, C farads. The time during which the voltage on the capacitor reaches the value V C1 is approximately expressed by the following formula:

From this formula it follows that time t1 is proportional to the capacitance of the capacitor. Therefore, the capacitance can be calculated from the charging time of the capacitor.

Scheme

To measure the charging time, a comparator and a microcontroller timer and a digital logic chip are sufficient. It is quite reasonable to use the AT90S2313 microcontroller (the modern analogue is ATtiny2313). The output of the comparator is used as a flip-flop T C1. The threshold voltage is set by a resistor divider. Charging time does not depend on supply voltage. The charging time is determined by formula 2, therefore it does not depend on the supply voltage because the ratio in the formula VC 1 /E is determined only by the divisor coefficient. Of course, during measurement the supply voltage must be constant.

Formula 2 expresses the time it takes to charge the capacitor from 0 volts. However, it is difficult to work with voltage close to zero due to the following reasons:

• The voltage does not drop to 0 volts. It takes time for the capacitor to fully discharge. This will lead to increased measurement times.
• Time required between startscharging and starting the timer. This will cause measurement error. For AVR this is not critical because this requires only one clock cycle.
• Leakage current at the analog input. According to the AVR datasheet, current leakage increases when the input voltage is close to zero volts.

To prevent these difficulties, two threshold voltages VC 1 (0.17 Vcc) and VC 2 (0.5 Vcc) were used. Surface printed circuit board must be clean to minimize leakage currents. The required supply voltage for the microcontroller is provided by a DC-DC converter powered by a 1.5VAA battery. Instead of a DC-DC converter, it is advisable to use 9 Vbattery and converter 78 L05, preferablyAlsodon't turn offBOD, otherwise problems may arise with EEPROM.

Calibration

To calibrate the lower range: Using the SW1 button. Next, connect pin #1 and pin #3 on P1, insert a 1nF capacitor and press SW1.

To calibrate the high range: Close pin #4 and #6 of connector P1, insert a 100nF capacitor and press SW1.

The inscription “E4” when turned on means that the calibration value was not found in the EEPROM.

Usage

Automatic ranging

Charging starts through a 3.3M resistor. If the voltage on the capacitor does not reach 0.5 Vcc in less than 130 mS (>57nF), the capacitor is discharged and recharged, but through a 3.3 kOhm resistor. If the voltage on the capacitor does not reach 0.5 Vcc in 1 second (>440µF), the inscription “E2”. When time is measured, the capacity is calculated and displayed. The last segment displays the measuring range (pF, nF, µF).

Clamp

You can use part of a socket as a clamp. When measuring small capacitances (units of picofarads), the use of long wires is undesirable.

Capacitors are used in electrical circuits different types. First of all, they differ in capacity. In order to determine this parameter, special meters are used. These devices can be produced with different contacts. Modern modifications are distinguished by high measurement accuracy. In order to make a simple capacitor capacitance meter with your own hands, you need to familiarize yourself with the main components of the device.

How does the meter work?

The standard modification includes a module with an expander. The data is displayed on the display. Some modifications operate on the basis of a relay transistor. It is capable of operating at different frequencies. However, it is worth noting that this modification is not suitable for many types of capacitors.

Low precision devices

You can make a low-precision ESR meter of capacitor capacitance with your own hands using an adapter module. However, the expander is used first. It is more expedient to select contacts for it with two semiconductors. With an output voltage of 5 V, the current should be no more than 2 A. Filters are used to protect the meter from failures. Tuning should be carried out at a frequency of 50 Hz. Tester in in this case should show a resistance no higher than 50 Ohms. Some people have problems with cathode conductivity. In this case, the module should be replaced.

Description of high precision models

When making a capacitor capacitance meter with your own hands, the accuracy calculation should be made based on the linear expander. The overload indicator of the modification depends on the conductivity of the module. Many experts advise choosing a dipole transistor for the model. First of all, it is able to operate without heat loss. It is also worth noting that the presented elements rarely overheat. A contactor for the meter can be used with low conductivity.

To make a simple, accurate capacitor capacitance meter with your own hands, you should take care of a thyristor. The specified element must operate at a voltage of at least 5 V. With a conductivity of 30 microns, the overload in such devices, as a rule, does not exceed 3 A. Filters are used of different types. They should be installed after the transistor. It is also worth noting that the display can only be connected via wired ports. To charge the meter, 3 W batteries are suitable.

How to make an AVR series model?

You can make a capacitor capacitance meter with your own hands, AVR, only on the basis of a variable transistor. First of all, a contactor is selected for modification. To set up the model, you should immediately measure the output voltage. The negative resistance of the meters should not exceed 45 ohms. With a conductivity of 40 microns, the overload in the devices is 4 A. To ensure maximum measurement accuracy, comparators are used.

Some experts recommend choosing only open filters. They are not afraid of impulse noise even under heavy load. Pole stabilizers in lately are in great demand. Only grid comparators are not suitable for modification. Before turning on the device, a resistance measurement is made. For quality models this parameter is approximately 40 ohms. However, in this case, much depends on the frequency of modification.

Setting up and assembling a model based on PIC16F628A

Making a capacitor capacitance meter with your own hands using the PIC16F628A is quite problematic. First of all, an open transceiver is selected for assembly. The module can be used as an adjustable type. Some experts do not recommend installing high conductivity filters. Before soldering the module, the output voltage is checked.

If the resistance is increased, it is recommended to replace the transistor. In order to overcome impulse noise, comparators are used. You can also use conductor stabilizers. Displays are often of the text type. They should be installed through channel ports. The modification is configured using a tester. If the capacitance parameters of the capacitors are too high, it is worth replacing transistors with low conductivity.

Model for electrolytic capacitors

If necessary, you can make a capacitance meter for electrolytic capacitors with your own hands. Store models of this type are distinguished by low conductivity. Many modifications are made on contactor modules and operate at a voltage of no more than 40 V. Their protection system uses class RK.

It is also worth noting that meters of this type are characterized by a reduced frequency. Their filters are only of the transition type; they are able to effectively cope with impulse noise, as well as harmonic oscillations. If we talk about the disadvantages of modifications, it is important to note that they have a small throughput. They perform poorly in high humidity conditions. Experts also point out incompatibility with wired contactors. The devices cannot be used in alternating current circuits.

Modifications for field capacitors

Devices for field capacitors are characterized by reduced sensitivity. Many models are capable of operating from straight-line contactors. Devices are most often used of the transitional type. In order to make the modification yourself, you need to use an adjustable transistor. Filters are installed in sequential order. To test the meter, small capacitors are first used. In this case, the tester detects a negative resistance. If the deviation is more than 15%, it is necessary to check the performance of the transistor. The output voltage on it should not exceed 15 V.

2V devices

At 2 V, a DIY capacitor capacitance meter is quite simple to make. First of all, experts recommend preparing an open transistor with low conductivity. It is also important to choose a good modulator for it. Comparators are usually used with low sensitivity. The protection system of many models is used in the KR series on mesh-type filters. To overcome impulse oscillations, wave stabilizers are used. It is also worth noting that the assembly of the modification involves the use of a three-pin extender. To set up the model, you should use a contact tester, and the resistance should not be lower than 50 Ohms.

3V modifications

When folding a capacitor capacitance meter with your own hands, you can use an adapter with an expander. It is more advisable to select a linear type transistor. On average, the conductivity of the meter should be 4 microns. It is also important to secure the contactor before installing the filters. Many modifications also include transceivers. However, these elements are not capable of working with field capacitors. Their maximum capacitance parameter is 4 pF. The protection system of the models is RK class.

4 V models

It is allowed to assemble a capacitor capacitance meter with your own hands only using linear transistors. The model will also require a high-quality expander and adapter. According to experts, it is more advisable to use transitional type filters. If we consider market modifications, they can use two expanders. Models operate at a frequency of no more than 45 Hz. At the same time, their sensitivity often changes.

If you assemble a simple meter, then the contactor can be used without a triode. It has low conductivity, but is able to work under heavy load. It is also worth noting that the modification should include several pole filters that will pay attention to harmonic oscillations.

Modifications with a single junction expander

Making a capacitor capacitance meter with your own hands based on a single-junction expander is quite simple. First of all, it is recommended to select a module with low conductivity for modification. The sensitivity parameter should be no more than 4 mV. Some models have a serious conductivity problem. Transistors are usually used of the wave type. When using mesh filters, the thyristor heats up quickly.

To avoid such problems, it is recommended to install two filters on mesh adapters at once. At the end of the work, all that remains is to solder the comparator. To improve the performance of the modification, channel stabilizers are installed. It is also worth noting that there are devices based on variable contactors. They are capable of operating at a frequency of no more than 50 Hz.

Models based on two-junction expanders: assembly and configuration

It is quite simple to assemble a digital capacitor capacitance meter on two-junction expanders with your own hands. However, only adjustable transistors are suitable for normal operation of the modifications. It is also worth noting that during assembly you need to select pulse comparators.

The display for the device is of the line type. In this case, the port can be used for three channels. To solve problems with distortion in the circuit, low sensitivity filters are used. It is also worth noting that modifications must be assembled using diode stabilizers. The model is configured with a negative resistance of 55 Ohms.

DIY capacitor capacitance meter— below is a diagram and description of how, without much effort, you can independently make a device for testing the capacitance of capacitors. Such a device can be very useful when purchasing containers on the radio-electronic market. With its help, low-quality or defective electrical charge storage element can be easily identified. The schematic diagram of this ESR, as most electronics engineers usually call it, is not anything complicated, and even a novice radio amateur can assemble such a device.

Moreover, the capacitor capacitance meter does not require a long time and large financial costs for its assembly; it literally takes two to three hours to manufacture a probe of equivalent series resistance. It is also not necessary to run to a radio store - any radio amateur will probably have unused parts suitable for this design. All you need to replicate this circuit is a multimeter of almost any model, but preferably one that is digital and has a dozen parts. There is no need to make any alterations or upgrades to the digital tester; all that needs to be done with it is to solder the pins of the parts to the required pads on its board.

Schematic diagram of the ESR device:

List of elements required to assemble the meter:

One of the main components of the device is a transformer, which should have a turns ratio of 11:1. Ferrite ring core M2000NM1-36 K10x6x3, which must first be wrapped with insulating material. Then wind the primary winding on it, arranging the turns according to the principle - turn to turn, while filling the entire circle. The secondary winding must also be made with a uniform distribution around the entire perimeter. The approximate number of turns in the primary winding for the K10x6x3 ring will be 60-90 turns, and the secondary should be eleven times smaller.

You can use almost any silicon diode D1 with a reverse voltage of at least 40v; if you don’t really need super precision in measurements, then the KA220 is quite suitable. To more accurately determine the capacitance, you will have to install a diode with a small voltage drop in the direct connection version - Schottky. The protective suppressor diode D2 must be designed for reverse voltage from 28v to 38v. Low-power silicon pnp transistor: for example KT361 or its analogue.

Measure the ESR value in the voltage range of 20v. When connecting the connector of an external meter, the ESR attachment to the multimeter immediately switches to the capacitance testing operating mode. In this case, a reading of about 35v will be visually displayed on the device in the test range of 200v and 1000v (this depends on the use of a suppressor diode). In the case of testing capacitance at 20 volts, the reading will be displayed as “out of measurement limits”. When the connector of the external meter is disconnected, the EPS attachment instantly switches to operating mode as an ordinary multimeter.

Conclusion

The principle of operation of the device is that to start operating the device, you need to connect the adapter to the network, and the ESR meter turns on; when the ESR is turned off, the multimeter automatically switches to the mode of performing standard functions. To calibrate the device, you need to select a constant resistor so that it matches the scale. For clarity, the picture is below:

When the probes are shorted, 0.00-0.01 will be displayed on the multimeter scale; this reading means the instrument’s error in the measurement range up to 1 ohm.

This article provides an elementary circuit of a capacitance meter on a logic chip. Such a classic and elementary circuit solution can be reproduced quite quickly and easily. Therefore, this article will be useful to a novice radio amateur who is planning to assemble a basic capacitor capacitance meter.

Operation of the capacitance meter circuit:

List of capacitance meter elements:

R1- R4 – 47 KOhm

R5 – 1.1 KOhm

C3 – 1500 pF

C4 – 12000 pF

C5 –0.1 µF

C meas. – capacitor whose capacitance you want to measure

SA1 – roller switch

DA1 – K155LA3 or SN7400

VD1-VD2– KD509 or analogue 1N903A

PA1 – Pointer indicator head (total deflection current 1 mA, frame resistance 240 Ohm)

XS1- XS2 – crocodile connectors

This version of the capacitance meter has four ranges, which can be selected using switch SA1. For example, in position “1” you can measure capacitors with a capacity of 50 pF, in position “2” - up to 500 pF, in position “3” - up to 5000 pF, in position “4” - up to 0.05 µF.

The elements of the DA1 microcircuit provide sufficient current to charge the measured capacitor (C measured). It is especially important for measurement accuracy to adequately select diodes VD1-VD2; they must have the same (most similar) characteristics.

Setting up the capacitance meter circuit:

Setting up such a circuit is quite simple; you need to connect C change. with known characteristics (with known capacity). Select the required measurement range with the switch SA1 and rotate the knob of the construction resistor until you achieve the desired reading on the indicator head PA1 (I recommend calibrating it in accordance with your readings, this can be done by disassembling the indicator head and gluing a new scale with new inscriptions)

Almost two years ago I bought a digital capacity meter and, one might say, took the first thing I came across. I was so tired of the inability of the Mastech MY62 multimeter to measure the capacitance of capacitors greater than 20 microfarads, and it did not correctly measure less than 100 picofarads. I liked two things about the SM-7115A:

1. Measures the entire required range
2. Compact and convenient

Paid 750 rubles. I sincerely believed that it was not worth the money, and the price was “inflated” due to the complete lack of competitive products. The country of origin is, of course, China. He was afraid that he would “fib”; moreover, he was sure of it - but in vain.

The capacitance meter and the wires to it were packed in polyethylene, each in its own shell and placed in a box made of thick cardboard, the free space was filled with foam plastic. The box also contained instructions in English. Overall dimensions of the device are 135 x 72 x 36 mm, weight 180 grams. The body color is black, the front panel has a lilac tint. It has a liquid crystal indicator, nine measurement ranges, two power-off positions, a zero adjustment regulator, 15 centimeter, different colored (red - black) wires, with which the measured capacitor is connected to the device, ending with alligator clips, and the sockets on the device body , for their connection, are marked with a color designation of the corresponding polarity; it is additionally possible to measure without them (which increases accuracy), for which there are two elongated sockets, which are signed with the symbol of the capacitor being measured. A 9-volt battery is used and there is a function for automatically indicating its discharge. Three-digit liquid crystal indicator +1 decimal place, the measurement range declared by the manufacturer is from 0.1 pF to 20000 μF, with the ability to adjust the measurement range from 0 to 200 pF, to set zero, within +/- 20 pF, time of one measurement 2-3 seconds.

Table of permissible errors in measurements, individually by range. Provided by the manufacturer.

There is an integrated stand on the back half of the case. It makes it possible to place the meter more compactly at the workplace and improves the visibility of the liquid crystal display.

The battery compartment is completely autonomous; to change the battery, just move its cover to the side. Convenience is inconspicuous when it exists.

To remove the back cover of the case, just unscrew one screw. The heaviest component on the PCB is the 500mA fuse.

The operation of the measuring device is based on the double integration method. It is assembled on logical counters HEF4518BT - 2 pcs., key HEF4066BT, decimal counter with decoder HCF4017 and SMD transistors: J6 - 4 pcs., M6 - 2 pcs.

By unscrewing six more screws you can see the other side of the printed circuit board. The variable resistor used to set it to “0” is positioned so that it can be easily replaced if necessary. On the left are the contacts for connecting the capacitor being measured, those above are for direct connection (without wires).

The device is not immediately set to the zero reference point, but the adjusted reading remains. It's much easier to do this with the wires disconnected.

To clearly demonstrate the difference in measurement accuracy when different ways measurements (with and without wires) I took small capacitors with factory markings - 8.2 pF

Video review of the device

Without wires With wires
№1 8 pF 7.3 pF
№2 7.6 pF 8.3 pF
No. 3 8.1 pF 9.3 pF

Everything is clear; measurements will definitely be more accurate without wires, although the discrepancy is practically within 1 pF. I also repeatedly measured the capacitors on the boards - the measurement readings of serviceable ones are quite adequate according to the value indicated on them. Without being too picky, we can say that the measurement quality factor of the device is quite high.

Disadvantages of the device

• zeroing is not done immediately,
• the contact blades, for measuring without wires, have no elasticity, after being unclenched in starting position don't return
• The meter is not equipped with a calibration container.

Conclusions

In general, I am satisfied with the device. It measures well, is compact (easily fits in a pocket), so on the radio market I take not what they give, but what I need. I plan to modify it when I have time: replace the potentiometer and direct measurement contacts. Its diagram, or something similar, can be found in the section. He told it “as it is,” and you can decide for yourself whether it’s worth adding such a device to your home laboratory. Author - Babay.