Universal measuring complex. Universal measuring complex Schematic diagram of a capacitance and induction meter
As is well known, not a single amateur radio laboratory can do without means of measuring and monitoring the processes occurring in an electronic device. The modern market offers us entire lines of measuring instruments, from the simplest to the most professional, but not everyone, even the most experienced DIYer, will allow their laboratory to have a full range of available equipment. All this is a consequence of high prices for devices, due to the realities of the modern market. But radio amateurs, as always, find a way out of the situation - they independently design and manufacture measuring equipment for their needs. I invite you to familiarize yourself with the experience of repeating one of these devices, designed by Andrei Vladimirovich Ostapchuk (Andrew).
The AVO-2006 universal measuring complex contains a minimum number of non-scarce and inexpensive parts, and taking into account the functionality of the device, I would venture to call it the simplest that I have ever encountered in my practice! So, what functions does the device have?
Availability of resistance measurement function in the range from 0 to 200,000,000 ohms;
Availability of a function for measuring the capacitance of capacitors in the range from 0.00001 to 2000 μF;
The presence of a single-beam oscilloscope function that allows you to visualize the signal shape, measure its amplitude value and voltage;
The presence of a frequency signal generator function in the range from 0 to 100,000 Hz with the ability to step-by-step change the frequency in steps of 0-100 Hz and display the frequency and duration values on the display;
The presence of a frequency measurement function in the range from 0.1 to 15,000,000 Hz with the ability to change the measurement time and display the frequency and duration values on the display.
If you are impressed by the list of functions supported by the device, I suggest moving on to the recommendations for its manufacture. First of all, a few notes on the components of the device. The most expensive and important part is an LCD indicator with 2 lines of 16 characters each, with a built-in HD44780 controller or its equivalent. The most common are indicators from Winstar and MELT (although my personal preference is Winstar with Russian and Latin fonts). Capacitor C5 should be selected as thermally stable as possible, a film capacitor - the accuracy of measurements of resistance parameters will depend on the invariance of its parameters.
Another important part is the protective zener diode VD1. I’ll make a reservation right away - the use of domestic KS156 zener diodes is impossible, since they have low reverse resistance, and the performance of the device depends on it - the higher the reverse resistance of the zener diode, the better. Imported zener diodes marked on the case 5V6 or 5V1 are ideal for these purposes. The Atmega8A-PU microcontrollers (analogue of the old Atmega8-16PI and Atmega8-16PU) are ideal for the manufacture of the device, but since today there are many Chinese analogues of these controllers, with old markings, failures in the operation of the device are not excluded - here we are Unfortunately, we cannot help.
Before starting to manufacture the device, I advise you to take a closer look at the LCD indicator. It is better to download the datasheet from the manufacturer’s website (Winstar-www.winstar.com.tw or MELT-www.melt.com.ru). Next, strictly following the datasheet, we connect the screen to the device’s power supply (this can be a simple transformer power supply with an LM317 stabilizer (K142EN5A)
or a 6-volt gel (or any other small-sized and lightweight) battery with the same stabilizer (if someone needs to make a meter for field work). We apply +5 volt voltage to pin 2 of the indicator (see the datasheet - the power pins may change!), and apply the minus voltage to pins 1 and 5. We connect pin 3 of the indicator through a 10 kOhm trimming resistor to the minus power supply. By rotating the resistor, we achieve a clear and contrasting display of the entire top line of the indicator. We remove the resistor, measure its resistance and select the same constant - so we have selected resistor R4 for our circuit. We carry out a similar procedure when connecting the display backlight - having achieved optimal brightness, we select a constant resistor - this will be resistor R5 of our circuit. Another important procedure is flashing the microcontroller firmware. Download the HEX file from the author’s website and stitch it into our controller using , not forgetting about the controller’s fuse bits.
You can assemble the device on a breadboard, its wiring is so simple. After the first launch of the device, we begin to calibrate it. To do this, in the resistance measurement mode, when calibrating to zero, we close the measuring probes (crocodiles) with each other, press and hold button 1 and simultaneously press button 2 (save it into memory - OK appears on the screen).
Next, we perform calibration at a nominal value of 1000 Ohm - we attach a precision resistor, press and hold button 2 and simultaneously press button 1 (save it into memory). The device modes are switched in a ring using button 3. To calibrate the device in the capacitance measurement mode, perform the following steps. When calibrating to 0, open the meter probes and press and hold button 1 and write to memory using button 2. When calibrating to 1000pF, attach a precision capacitor, press and hold button 2 and write to memory with button 1. That’s it, the device is ready for use . In other modes, no calibrations are performed.
You can check the operation of the oscilloscope and frequency counter by connecting the device to some kind of working circuit, the measurement results from which were taken in advance using another oscilloscope and frequency counter. You can check the operation of the frequency generator by simply connecting a regular speaker to the output of the device and smoothly changing the frequency using the adjustment keys (1 and 2). The same keys are used to change the sweep time in oscilloscope mode. Changing the frequency measurement time (in frequency meter mode) is carried out by button 1, which allows you to measure frequency with an accuracy of 0.1 Hz.
One small note - make measurements, calibrations and adjustments only with ready-made shielded probes (and not with pieces of mounting wire) - practice shows that different types of cable can introduce significant distortions into the measurement results.
Precision K71-7 are excellent as calibration capacitors, and S2-33N are excellent as calibration resistors.
All parts with a deviation from the nominal value of no more than 1 percent. If, as a result of initial control measurements, it turns out that the linearity of capacitance measurements is too low, we change the resistance of resistor R3 in the range of 50-220 kOhm (the higher the value of this resistor, the higher the accuracy of measurements of small capacitances will be, but accordingly the time for measuring large capacitances will increase significantly); if the linearity of resistance measurement is low, then you will have to select the capacitance of capacitor C5 (of course, you can only change it to one that is equally thermally stable).
Here is a brief summary of all the recommendations for assembling and setting up the device. I gave my device for testing to a friend who works in the instrumentation shop of a local enterprise, and for comparison I also gave him a Chinese measuring device XC4070L (LCR meter). So - according to the results of control measurements made on the enterprise's precision equipment, the AVO-2006 device surpassed the Chinese meter in the accuracy of measuring capacitances and resistances! So draw your own conclusions and stay tuned for further publications in this area.
I am sure that this project is not new, but it is my own development and I want this project to be well-known and useful.
Scheme LC meter on ATmega8 quite simple. The oscillator is classic and is based on an LM311 operational amplifier. The main goal that I pursued when creating this LC meter was to make it inexpensive and affordable for every radio amateur to assemble.
Schematic diagram of a capacitance and induction meter
LC Meter Features:
- Capacitance measurement of capacitors: 1pF - 0.3 µF.
- Coil inductance measurement: 1uH-0.5mH.
- Information output on LCD indicator 1×6 or 2×16 characters depending on the selected software
For this device, I have developed software that allows you to use the indicator that a radio amateur has at his disposal, either a 1x16 character LCD display or 2x 16 characters.
Tests from both displays gave excellent results. When using a 2x16 character display, the top line displays the measurement mode (Cap – capacitance, Ind –) and the generator frequency, and the bottom line displays the measurement result. The 1x16 character display shows the measurement result on the left, and the generator operating frequency on the right.
However, in order to fit the measured value and frequency onto one line of characters, I reduced the display resolution. This does not affect the accuracy of the measurement in any way, only purely visually.
As with other well-known options that are based on the same universal circuit, I added a calibration button to the LC meter. Calibration is carried out using a 1000pF reference capacitor with a deviation of 1%.
When you press the calibration button, the following is displayed:
The measurements taken with this meter are surprisingly accurate, and the accuracy largely depends on the accuracy of the standard capacitor that is inserted into the circuit when you press the calibration button. The device calibration method simply involves measuring the capacitance of a reference capacitor and automatically recording its value into the microcontroller’s memory.
If you don't know the exact value, you can calibrate the meter by changing the measurement values step by step until you get the most accurate capacitor value. For such calibration there are two buttons, please note that in the diagram they are designated as “UP” and “DOWN”. By pressing them you can adjust the capacitance of the calibration capacitor. This value is then automatically written to memory.
Before each capacitance measurement, the previous readings must be reset. Reset to zero occurs when “CAL” is pressed.
To reset in inductive mode, you must first short-circuit the input pins and then press “CAL”.
The entire installation is designed taking into account the free availability of radio components and in order to achieve a compact device. The size of the board does not exceed the size of the LCD display. I used both discrete and surface mount components. Relay with operating voltage 5V. Quartz resonator - 8MHz.
Stepan Mironov.
ESR+LCF v3 meter.
It has long been no secret that half of the failures in modern household appliances are associated with electrolytic capacitors.
Swollen capacitors are immediately visible, but there are also those that look quite normal. All faulty capacitors have a loss of capacity and an increased ESR value, or only an increased ESR value (the capacity is normal or higher than normal).
Calculating them is not so easy; you have to unsolder them, if several capacitors are connected in parallel, or if any shunt elements are connected in parallel to the capacitor being measured, check them and solder them back into working order. Many capacitors are glued to the board, located in hard-to-reach places and dismantling/installing them takes a lot of time. Even when heated, a faulty capacitor can temporarily restore its functionality.
Therefore, radio mechanics, and not only them, dream of having a device for checking the serviceability of electrolytic capacitors, in-circuit, without desoldering them.
I want to disappoint you, it’s 100% impossible. It is not possible to correctly measure capacitance and ESR, but it is possible to check the serviceability of an electrolytic capacitor without soldering, in many cases using an increased ESR value.
Faulty capacitors with increased ESR and normal capacity are common, but those with normal ESR and loss of capacity are not.
A 20% decrease in capacitance from the nominal value is not considered a defect, this is normal even for new capacitors, so for the initial defectiveness of an electrolytic capacitor, it is enough to measure the ESR. In-circuit capacitance readings, for information only and depending on the shunt elements in the circuit, may be significantly overestimated or may not be measured.
An indicative table of acceptable ESR values is given below:
Several versions of the ESR meter have been developed.
The ESR+LCF v3 meter (third version) was developed taking into account maximum capabilities for in-circuit measurements. In addition to the main ESR measurement (display Rx>x.xxx), there is an additional function for in-circuit ESR calculation, called "aESR" by the analyzer (display a x.xx).
The analyzer detects nonlinear areas when charging the measured capacitor (a working capacitor is charged linearly). Next, the estimated deviation is calculated mathematically and added to the ESR value.
When measuring a working capacitor, “aESR” and “ESR” are close in value. The display additionally shows the value “aESR”.
This function does not have a prototype, so at the time of preparing the main documentation, there was very little experience in using it.
At the moment, there are many positive reviews from different people with recommendations for its use.
This mode does not give a hundred percent result, but with knowledge of circuit design and accumulated experience, the effectiveness of this mode is great.
The result of an in-circuit measurement depends on the shunting influence of the circuit elements.
Semiconductor elements (transistors, diodes) do not affect the measurement result.
The greatest influence is exerted by low-resistance resistors, inductors, as well as other capacitors connected to the circuits of the measured capacitor.
In places where the shunting effect on the capacitor being tested is not large, the faulty capacitor can be measured well in the normal "ESR" mode, and in places where the shunting effect is large, the faulty capacitor (without desoldering) can only be calculated using the "analyzer - aESR".
It should be remembered that when making in-circuit measurements of healthy electrolytic capacitors, the "aESR" readings in most cases are slightly higher than the "ESR" readings. This is normal, since multiple connections to the capacitor being measured introduce error.
The most difficult places to measure are circuits with simultaneous shunting of many elements of different types.
In the diagram above, the faulty capacitor C2+1ohm is shunted by C1+L1+C3+R2.
When measuring such a capacitor, the ESR value is normal, but the analyzer shows “0.18” - this is exceeding the norm.
Unfortunately, it is not always possible to determine the serviceability of an electrolytic capacitor within the circuit.
For example: in motherboards it will not work to power the processor, the shunting there is too large. A radio mechanic, as a rule, repairs equipment of the same type, and over time he gains experience, and he already knows exactly where and how electrolytic capacitors are diagnosed.
So, what can my meter do?
ESR+LCF v3 meter - measures
Additional functions:
In ESR mode, you can measure constant resistances of 0.001 - 100 Ohm; measuring the resistance of circuits with inductance or capacitance is impossible (since the measurement is performed in pulse mode and the measured resistance is shunted). To correctly measure such resistances, you must press the “+” button (in this case, the measurement is performed at a constant current of 10 mA). In this mode, the range of measured resistances is 0.001 - 20 Ohm.
- In ESR mode, pressing the “L/C_F/P” button turns on the in-circuit analyzer function (see below for a detailed description).
- In frequency meter mode, when the “Lx/Cx_Px” button is pressed, the “pulse counter” function is activated (continuous counting of pulses arriving at the “Fx” input). The counter is reset using the “+” button.
- Low battery indication.
- Automatic shutdown - about 4 minutes (in ESR mode - 2 minutes). After the idle time has expired, the inscription “StBy” lights up and within 10 seconds, you can press any button and work will continue in the same mode.
In modern technology, electrolytic capacitors are often bypassed with inductance less than 1 μH and ceramic capacitors. In normal mode here, the meter is not able to detect a faulty electrolytic capacitor without desoldering. For these purposes, an in-circuit analyzer function has been added.
The analyzer detects nonlinear areas when charging the measured capacitor (a working capacitor is charged linearly). Next, the expected deviation is calculated mathematically and added to the value ESR(Rx) = aESR(a). The display also shows the aESR (a) value. This function is most effective when measuring capacitances above 300 µF. To enable this function, you must press the “L/C_F/P” button.
Schematic diagram.
“The heart of the meter is the PIC16F886-I/SS microcontroller. This meter can also operate PIC16F876, PIC16F877 microcontrollers without changing the firmware.
Construction and details.
LCD indicator based on the HD44780 controller, 2 lines of 16 characters.
Controller - PIC16F886-I/SS.
Transistors BC807 - any P-N-P, similar in parameters.
Op-amp TL082 - any of this series (TL082CP, AC, etc.). It is possible to use the MC34072 op-amp. The use of other op-amps (with different speeds) is not recommended.
Field effect transistor P45N02 - 06N03, P3055LD, etc., fits almost any computer motherboard.
Choke L101 - 100 µH + -5%. You can make it yourself or use a ready-made one. The diameter of the winding wire must be at least 0.2mm.
S101 - 430-650pF with low TKE, K31-11-2-G - can be found in the KOS of domestic 4-5 generation TVs (KVP circuit).
C102, C104 4-10uF SMD - can be found in any old Pentium-3 computer motherboard near the processor, as well as in a Pentium-2 boxed processor.
BF998 - can be found in VCRs, TVs and VCRs GRUNDIK.
SW1 (size 7*7mm) - pay attention to the pinout, there are two types. The PCB layout corresponds to Fig. 2.
The printed circuit board is made of single-sided fiberglass.
At the same time, the printed circuit board serves as the base for the housing. 21mm wide fiberglass strips are soldered around the perimeter of the board.
The covers are made of black plastic.
There are control buttons on top, and in front there are three TULIP type sockets for a removable probe. For the “R/ESR” mode - a higher quality socket.
Probe design:
A metal tulip-type plug was used as a probe. A needle is soldered to the central pin.
From the available material, a brass rod with a diameter of 3 mm can be used to make a needle. After some time, the needle oxidizes and to restore reliable contact, it is enough to wipe the tip with fine sandpaper.
Below in the archive there are all the necessary files and materials for assembling and configuring this meter.
Good luck to everyone and all the best!
miron63.
Archive ESR+LCF v3 meter.
