Oscilloscope from a computer monitor at home. How to make a digital oscilloscope from a computer with your own hands

An oscilloscope is one of the key instruments in any radio engineering laboratory for industrial use, as well as in an ordinary radio workshop. Using such a device, you can determine faults in electronic circuits, as well as debug their operation when designing new devices. However, the price of this kind of devices is very high, and not every radio amateur can afford to purchase such a thing. This article is devoted to the question of how to make it. There are many ways to make such a device, but the basis is the same everywhere: a PC sound card serves as the board that will receive pulses, and a special adapter is attached to it. It serves to match the levels of the measured signals and the input of the computer audio card.

Oscilloscope on a computer: software

One of the main elements of the mentioned device is a program that visualizes the measured pulses on the monitor. There is a huge selection of such software, but not all utilities work stably. The Osci oscilloscope program from the AudioTester kit is especially popular among radio amateurs. It has an interface that looks similar to a standard analog device; there is a grid on the screen that allows you to measure the duration and amplitude of the signal. It is easy to use and has a number of additional functions that programs of this type do not have. But every radio amateur will be able to choose the software that he likes best for work.

Technical data

So, in order to make an oscilloscope from a computer, you need to assemble a special attenuator (voltage divider) that can cover the widest possible range of the measured voltage. The second function of such an adapter is to protect the input port of the sound card from damage that can be caused by high voltage levels. For most audio cards, the input voltage is limited to 1-2 volts. An oscilloscope from a computer is limited by the capabilities of the sound card. For budget cards it ranges from 0.1Hz to 20kHz (sinusoidal signal). The lower voltage limit that can be measured is limited by the level of background and noise and is 1 mV, and the upper limit is limited by the adapter parameters and can be several hundred volts.

Voltage divider device

An oscilloscope from a computer has a very simple electrical circuit. It contains only two zener diodes and three depend on the virtual oscilloscope scale used. This divider is designed for three different scales, with ratios of 1:1, 1:20 and 1:100. Accordingly, the device will have three inputs, each of which is connected to a resistor. The nominal resistance of the direct input resistor is 1 MΩ. The common wire is connected through the reverse connection of two zener diodes. They are designed to protect the sound card from overvoltage when the switch is in the "direct input" position. Capacitors can be connected in parallel to the resistors; they will equalize the amplitude-frequency component of the device.

Conclusion

This computer-oscilloscope is not elegant, but a simple circuit design will allow you to achieve a wide range of measured voltages. The mentioned device will help in repairing audio equipment or can be used as a training measuring device.

Today, often instead of making, for example, an oscilloscope from a computer, most people prefer to simply purchase a USB oscilloscope. But after shopping, you can see that the price of budget oscilloscopes starts at $200. And serious equipment costs many times more. It is for those people who are not satisfied with this price that the easiest way is to make an oscilloscope from a laptop or computer with your own hands.

What to use

The most optimal today is Osci program, it has an interface similar to a classic oscilloscope: on the monitor there is a standard grid with which you can measure the amplitude or duration yourself.

One of the disadvantages of this program is that it works a little unstable. During operation, the utility may sometimes freeze, and in order to reset it later, you need to use a specialized TaskManager. But all this is compensated by the fact that the program has a familiar interface and is quite easy to use, and also has a large number of functions that make it possible to make a fully functioning oscilloscope from a computer or laptop.

On a note

It must be said that the package of these programs includes special low frequency generator, but its use is undesirable; it tries to completely control the operation of the sound card driver itself, which causes the sound to turn off. If you decide to try it, make sure you have a restore point or make a backup of your OS. The best way to make an oscilloscope from a computer with your own hands is to download a working generator.

"Vanguard"

This is a domestic program, it does not have the usual and standard measuring grid, and has a very large screen for taking screenshots, but at the same time allows you to use the installed frequency meter and voltmeter amplitude values. This partially compensates for the disadvantages mentioned above.

Having made this oscilloscope from a computer, you will encounter the following: at low levels of indicators, a voltmeter and frequency meter can significantly distort the data, but for beginner radio amateurs, this utility will be quite sufficient. Another useful function is that you can do completely independent calibration of the two existing scales of the installed voltmeter.

How to use it

Due to the fact that the input circuits of the sound card have a special isolation capacitor, the computer in the role of an oscilloscope can work only with a closed entrance. Thus, only the variable component of the indicators will be visible on the monitor, but with some skill, using these programs you can measure the indicator with a constant component. This is very important in the case when, for example, the counting time of a multimeter does not make it possible to record a certain value of the voltage amplitude on a capacitor charged using a large resistor.

The lower voltage value is limited by background and noise levels and is approximately 1 mV. The upper limit is limited only by the indicators of the divider and reaches more than a hundred volts. The frequency range is limited by the sound card itself and for older computers is about 20 kHz.

Naturally, in this case a rather primitive device is considered. But when you do not have the opportunity, for example, to use a USB oscilloscope, then in this case its use is quite acceptable. This device will help you in repairing various audio equipment, or can be used for educational purposes. In addition, the oscilloscope program will allow you to save the plot to illustrate the material or for posting on the network.

Electrical diagram

If you need an attachment to your computer, then making an oscilloscope will be much more difficult. Today on the Internet you can find quite a large number of different circuits for these devices, and to make, for example, a two-channel oscilloscope, you will only need to duplicate them. The second channel is often relevant when it is necessary to compare two signals or an oscilloscope is used to connect external synchronization.

As a rule, the circuits are very simple, but this way, you will independently provide a very large range of available measurements using a minimum of radio components. Moreover, the attenuator, which is manufactured according to the classical scheme, would require you to have highly specialized high-ohm resistors, and its input resistance changed all the time when switching the range. Therefore, you would experience some limitations when using conventional oscilloscope leads, which are rated for input impedances of no more than 1 mOhm.

How to choose voltage divider resistors

Due to the fact that radio amateurs often have difficulty selecting precision resistors, it often happens that they have to choose wide-profile devices that need fit as accurately as possible, otherwise you won’t be able to make an oscilloscope from a computer with your own hands.

Voltage divider trimmer resistors

In this case, each arm of the divider has two resistors, one is constant, the second is tuning. The disadvantage of this option is its bulkiness, but the accuracy is limited only by what available characteristics the measuring apparatus has.

How to choose regular resistors

Another option to make an oscilloscope from a computer is to select pairs of resistors. Accuracy in this case is ensured due to the fact that pairs of two sets with a fairly decent spread are used. It is important to initially carry out careful measurements of all devices, and then select pairs whose total resistance will be most suitable for your circuit.

Today, adjusting resistors by removing part of the film is often used even in modern industry, that is, an oscilloscope is often made from a computer.

But it must be said that if you want to customize high-resistance resistors, then the resistive film should not be cut all the way through. Since in these devices it is located on a cylindrical surface in the form of a spiral, therefore the undercut must be made extremely carefully so that prevent the chain from breaking. Then:

After, when the resistor is completely adjusted, place of cut covered with a layer of special protective varnish.

Today this method is the fastest and simplest, but at the same time it gives good results, which made it optimal for home use.

Things to consider

There are a number of rules that must be followed in any case if you decide to carry out this work:

• The computer used for the oscilloscope must be grounded.
• Do not connect the ground to the outlet. It is connected through a special linear input connector housing to the system unit housing. In this case, no matter whether you hit phase or zero, you will not have a short circuit.

In other words, only a wire that can be connected to a socket is connects to resistor, and is located in an adapter circuit with a nominal value of one megohm. If you try to connect a wire that is in contact with the housing into the network, then in almost all cases this will certainly lead to the most disastrous consequences.

Dedicated to beginning radio amateurs!

How to assemble the simplest adapter for a software virtual oscilloscope, suitable for use in repairing and configuring audio equipment. http://oldoctober.com/

The article also talks about how you can measure input and output impedance and how to calculate an attenuator for a virtual oscilloscope.

Related topics.

How to make a probe cable for a low-frequency virtual oscilloscope?

How to connect Notepad with the Windows Calculator to make calculations easier?

How to solder a plug to a shielded cable.

About virtual oscilloscopes.

I once had a fix idea: sell an analog oscilloscope and buy a digital USB oscilloscope to replace it. But, having wandered around the market, I discovered that the most budget oscilloscopes “start” at $250, and the reviews about them are not very good. More serious devices cost several times more.

So, I decided to limit myself to an analog oscilloscope, and to build some diagram for the site, use a virtual oscilloscope.

I downloaded several software oscilloscopes from the network and tried to measure something, but nothing good came of it, since either it was not possible to calibrate the device, or the interface was not suitable for screenshots.

I had already abandoned this matter, but when I was looking for a program to measure the frequency response, I came across the “AudioTester” software package. I didn’t like the analyzer from this kit, but the Osci oscilloscope (hereinafter I will call it “AudioTester”) turned out to be just right.

This device has an interface similar to a conventional analog oscilloscope, and the screen has a standard grid that allows you to measure amplitude and duration. http://oldoctober.com/

The disadvantages include some instability of work. The program sometimes freezes and in order to reset it you have to resort to the help of Task Manager. But, all this is compensated by the familiar interface, ease of use and some very useful functions that I have not seen in any other program of this type.

Attention! The AudioTester software package includes a low frequency generator. I don't recommend using it because it tries to control the audio card driver itself, which can result in permanent audio muting. If you decide to use it, take care of a restore point or an OS backup. But, it’s better to download a normal generator from “Additional materials”.

Another interesting program for the Avangard virtual oscilloscope was written by our compatriot O.L. Zapisnykh.

This program does not have the usual measuring grid, and the screen is too large for taking screenshots, but it does have a built-in amplitude voltmeter and frequency meter, which partially compensates for the above disadvantage.

Partly because at low signal levels both the voltmeter and the frequency meter begin to lie a lot.

However, for a novice radio amateur who is not used to perceiving diagrams in Volts and milliseconds per division, this oscilloscope may be quite suitable. Another useful property of the Avangard oscilloscope is the ability to independently calibrate the two available scales of the built-in voltmeter.

So, I will talk about how to build a measuring oscilloscope based on the AudioTester and Avangard programs. Of course, in addition to these programs, you will also need any built-in or separate, most budget audio card.

Actually, all the work comes down to making a voltage divider (attenuator) that would cover a wide range of measured voltages. Another function of the proposed adapter is to protect the audio card input from damage when high voltage comes into contact with the input.

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Technical data and scope.

Since there is an isolation capacitor in the input circuits of the audio card, the oscilloscope can only be used with a “closed input”. That is, only the variable component of the signal can be observed on its screen. However, with some skill, using the AudioTester oscilloscope you can also measure the level of the DC component. This can be useful, for example, when the multimeter reading time does not allow you to record the amplitude value of the voltage on a capacitor charging through a large resistor.

The lower limit of the measured voltage is limited by the noise level and background level and is approximately 1 mV. The upper limit is limited only by the parameters of the divider and can reach hundreds of volts.

The frequency range is limited by the capabilities of the audio card and for budget audio cards is: 0.1Hz... 20kHz (for a sine wave signal).

Of course, we are talking about a rather primitive device, but in the absence of a more advanced device, this one may well do.

The device can help in repairing audio equipment or be used for educational purposes, especially if it is supplemented with a virtual low-frequency generator. In addition, using a virtual oscilloscope it is easy to save a diagram to illustrate any material, or for posting on the Internet.

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Electrical diagram of the oscilloscope hardware.

The drawing shows the hardware part of the oscilloscope - “Adapter”.

To build a two-channel oscilloscope, you will have to duplicate this circuit. The second channel can be useful for comparing two signals or for connecting external synchronization. The latter is provided in AudioTester.

Resistors R1, R2, R3 and Rin. – voltage divider (attenuator).

The values ​​of resistors R2 and R3 depend on the virtual oscilloscope used, or more precisely on the scales it uses. But, since the “AudioTester” has a division price that is a multiple of 1, 2 and 5, and the “Avangard” has a built-in voltmeter with only two scales interconnected by a ratio of 1:20, then using an adapter assembled according to the above the circuit should not cause inconvenience in both cases.

The input impedance of the attenuator is about 1 megohm. In a good way, this value should be constant, but the design of the divider would be seriously complicated.

Capacitors C1, C2 and C3 equalize the amplitude-frequency response of the adapter.

Zener diodes VD1 and VD2, together with resistors R1, protect the linear input of the audio card from damage in the event of accidental high voltage entering the adapter input when the switch is in the 1:1 position.

I agree that the presented scheme is not elegant. However, this circuit solution makes it possible in the simplest way to achieve a wide range of measured voltages using only a few radio components. An attenuator built according to the classical scheme would require the use of high-megaohm resistors, and its input impedance would change too significantly when switching ranges, which would limit the use of standard oscilloscope cables designed for an input impedance of 1 mOhm.

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Protection from the "fool".

To protect the linear input of the audio card from accidental high voltage, zener diodes VD1 and VD2 are installed parallel to the input.

Resistor R1 limits the current of the zener diodes to 1 mA, at a voltage of 1000 Volts at the 1:1 input.

If you really intend to use an oscilloscope to measure voltages up to 1000 Volts, then as resistor R1 you can install MLT-2 (two-watt) or two MLT-1 (one-watt) resistors in series, since the resistors differ not only in power, but also according to the maximum permissible voltage.

Capacitor C1 must also have a maximum allowable voltage of 1000 Volts.

A little clarification of the above. Sometimes you want to look at a variable component of relatively small amplitude, which nevertheless has a large constant component. In such cases, you need to keep in mind that on the screen of an oscilloscope with a closed input, you can only see the alternating voltage component.

The picture shows that with a constant component of 1000 Volts and a swing of the variable component of 500 Volts, the maximum voltage applied to the input will be 1500 Volts. Although, on the oscilloscope screen we will only see a sine wave with an amplitude of 500 Volts.

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How to measure the output impedance of a line output?

You can skip this paragraph. It is designed for lovers of small details.

The output resistance (output impedance) of a line output designed to connect phones (headphones) is too low to have a significant impact on the accuracy of the measurements we will perform in the next paragraph.

So why measure output impedance?

Since we will use a virtual low-frequency signal generator to calibrate the oscilloscope, its output impedance will be equal to the output impedance of the Line Out of the sound card.

By making sure that the output impedance is low, we can prevent gross errors when measuring the input impedance. Although, even under the worst circumstances, this error is unlikely to exceed 3... 5%. Frankly, this is even less than the possible measurement error. But it is known that errors have a habit of “running up”.

When using a generator to repair and tune audio equipment, it is also advisable to know its internal resistance. This can be useful, for example, when measuring ESR (Equivalent Series Resistance) or simply the reactance of capacitors.

Thanks to this measurement, I was able to identify the lowest impedance output in my audio card.

If the audio card has only one output jack, then everything is clear. It is both a line output and an output for phones (headphones). Its impedance is usually small and does not need to be measured. These are the audio outputs used in laptops.

When there are as many as six sockets and there are a couple more on the front panel of the system unit, and each socket can be assigned a specific function, then the output impedance of the sockets can differ significantly.

Typically, the lowest impedance corresponds to the light green jack, which by default is the line output.

An example of measuring the impedance of several different audio card outputs set to “Telephones” and “Line Out” modes.

As can be seen from the formula, the absolute values ​​of the measured voltage do not play a role, therefore these measurements can be made long before calibrating the oscilloscope.

Calculation example.

U1 = 6 divisions.

U2 = 7 divisions.

Rx = 30(7 – 6) / 6 = 5 (Ohm).

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How to measure the input impedance of a linear input?

To calculate the attenuator for the linear input of an audio card, you need to know the input impedance of the linear input. Unfortunately, it is impossible to measure the input resistance using a conventional multimeter. This is due to the fact that there are isolation capacitors in the input circuits of audio cards.

The input impedances of different audio cards can vary greatly. So, this measurement will still have to be done.

To measure the input impedance of an audio card using alternating current, you need to apply a sinusoidal signal with a frequency of 50 Hz to the input through a ballast (additional) resistor and calculate the resistance using the given formula.

A sinusoidal signal can be generated in a software low-frequency generator, a link to which is in the “Additional Materials”. Amplitude values ​​can also be measured using a software oscilloscope.

The picture shows the connection diagram.

The voltages U1 and U2 must be measured with a virtual oscilloscope in the corresponding positions of the SA switch. There is no need to know the absolute voltage values, so the calculations are valid until the device is calibrated.

Calculation example.

Rx = 50 * 100 / (540 – 100) ≈ 11.4 (kOhm).

Here are the results of impedance measurements of various line inputs.

As you can see, the input resistances differ significantly, and in one case, almost an order of magnitude.

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How to calculate a voltage divider (attenuator)?

The maximum unlimited amplitude of the audio card input voltage, at the maximum recording level, is about 250 mV. A voltage divider, or as it is also called an attenuator, allows you to expand the range of measured voltages of an oscilloscope.

The attenuator can be constructed using different circuits, depending on the division coefficient and the required input resistance.

Here is one of the divider options that allows you to make the input resistance a multiple of ten. Thanks to the additional resistor Rext. you can adjust the resistance of the lower arm of the divider to some round value, for example, 100 kOhm. The disadvantage of this circuit is that the sensitivity of the oscilloscope will depend too much on the input impedance of the audio card.

So, if the input impedance is 10 kOhm, then the division ratio of the divider will increase tenfold. It is not advisable to reduce the resistor of the upper arm of the divider, since it determines the input resistance of the device, and is the main element in protecting the device from high voltage.

So, I suggest you calculate the divider yourself based on the input impedance of your audio card.

There is no error in the picture; the divider begins to divide the input voltage already when the scale is 1:1. Calculations, of course, need to be done based on the actual ratio of the divider arms.

In my opinion, this is the simplest and at the same time the most universal divider circuit.

An example of divisor calculation.

Initial values.

R1 – 1007 kOhm (result of measuring a 1 mOhm resistor).

Rin. – 50 kOhm (I chose the higher-impedance input of the two available on the front panel of the system unit).

Calculation of the divider in the switch position 1:20.

First, using formula (1), we calculate the division coefficient of the divider, determined by resistors R1 and Rin.

(1007 + 50)/ 50 = 21.14 (times)

This means that the total division ratio in the switch position 1:20 should be:

21.14*20 = 422.8 (times)

We calculate the resistor value for the divider.

1007*50 /(50*422.8 –50 –1007) ≈ 2.507 (kOhm)

Calculation of the divider in the switch position 1:100.

We determine the overall division ratio at the switch position of 1:100.

21.14*100 = 2114 (times)

1007*50 / (50*2114 –50 –1007) ≈ 0.481 (kOhm)

To make calculations easier, take a look at this link: How to pair Notepad with the Windows Calculator to make calculations easier?

If you are going to use only the Avangard oscilloscope and only in the 1:1 and 1:20 ranges, then the accuracy of resistor selection may be low, since the Avangard can be calibrated independently in each of the two available ranges. In all other cases, you will have to select resistors with maximum accuracy. How to do this is written in the next paragraph.

If you doubt the accuracy of your tester, then you can adjust any resistor with maximum accuracy by comparing ohmmeter readings.

To do this, instead of a permanent resistor R2, a tuning resistor R* is temporarily installed. The resistance of the trimming resistor is selected so as to obtain the minimum error in the corresponding division range.

Then the resistance of the trimming resistor is measured, and the constant resistor is already adjusted to the resistance measured by an ohmmeter. Since both resistors are measured with the same device, the ohmmeter error does not affect the measurement accuracy.

And these are a couple of formulas for calculating the classic divisor. A classic divider can be useful when a high input impedance of the device (mOhm/V) is required, but you don’t want to use an additional dividing head.

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How to select or adjust voltage divider resistors?

Since radio amateurs often have difficulty finding precision resistors, I will talk about how you can adjust common resistors for a wide range of applications with high accuracy.

High-precision resistors are only several times more expensive than conventional ones, but on our radio market they are sold for 100 pieces, which makes their purchase not very advisable.

Using trim resistors.

As you can see, each arm of the divider consists of two resistors - a constant one and a trimmer one.

Disadvantage: cumbersome. Accuracy is limited only by the available accuracy of the measuring instrument.

Selection of resistors.

Another way is to select pairs of resistors. Accuracy is ensured by selecting pairs of resistors from two sets of resistors with a large spread. First, all resistors are measured, and then pairs are selected whose sum of resistances most closely matches the circuit.

It was in this way, on an industrial scale, that the divider resistors for the legendary TL-4 tester were adjusted.

The disadvantage of this method is that it is labor intensive and requires a large number of resistors.

The longer the list of resistors, the higher the selection accuracy.

Adjusting resistors using sandpaper.

Even industry does not shy away from adjusting resistors by removing part of the resistive film.

However, when adjusting high-resistance resistors, it is not allowed to cut through the resistive film. For high-resistance film resistors MLT, the film is applied to a cylindrical surface in the form of a spiral. Such resistors must be filed extremely carefully so as not to break the circuit.

Precise adjustment of resistors in amateur conditions can be done using the finest sandpaper - “null sandpaper”.

First, the protective layer of paint is carefully removed from the MLT resistor, which obviously has a lower resistance, using a scalpel.

The resistor is then soldered to the “ends”, which are connected to the multimeter. By careful movements of the “zero” skin, the resistance of the resistor is brought to normal. When the resistor is adjusted, the cut area is covered with a layer of protective varnish or glue.

What a “zero” skin is is written here.

In my opinion, this is the fastest and easiest way, which, nevertheless, gives very good results.

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Construction and details.

The elements of the adapter circuit are housed in a rectangular duralumin housing.

The attenuator division ratio is switched using a toggle switch with the middle position.

The standard CP-50 connector is used as the input jack, which allows the use of standard cables and probes. Instead, you can use a regular 3.5mm Jack audio jack.

Output connector: standard 3.5mm audio jack. The adapter connects to the linear input of the audio card using a cable with two 3.5mm jacks at the ends.

The assembly was carried out using the hinged mounting method.

To use the oscilloscope you will need another cable with a probe at the end.

How to make it is written in detail here.

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How to calibrate a virtual oscilloscope?

To calibrate an oscilloscope, you need to have at least some kind of measuring instrument. Any pointer tester or digital multimeter that you trust will do.

Due to the fact that some testers have too high an error when measuring alternating voltage up to 1 Volt, we perform calibration at the maximum possible voltage, but unlimited in amplitude.

Before calibration, we make the following settings.

Disable the audio card equalizer.

“Line output level”, “WAVE level”, “Line input level” and “Recording level” are set to the maximum gain position. This will ensure repeatability of the result during further measurements.

Having reset the generator settings just in case using Command > Get Generator Default Setting, set the “Gain” (level) to 0db.

We select the generator frequency of 50Hz using the “Frequency Presets” switch, since all amateur instruments for measuring alternating voltage can operate at this frequency, and our adapter cannot yet operate correctly at higher frequencies.

Switch the adapter input to 1:1 mode.

Looking at the oscilloscope screen, use the Trim generator knob to select the maximum unlimited signal level.

The signal may be limited both at the input of the audio card and at its output, and the accuracy of calibration may be significantly reduced. AudioTester even has a special overload indicator, which is highlighted in red in the screenshot.

Using a tester, we measure the voltage at the generator output and calculate the corresponding amplitude value.

Voltmeter reading = 1.43 Volts (rms).

We get the amplitude value.

1.432*√2 = 2.025 (Volts)

The "Options > Calibrate" command brings up the "AudioTester" calibration window.

And although the dimension in “mVrms” is indicated next to the input window, which in theory should mean the root mean square value, in reality, in the “oszi v2.0c” oscilloscope from the “AudioTester” kit, the entered values ​​correspond to... it’s not clear what. Which, however, does not at all prevent you from accurately calibrating the device.

By entering values ​​in small increments, you can precisely adjust the size of the sine wave image to the amplitude value calculated above.

The picture shows that the signal amplitude is a little more than two divisions, which corresponds to 2.02 Volts.

The accuracy of the display of the amplitude of the signals received from the 1:20 and 1:100 inputs will depend on the accuracy of the selection of the corresponding divider resistors.

When calibrating the Avangard oscilloscope, the values ​​obtained during measurement by the tester must also be multiplied by √2, since both the voltmeter and the Avangard calibrator are designed for amplitude values.

Enter the resulting value into the calibration window in millivolts - 2025 and press Enter.

To calibrate the second range of the Avangard oscilloscope, which is marked as “250,” you must first calculate the real division factor by comparing the readings of the built-in voltmeter in two divider ranges: 1:1 and 1:20. The oscilloscope voltmeter should be in the “12.5” position

122 / 2323 = 19,3

Then you need to correct the “calibr” file, which can be opened in Notepad. On the left is the file before editing, and on the right is after.

The "calibr" file is located in the same directory as the current copy of the program.

In the eighth line we enter the real division coefficient corresponding to the divider of the first (left) channel.

If you have built a two-channel adapter, then in the ninth line we make an amendment for the second (right) channel.

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How to equalize the amplitude-frequency response of the adapter?

The linear input of the audio card, and the adapter circuits themselves, have some input capacitance. The reactance of this capacitance changes the division ratio of the divider at high frequencies.

To equalize the frequency response of the adapter in the 1:1 range, you need to select the capacitance of capacitor C1 so that the amplitude of the signal at a frequency of 50 Hz is equal to the amplitude of the signal with a frequency of 18-20 kHz.

Resistors R2 and R3 reduce the influence of the input capacitance and create an increase in the frequency response in the high frequency region. This rise can be compensated by selecting capacitors C2 and C3 in the corresponding ranges of 1:20 and 1:100.

I selected the following capacitances: C1 – 39pF, C2 – 10nF, C3 – 0.1nF.

Now that the Y channel of the oscilloscope's vertical deviation is calibrated and linearized, you can see what certain periodic signals, and more, look like. “AudioTester-e” has “waiting scan synchronization”.

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What to do if there is no tester? Or dangerous experiments.

Can a lighting network be used for calibration?

Since any self-respecting radio amateur, despite all the warnings, the first thing he does is try to get his brainchild into a socket, I considered it necessary to talk about this dangerous activity in more detail.

According to GOST, the network voltage should not go beyond 220 Volts - 10% + 5%, although, in real life, this condition is not met as often as we would like. Measurement errors during resistor fitting and impedance measurements can also introduce high errors with this calibration method.

If you have assembled a precision divider, for example, using high-precision resistors, and if it is known that the voltage in the lighting network in your house is maintained with sufficient accuracy, then it can be used for rough calibration of the oscilloscope.

But, there are a lot of BUTs, because of which I categorically do not recommend you to do this. The first and most important “BUT” is the very fact that you are reading this article. Anyone who doesn't deal with electricity would hardly waste time on this. But, if this is not an argument...

The most important!

1. The computer must be reliably grounded!!!

2. Do not, under any circumstances, stick a ground wire into a socket! This is the wire that is connected through the housing of the linear input connector to the housing of the system unit!!! (Other names for this wire: ground, body, common, screen, etc.) Then, regardless of whether you get into phase or zero, a short circuit will not occur.

In other words, you can only plug into a socket a wire that is connected to a 1 meg resistor R1 located in the adapter circuit!!!

If you try to plug a wire connected to the housing into the network, then in 50% of cases this will lead to the most dire consequences.

Since the maximum unlimited amplitude at the linear input is about 250 mV, then at the 1:100 divider position you will see an amplitude of approximately 50 ... 250 Volts (depending on the input impedance). Therefore, to measure the mains voltage, the adapter must be equipped with a 1:1000 divider.

An example of calculating a divisor of 1:1000.

Upper arm of the divider = 1007 kOhm.

Input impedance = 50kOhm.

Input division ratio 1:1 = 20.14.

We determine the overall division factor for the input to be 1:1000.

21.14*1000 = 21140 (times)

We calculate the resistor value for the divider.

1007*50 / 50*21140 –50 –1007 ≈ 47.7 (Ohm)

Since the input impedance of the adapter when dividing 1:100 is close to 1 mOhm, I did it simpler and used a 1:10 oscilloscope dividing head, which is designed for an input impedance of 1 mOhm. Please note that the input impedance deviation of this professional divider is 10%, which is even higher than that of our toy one.

When using a 1:100 input and a 1:10 head, the total division ratio is 1:1000.

When you see the mains voltage on the screen of the AudioTester oscilloscope, adjust the amplitude to 311 millivolts by selecting the number entered into the form.

Why 311mV?

220V (rms) * √2 = 311V (amplitude)

But, we use a divisor of 1:1000.

311V: 1000 = 311mV

When calibrating the Avangard oscilloscope, select the voltmeter scale “12.5”. When you see the mains voltage on the screen, enter the value 311 into the calibration window. In this case, the Avangard-a voltmeter should begin to show a voltage of 311 mV or close to it.

A small note. The fact is that the voltage shape in modern electrical networks differs from sinusoidal. This is due to the fact that most modern electrical appliances use switching power supplies. The latter “cut” the tops of the sinusoid and actually reduce the amplitude value of the voltage. So, in an amicable way, you need to focus not on the visible curve, but on its “sinusoidal continuation”.

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Additional materials.

Download the software package "AudioTester 1.3", which includes an oscilloscope (275kB).

Download the "AudioTester 2.2" software package, which includes an oscilloscope (4.5 MB).

Download portable software oscilloscope "Avangard" (277kB).

Download the software portable low frequency generator (345kB).

Download the brochure Oscilloscope is your assistant (821kB).

oldoctober.com

DIY oscilloscope from a computer or laptop: diagrams and instructions

Today, often instead of making, for example, an oscilloscope from a computer, most people prefer to simply purchase a USB oscilloscope. But after shopping, you can see that the price of budget oscilloscopes starts at $200. And serious equipment costs many times more. It is for those people who are not satisfied with this price that the easiest way is to make an oscilloscope from a laptop or computer with your own hands.

What to use

The most optimal one today is the Osci program; it has an interface similar to a classic oscilloscope: on the monitor there is a standard grid with which you can measure the amplitude or duration yourself.

One of the disadvantages of this program is that it works a little unstable. During operation, the utility may sometimes freeze, and in order to reset it later, you need to use a specialized TaskManager. But all this is compensated by the fact that the program has a familiar interface and is quite easy to use, and also has a large number of functions that make it possible to make a fully functioning oscilloscope from a computer or laptop.

On a note

It must be said that the package of these programs contains a special low-frequency generator, but its use is undesirable; it tries to completely control the operation of the sound card driver, which causes the sound to turn off. If you decide to try it, make sure you have a restore point or make a backup of your OS. The best way to make an oscilloscope from a computer with your own hands is to download a working generator.

"Vanguard"

This is a domestic program, it does not have the usual and standard measuring grid, and has a very large screen for taking screenshots, but at the same time allows you to use the installed frequency meter and amplitude voltmeter. This partially compensates for the disadvantages mentioned above.

Having made this oscilloscope from a computer, you will encounter the following: at low levels of indicators, a voltmeter and frequency meter can significantly distort the data, but for beginner radio amateurs, this utility will be quite sufficient. Another useful function is that you can do completely independent calibration of the two existing scales of the installed voltmeter.

How to use it

Due to the fact that the input circuits of the sound card have a special isolation capacitor, the computer as an oscilloscope can only work with a closed input. Thus, only the variable component of the indicators will be visible on the monitor, but with some skill, using these programs you can measure the indicator with a constant component. This is very important in the case when, for example, the counting time of a multimeter does not make it possible to record a certain value of the voltage amplitude on a capacitor charged using a large resistor.

The lower voltage value is limited by background and noise levels and is approximately 1 mV. The upper limit is limited only by the indicators of the divider and reaches more than a hundred volts. The frequency range is limited by the sound card itself and for older computers is about 20 kHz.

Naturally, in this case a rather primitive device is considered. But when you do not have the opportunity, for example, to use a USB oscilloscope, then in this case its use is quite acceptable. This device will help you in repairing various audio equipment, or can be used for educational purposes. In addition, the oscilloscope program will allow you to save the plot to illustrate the material or for posting on the network.

Electrical diagram

If you need an attachment to your computer, then making an oscilloscope will be much more difficult. Today on the Internet you can find quite a large number of different circuits for these devices, and to make, for example, a two-channel oscilloscope, you will only need to duplicate them. The second channel is often relevant when it is necessary to compare two signals or an oscilloscope is used to connect external synchronization.

As a rule, the circuits are very simple, but this way, you will independently provide a very large range of available measurements using a minimum of radio components. Moreover, the attenuator, which is manufactured according to the classical scheme, would require you to have highly specialized high-ohm resistors, and its input resistance changed all the time when switching the range. Therefore, you would experience some limitations when using conventional oscilloscope leads, which are rated for input impedances of no more than 1 mOhm.

How to choose voltage divider resistors

Due to the fact that radio amateurs often have difficulty selecting precision resistors, it often happens that they have to choose wide-profile devices that must be adjusted as precisely as possible, otherwise it will not be possible to make an oscilloscope from a computer with your own hands.

Voltage divider trimmer resistors

In this case, each arm of the divider has two resistors, one is constant, the second is tuning. The disadvantage of this option is its bulkiness, but the accuracy is limited only by what available characteristics the measuring apparatus has.

How to choose regular resistors

Another option to make an oscilloscope from a computer is to select pairs of resistors. Accuracy in this case is ensured due to the fact that pairs of two sets with a fairly decent spread are used. It is important to initially carry out careful measurements of all devices, and then select pairs whose total resistance will be most suitable for your circuit.

Resistor adjustment

Today, adjusting resistors by removing part of the film is often used even in modern industry, that is, an oscilloscope is often made from a computer.

But it must be said that if you want to customize high-resistance resistors, then the resistive film should not be cut all the way through. Since in these devices it is located on a cylindrical surface in the form of a spiral, therefore the undercut must be made extremely carefully to prevent the chain from breaking. Then:

After, when the resistor is completely adjusted, the cut area is covered with a layer of special protective varnish.

Today this method is the fastest and simplest, but at the same time it gives good results, which made it optimal for home use.

Things to consider

There are a number of rules that must be followed in any case if you decide to carry out this work:

• The computer used for the oscilloscope must be grounded.
• Do not connect the ground to the outlet. It is connected through a special linear input connector housing to the system unit housing. In this case, no matter whether you hit phase or zero, you will not have a short circuit.

In other words, only the wire that connects to the resistor can be connected to the socket and is located in the adapter circuit with a nominal value of one megohm. If you try to connect a wire that is in contact with the housing into the network, then in almost all cases this will certainly lead to the most disastrous consequences.

elektro.guru

Program “Computer – oscilloscope”

Digital Oscilloscope V3.0 is a popular amateur radio program that will turn your computer into a virtual oscilloscope

Good afternoon, dear radio amateurs! Welcome to the website “Amateur Radio”

Today on the site we will look at a simple amateur radio program that turns a home computer into an oscilloscope.

There are two ways to turn a personal computer into an oscilloscope. You can buy or make a set-top box that connects to your PC. The set-top box will be an ADC, software-controlled. And install the appropriate program on your PC. But this is a costly method. The second method is cost-free; any PC already has an ADC and a DAC - a sound card. Using it, you can convert your computer into a simple low-frequency oscilloscope, just by installing software, and you will have to solder a simple input divider. There are quite a few such programs. Today we will look at one of them – Digital Oscilloscope V3.0.

Digital Oscilloscope V3.0 (149.8 KiB, 49,025 hits)

After starting the program, a window will appear on the screen that looks very similar to a regular oscilloscope. The linear input of the sound card is used to supply the signal. You usually need to apply a signal of no more than 0.5-1 volt to the input, otherwise a limitation occurs, so you need to solder the input divider according to a simple circuit, as shown in Figure No. 2.

KD522 diodes are needed to protect the sound card input from too much signal. After connecting the circuit and input signal, you need to turn on the oscilloscope. To do this, click the RUN field with the mouse and select START or click the triangle in the second row from the top of the window. The oscilloscope will show the signal. The frequency and period of the signal will be displayed in the lower right corner of the screen. But the voltage shown by the oscilloscope may not correspond to reality. When setting up an input divider, you need to try to set the division coefficient with a variable resistor so that the voltage shown on the screen is as realistic as possible.

Purpose of governing bodies. TIME/DIV – time/division; TRIGGER – synchronization; CALIB – level; VOLT/DIV – voltage/division. And one more advantage of this program is that the oscilloscope has a memory - you can stop the work, and an oscillogram will remain on the screen, which can be saved in the PC memory or printed.

Before calibration, we make the following settings.

Disable the audio card equalizer.
“Line Out Level”, “WAVE Level”, “Line In Level” and “Recording Level” are set to the maximum gain position. This will ensure repeatability of the result during further measurements.
Having reset the generator settings just in case using Command > Get Generator Default Setting, set the “Gain” (level) to 0db.
We select the generator frequency of 50Hz using the “Frequency Presets” switch, since all amateur instruments for measuring alternating voltage can operate at this frequency, and our adapter cannot yet work correctly at higher frequencies. Switch the adapter input to 1:1 mode .
Looking at the oscilloscope screen, use the Trim generator knob to select the maximum unlimited signal level.
The signal may be limited both at the input of the audio card and at its output, and the accuracy of calibration may be significantly reduced. AudioTester even has a special overload indicator, which is highlighted in red in the screenshot.
Using a tester, we measure the voltage at the generator output and calculate the corresponding amplitude value.
Example.
Voltmeter reading = 1.43 Volts (rms).
We get the amplitude value.
1.432*√2 = 2.025 (Volts)
The “Options > Calibrate” command brings up the “AudioTester” calibration window.
And although the dimension in “mVrms” is indicated next to the input window, which in theory should mean the root mean square value, in reality, in the “oszi v2.0c” oscilloscope from the “AudioTester” kit, the entered values ​​correspond to... it’s not clear what. Which, however, does not at all prevent you from accurately calibrating the device.
By entering values ​​in small increments, you can precisely adjust the size of the sine wave image to the amplitude value calculated above.
The picture shows that the signal amplitude is a little more than two divisions, which corresponds to 2.02 Volts.
The accuracy of the display of the amplitude of the signals received from the 1:20 and 1:100 inputs will depend on the accuracy of the selection of the corresponding divider resistors.
When calibrating the Avangard oscilloscope, the values ​​obtained during measurement by the tester must also be multiplied by √2, since both the voltmeter and the Avangard calibrator are designed for amplitude values.
Enter the resulting value into the calibration window in millivolts - 2025 and press Enter.
To calibrate the second range of the Avangard oscilloscope, which is marked as “250,” you must first calculate the real division factor by comparing the readings of the built-in voltmeter in two divider ranges: 1:1 and 1:20. The oscilloscope voltmeter should be in the “12.5” position

Example.
122 / 2323 = 19,3
Then you need to correct the “calibr” file, which can be opened in Notepad. On the left is the file before editing, and on the right is after.
The "calibr" file is located in the same directory as the current copy of the program.
IN eighth line we enter the real division coefficient corresponding to the divider of the first (left) channel.
If you have built a two-channel adapter, then ninth line we make a correction for the second (right) channel. How to equalize the amplitude-frequency response of the adapter? The linear input of the audio card, and the adapter circuits themselves, have some input capacitance. The reactance of this capacitance changes the division ratio of the divider at high frequencies. To equalize the frequency response of the adapter in the 1:1 range, you need to select the capacitance of capacitor C1 so that the amplitude of the signal at a frequency of 50 Hz is equal to the amplitude of the signal with a frequency of 18-20 kHz. Resistors R2 and R3 reduce the influence of the input capacitance and create an increase in the frequency response in the high frequency region. This rise can be compensated by selecting capacitors C2 and C3 in the corresponding ranges of 1:20 and 1:100.
I selected the following capacitances: C1 – 39pF, C2 – 10nF, C3 – 0.1nF. Now that the Y channel of the oscilloscope's vertical deviation is calibrated and linearized, you can see what certain periodic signals, and more, look like. “AudioTester-e” has “waiting scan synchronization”. What to do if there is no tester? Or dangerous experiments. Can a lighting network be used for calibration?

Since any self-respecting radio amateur, despite all the warnings, the first thing he does is try to get his brainchild into a socket, I considered it necessary to talk about this dangerous activity in more detail.
According to GOST, the network voltage should not go beyond 220 Volts - 10% + 5%, although, in real life, this condition is not met as often as we would like. Measurement errors during resistor fitting and impedance measurements can also introduce high errors with this calibration method.
If you have assembled a precision divider, for example, using high-precision resistors, and if it is known that the voltage in the lighting network in your house is maintained with sufficient accuracy, then it can be used for rough calibration of the oscilloscope.
But, there are a lot of BUTs, because of which I categorically do not recommend you to do this. The first and most important “BUT” is the very fact that you are reading this article. Anyone who doesn't deal with electricity would hardly waste time on this. But, if this is not an argument... The most important!
1. The computer must be reliably grounded!!!
2. Do not, under any circumstances, stick a ground wire into a socket! This is the wire that is connected through the housing of the linear input connector to the housing of the system unit!!! (Other names for this wire: ground, body, common, screen, etc.) Then, regardless of whether you get into phase or zero, a short circuit will not occur.
In other words, you can only plug into a socket a wire that is connected to a 1 meg resistor R1 located in the adapter circuit!!!
If you try to plug a wire connected to the housing into the network, then in 50% of cases this will lead to the most dire consequences.
Since the maximum unlimited amplitude at the linear input is about 250 mV, then at the 1:100 divider position you will see an amplitude of approximately 50 ... 250 Volts (depending on the input impedance). Therefore, to measure the mains voltage, the adapter must be equipped with a 1:1000 divider.
The 1:1000 divisor can be calculated by analogy with the 1:100 divisor.
An example of calculating a divisor of 1:1000.
Upper arm of the divider = 1007 kOhm.
Input impedance = 50kOhm.
Input division ratio 1:1 = 20.14.
We determine the overall division factor for the input to be 1:1000.
20.14*1000 = 20140 (times)
We calculate the resistor value for the divider.
1007*50 / 50*20140 –50 –1007 ≈ 50 (Ohm)TO BE CONTINUED:
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It's no secret that beginning radio amateurs don't always have expensive measuring equipment at hand. For example, an oscilloscope, which even on the Chinese market, the cheapest model costs about several thousand.
Sometimes an oscilloscope is needed to repair various circuits, check amplifier distortion, adjust audio equipment, etc. Very often, a low-frequency oscilloscope is used to diagnose the operation of sensors in a car.
In this case, a simple oscilloscope made from your personal computer will help you. No, your computer will not have to be disassembled and modified in any way. All you need to do is solder the console - a divider - and connect it to the PC via the audio input. And to display the signal, install special software. In just a couple of tens of minutes you will have your own oscilloscope, which may well be suitable for analyzing signals. By the way, you can use not only a desktop PC, but also a laptop or netbook.
Of course, such an oscilloscope is hardly comparable to a real device, since it has a small frequency range, but it is a very useful thing in the household for viewing the output of an amplifier, various ripples of power supplies, etc.

Set-top box diagram

Assembling the console

Software

(downloads: 8310)