An oscilloscope is a portable device that is designed for testing microcircuits. Additionally, many models are suitable for industrial control and can be used for a variety of measurements. You cannot make an oscilloscope with your own hands without a zener diode, which is its main element. This part is installed in devices of varying power.

Additionally, depending on the modification, devices may include capacitors, resistors and diodes. The main parameters of the model include the number of channels. Depending on this indicator, the maximum bandwidth changes. Also, when assembling an oscilloscope, you should consider the sampling rate and memory depth. In order to analyze the received data, the device is connected to a personal computer.

Circuit of a simple oscilloscope

The circuit of a simple oscilloscope includes a 5 V zener diode. Its throughput depends on the types of resistors that are installed on the chip. To increase the amplitude of oscillations, capacitors are used. You can make a probe for an oscilloscope with your own hands from any conductor. In this case, the port is selected separately in the store. Resistors of the first group must withstand a minimum resistance in the circuit of 2 ohms. In this case, the elements of the second group should be more powerful. It should also be noted that there are diodes on the circuit. In some cases they form bridges.

Single channel model

You can make a single-channel digital oscilloscope with your own hands only using a 5 V zener diode. Moreover, more powerful modifications are unacceptable in this case. This is due to the fact that an increased maximum voltage in the circuit leads to an increase in the sampling frequency. As a result, the resistors in the device fail. Capacitors for the system are selected only of the capacitive type.

The minimum resistance of the resistor should be 4 ohms. If we consider the elements of the second group, then the transmission parameter in this case should be 10 Hz. In order to increase it to the desired level, various types of regulators are used. Some experts recommend using orthogonal resistors for single-channel oscilloscopes.

In this case, it should be noted that they raise the sampling rate quite quickly. However, there are still negative aspects in such a situation, and they should be taken into account. First of all, it is important to note the sharp excitation of vibrations. As a result, signal asymmetry increases. Additionally, there are problems with the sensitivity of the device. Ultimately, the accuracy of the readings may not be the best.

Dual Channel Devices

Making a two-channel oscilloscope with your own hands (the diagram is shown below) is quite difficult. First of all, it should be noted that zener diodes in this case are suitable for both 5 V and 10 V. In this case, capacitors for the system must be used only of a closed type.

Due to this, the device’s bandwidth can increase to 9 Hz. Resistors for the model are usually used of the orthogonal type. In this case, they stabilize the signal transmission process. To perform addition functions, microcircuits are mainly selected from the MMK20 series. You can make a divider for an oscilloscope with your own hands from a regular modulator. It's not particularly difficult.

Multi-channel modifications

In order to assemble a USB oscilloscope with your own hands (the diagram is shown below), you will need a fairly powerful zener diode. The problem in this case is increasing the throughput of the circuit. In some situations, the operation of resistors may be disrupted due to a change in the limiting frequency. In order to solve this problem, many use auxiliary dividers. These devices greatly help to increase the threshold voltage limit.

You can make a divider using a modulator. Capacitors in the system must be installed only near the zener diode. To increase the bandwidth, analog resistors are used. The negative resistance parameter fluctuates on average around 3 ohms. The blocking range depends solely on the power of the zener diode. If the limiting frequency drops sharply when the device is turned on, the capacitors must be replaced with more powerful ones. In this case, some experts recommend installing diode bridges. However, it is important to understand that the sensitivity of the system in this situation deteriorates significantly.

Additionally, it is necessary to make a probe for the device. To ensure that the oscilloscope does not conflict with a personal computer, it is more advisable to use an MMP20 type microcircuit. You can make a probe from any conductor. Ultimately, a person will only have to buy a port for him. Then, using a soldering iron, the above elements can be connected.

Assembling a 5 V device

At 5 V, a do-it-yourself oscilloscope attachment is made only using an MMP20 type microcircuit. It is suitable for both ordinary and powerful resistors. The maximum resistance in the circuit should be 7 ohms. In this case, the bandwidth depends on the signal transmission speed. Dividers for devices can be used in a variety of types. Today, static analogues are considered more common. The bandwidth in this situation will be around 5 Hz. To increase it, it is necessary to use tetrodes.

They are selected in the store based on the limiting frequency parameter. To increase the amplitude of the reverse voltage, many experts advise installing only self-regulating resistors. In this case, the signal transmission speed will be quite high. At the end of the work, you need to make a probe to connect the circuit to a personal computer.

10V Oscilloscopes

A do-it-yourself oscilloscope is made with a zener diode, as well as closed-type resistors. If we consider the device parameters, the vertical sensitivity indicator should be at the level of 2 mV. Additionally, the bandwidth must be calculated. To do this, the capacitance of the capacitors is taken and correlated with the maximum resistance of the system. Resistors for the device are most suitable of the field type. To minimize the sampling frequency, many experts advise using only 2 V diodes. Due to this, high signal transmission speeds can be achieved. In order for the tracking function to be performed quite quickly, the microcircuits are installed like MMP20.

If you plan storage and playback modes, you must use a different type. Cursor measurements will not be available in this case. The main problem with these oscilloscopes can be considered a sharp drop in the limiting frequency. This is usually due to the rapid expansion of data. The problem can be solved only with the use of a high-quality divider. At the same time, many also rely on a zener diode. You can make a divider using a conventional modulator.

How to make a 15 V model?

Assembling an oscilloscope with your own hands using linear resistors. They can withstand a maximum resistance of 5 mm. Due to this, there is not much pressure on the zener diode. Additionally, care should be taken when choosing capacitors for the device. For this purpose, it is necessary to measure the threshold voltage. Experts use a tester for this.

If you use tuning resistors for an oscilloscope, you may encounter increased vertical sensitivity. Thus, the data obtained due to testing may be incorrect. Considering all of the above, it is necessary to use only linear analogues. Additionally, care should be taken to install the port, which is connected to the microcircuit via a probe. In this case, it is more expedient to install the divider through the bus. To prevent the oscillation amplitude from being too large, many advise using vacuum-type diodes.

Using PPR1 series resistors

Making a USB oscilloscope with your own hands using these resistors is not an easy task. In this case, it is necessary first of all to evaluate the capacitance of the capacitors. To ensure that the maximum voltage does not exceed 3 V, it is important to use no more than two diodes. Additionally, you should remember the nominal frequency parameter. On average this figure is 3 Hz. Orthogonal resistors are not uniquely suitable for such an oscilloscope. Construction changes can only be made using a divider. At the end of the work, you need to do the actual installation of the port.

Models with PPR3 resistors

You can make a USB oscilloscope with your own hands using only grid capacitors. Their peculiarity is that the level of negative resistance in the circuit can reach 4 ohms. A wide variety of microcircuits are suitable for such oscilloscopes. If we take the standard version of the MMP20 type, then it is necessary to provide at least three capacitors in the system.

Additionally, it is important to pay attention to the density of the diodes. In some cases, this affects the bandwidth. To stabilize the division process, experts advise carefully checking the conductivity of the resistors before turning on the device. Lastly, the regulator is directly connected to the system.

Devices with vibration suppression

Oscilloscopes with an oscillation suppression unit are used quite rarely these days. They are most suitable for testing electrical appliances. Additionally, their high vertical sensitivity should be noted. In this case, the limiting frequency parameter in the circuit should not exceed 4 Hz. Due to this, the zener diode does not overheat significantly during operation.

You can make an oscilloscope yourself using a grid-type microcircuit. In this case, it is necessary to decide on the types of diodes at the very beginning. Many people in this situation advise using only analog types. However, in this case, the signal transmission speed may be significantly reduced.

There are various instructions on the Internet for turning an old (sometimes partially non-working) TV into a widescreen oscilloscope. This article will also tell you how to create a decent electronic device using simple modifications for a total cost of about $20. In order for the input signal to be displayed on the screen and reproduced through the TV speaker, you will need to assemble a simple device that switches the power supply circuit of the deflection system. Of course, you cannot stretch out a large frequency spectrum with such a device (actually 20-20,000 kHz), but monitoring low-frequency oscillations is quite accessible.
You can also install the main connectors and controls of the device into the television case (fortunately, the space allows this). For example, the presence of an RCA connector will be an excellent way to connect an iPod and at the same time allow the supply of alternating voltage signals from millivolts to hundreds of volts. Nearby you can place a 1 mOhm trimmer and a 6-section rotary switch. A small trimmer will be convenient to control the horizontal scanning frequency, and a bright red button is suitable for turning on the device.

It remains to add that this connection diagram is not suitable for all TV models and is more useful for people who know how to handle circuitry and have experience in electronics. But the idea itself contains many interesting points.

Safety requirements

The implementation of the described project involves carrying out work near an open television transformer and high-voltage capacitors. The voltage at the magnetron reaches 120 kV! To eliminate the possibility of fatal electrical shock, proper safety precautions must be strictly followed. The first step to performing any action should be to completely de-energize the device. Here we must not forget about high-voltage capacitors. Therefore, the protective casing of the high-voltage unit is removed extremely carefully. It is important not to damage the wires of the printed circuit board or touch its exposed contacts.

Next, you need to forcefully discharge large capacities (50 V or more). This is done with a well-insulated screwdriver or tweezers. Their contacts are closed to each other or to the housing until completely discharged. You should not do this on a printed circuit board, as the tracks may burn out. When performing work or testing the device, make sure that someone close to you is nearby who can call a doctor or provide first aid.

Principle of operation

Cathode ray tube (CRT) televisions and oscilloscopes are considered the most interchangeable devices. Also, a television receiver is more complex than a basic laboratory oscilloscope. To remake it, it is enough to get rid of some of the TV functions built into it and add a simple amplifier. After all, each unfolded line of the TV screen is created by an electron beam, quickly scanned through the transparent material of the luminescent substrate of the tube.

The charged electrons are controlled by electric and magnetic fields created by coils located behind the tube. These wire cores deflect the beam horizontally and vertically, controlling the placement of the image on the screen. To adjust it to the center of the oscilloscope line, it is necessary to make some modifications to them.

Let us remember that the video signal produces 32 frames per second, each of which consists of two “interlaced” images (that is, 64 frames are scanned). The NTSC standard defines 525 lines in the screen format, other standards have slightly different values. This means that to reproduce a filled picture on the screen, the electron beam must be deflected vertically every 1/64 seconds (frequency 64 Hz), and horizontally 1/(64x525) seconds (frequency 32000 Hz). To ensure such values, the voltage of the line transformer exceeds 15,000 volts. In this case, the device works like a TV and creates a detailed image on the screen.

To get it to draw an image on a very thin line vertically deflected by the input signal, you need to adjust the number of turns of the screen coils. It is also important to “work” with the inductor coil. Its impedance depends on frequency. The higher the frequency, the more difficult it will be to display it on the screen. With an outer diameter of the toroidal core of 10 mm and a thickness of 2 mm, windings I and III should each contain 100 turns of PELSHO 0.1 wire, and winding II should contain 30 turns.

It’s also worth remembering that the signal on a TV is mathematically integrated. This causes the input square wave to appear as a triangle wave on the screen, and the input triangle wave as a sine wave. This only applies to the image, not the sound. Sine waves will be displayed without distortion. The phenomenon will not be as noticeable on very old TVs that are capable of displaying white noise or a blue screen when there is no signal, rather than automatically turning off the image.

Removing unnecessary nodes

In our case, we used an old television receiver with a 15-inch screen and a classic UHF/VHF tuner. It is not required to create an oscilloscope, so you can immediately remove the tuner and forget about its existence. You can also gradually disconnect unnecessary modules one by one, checking that the TV can still function. You only need the main board and everything connected to the kinescope. It is necessary that it only displays white noise or a blue screen. You can simply empty the box of the remaining parts.

The TV being converted had two potentiometers on the front. One of them served to turn on and adjust the volume, and the other controlled the brightness. Both were removed: the first was replaced with a power switch (big red button), the second had to be set to maximum brightness and fixed by soldering additional resistors into the circuit. You should immediately note that a device with a built-in volume control is not suitable for modification. It amplifies the signal attached to the television and you will have to look for an amplifier on the main board, and this will cause additional problems. The speakers can also be turned off at this stage.

Preparing the deflection system

To achieve an oscilloscope image on the kinescope screen, you will need to apply the generated amplified signal of vertical and horizontal sync pulses to the deflection coils H and V. How to obtain it will be discussed a little later, but now it is necessary to prepare the deflection system. The coils are connected to the main board with four pins. You need to disconnect the horizontal one, the red and blue wires go to it. By connecting an iPod or computer directly to these terminals, you can display music on the kinescope screen. The vertical coil has a yellow and orange wire, but to get a 64Hz scan they need to be switched to the horizontal coil.

Now you need to find where the coils connect to the small circuit board on the picture tube tube. If the television receiver is not very new, there are only two coils and 4 wires go from them to the main board. Otherwise, there will be more coils and the modification will not work in this form. But don’t give up what you started, and you can experiment a little. For now, we will assume that there are still 4 wires. It remains to deal with the wires going to the kinescope. According to the right-hand rule (F=qVxB), we remove one of them in random order. If, when you turn on the device, a horizontal line is displayed on the screen, the vertical coil is disabled; if it is vertical, then vice versa. The corresponding ends are found by the tester and marked.

The horizontal coil connection wires are now removed from the main PCB. Do not forget that you will have to deal with a frequency of 30,000 Hz and a voltage of more than 15,000 volts. The future oscilloscope does not need them. Before touching, they must be short-circuited, then well insulated and placed inside the case so that they do not touch anything after turning on the device. So, the 60 Hz vertical marking line is ready. To obtain the same horizontal line of 60 Hz, we solder the two remaining wires going to the vertical coil to the horizontal one. And the vertical one will become the input of the oscilloscope for connecting the amplifier circuit.

Sweep setting

The further part of the work is the most dangerous, since it will be performed with the voltage connected. Be especially careful! We try to connect the signal source to the vertical deflection coil (this could be an MP3 player or a computer headphone output). To display one frequency on the screen, try to generate a consistent tone. With the TV turned on, use an insulated screwdriver to carefully touch the high-voltage wires one by one, finding out what changes on the screen this will lead to (your assistant should watch this or use a large mirror).

One of them will affect the scanning frequency. On the board where it enters, you need to solder a trimmer resistance (approximately 50-60 kOhm). After making sure that the unit is working, you can remove the handle of the involved resistor from the device body. Even an impeccably executed horizontal frequency tuning will not allow you to see the upper range, but will only display the scroll waveform on the screen. You can also customize the existing ring tabs located around the narrow part of the kinescope tube. They are usually black or dark gray in color and also indirectly control the final image.

Incoming signal amplification

Everything that has been done up to this point has allowed us to create a good input signal visualizer. It is enough to connect the iPod socket to the vertical deflection coil and the sounding music will be displayed on the screen. But to get a real oscilloscope, you will need an additional amplifier (you can assemble it where the discarded UHF/VHF tuner was located). His idea was borrowed from several thematic sites in order to obtain minimum cost and maximum efficiency. The design of Pavel Falstad was taken as the basis, and the presented printed circuit board is a modified circuit of a push-pull audio amplifier.

To implement it we will need: a TL082 microassembly, including 2 op-amps, a pair of transistors (for example, 41NPN/42PNP), an LM317 power regulator, a Pole rotary switch, a 1 mOhm potentiometer, two 10 kOhm trimers, 4 1A diodes, a transformer for 30 VAC, 1000 µF 50 V electrolyte, two 470 µF 16 V electrolytes and 5 resistors (10 Ohm, 220 Ohm, 1 kOhm, 100 kOhm and 10 mOhm).

The first op-amp controls the gain of the input signal using the formula R1/R2, where R1 is the resistance selected by the rotary switch, R2 is the 1 mOhm pot. Theoretically, it is capable of amplifying the input signal up to 1 million times (with a minimum of 1 ohm present on the rotary switch). The second monitors that the transistors receive the necessary voltage to open the junctions and compensates for distortions. They need 0.7 V to open and 1.4 V to switch.

The finished circuit requires mandatory calibration. The power regulator is designed for a difference of 30 V, so the op amp will typically output +15/-15 V, but for good filtering its output should be a few volts lower than the voltage across the 1000 uF capacitor. For this purpose, there is trimmer 1. The output of the circuit is connected to the horizontal deflection coil. Music passed through the circuit begins to be “cut off” at the top/bottom. To avoid this, trimmer 2 is adjusted until the tops of the clips touch the edges of the screen. This will lower the voltage and prevent the transistors from overloading the RF path of the device (burning the deflection coil).

Now you can connect the built-in speaker system to the TV output. If the volume is excessive, a large load resistance is added (for example, 10 Ohm 1 W); if there is insufficient sound, the load resistance is placed on the deflection coil, after which the latter is recalibrated. To protect yourself from unnecessary annoying beeps while scanning for the desired input signal, you can install a switch on the speaker.

Putting it all together

An additional amplifier can generate a strong magnetic field, so it is worth taking care of its design. The board should be made as compact as possible, with short leads and good grouping. It does not require special shielding, but to avoid interference with other TVs in your home, make sure that it is located in the case without creating interference to the main components. As a last resort, you can use a wooden or plastic case covered with foil on the inside.

In the TV being disassembled, when removing the analog tuner, enough space was freed up to install a transformer with such a board, and there was even a hole for the power switch. It is also advisable to shield the transformer so as not to create interference on TV channels. Connect the terminals for connecting the synchronization voltage and the signal under study to the board only with a shielded wire.

After connecting the transformer to the circuit, connect S1 and S2 respectively, run the input wires through the hole in the body of the television receiver, connect the output of the circuit to the speaker and deflection coil. A minimum wire length should be used in all connections made to reduce leaky loop inductance. All that remains is to find a convenient place to install S1 and S2, close the back cover and start the test drive.

Checking the functionality of the device

In terms of functionality, the assembled oscilloscope is far from worthy laboratory models, but is indispensable for use in simple projects where you need to see the waveform. Also a certain novelty is the ability to hear the signal being studied, especially when receiving feedback that resembles “signs”. In the example under consideration, one can observe a change in the signal induced by a conventional wire coil when it is located in an arbitrary location, above the internal transformer of the device and when it is located above the laptop processor.

The ability to amplify the incoming signal is a great feature if you don't need it to be absolutely precise. The 60 Hz noise amplified by the circuit can still be detected with reasonable accuracy. But this phenomenon is also caused by the stray inductance of the input wire. Only shielded grounding of all parts of the circuit can reduce interference.

The demonstrated coil of wire connected to the input of the device allows the use of large inductance with high amplification. It can detect power sources several meters away by pointing the coil towards the location of the transformers, and then visually view their operation. You can also detect the location of the processor inside a complex device. You can use the coil as an inductive microphone by placing it near a speaker playing music. The magnetic field reproduced by the speaker coil will be detected and amplified by the created device, after which the music being played will be reflected on the oscilloscope kinescope.

You can clearly view the operation of the Internet channel on the device. A dedicated home line (120 VAC) was used as an input signal for this, and, having shown its “picture”, the device still works.

Homemade measuring instruments

Assemble an oscilloscope Only the most experienced can do it in their home workshop. There are many reasons for this: the complexity of the electronic circuit, scarce parts, a large amount of work... The industry, however, produces two or three models for radio amateurs, but they are quite expensive, and they are rarely available in stores.

We offer a simple attachment with which you can turn your TV into a simple oscilloscope. In this case, you do not have to make any changes to the TV circuit; you just need to connect the output of the set-top box to the antenna input of the TV, and an image of the signal being studied will appear on the screen.

Diagram of the oscilloscope attachment

Let's now get acquainted with the basic principles of operation of the oscilloscope attachment. Using a blocking generator and a pulse shaper, the set-top box produces vertical and horizontal sync pulses. When added together, they form a complete television image signal. When the signal under study is supplied to the output of the set-top box, its periodically changing voltage controls the illumination of individual segments of the raster lines. Thus, the set-top box generates a complete television video signal with a picture, which is then fed to the input of the VHF generator and modulates its radiation in frequency. The generator itself operates in the range of the second television channel, so if the output of the set-top box is connected to the antenna input of a television set tuned to the same channel, an image of the signal being studied will appear on the screen.

As you have already noticed, two voltages are supplied to the input of the set-top box - the test signal Usign and an alternating voltage of 6.3 V synchronizing frame scan with a frequency of 50 Hz. It can be removed from the filament winding of any network transformer or from a special additional winding of the transformer of the set-top box power supply.

An alternating voltage with a frequency of 50 Hz is supplied to a pulse shaper made on transistors VT6 and VT7. Transistor VT6 forms a voltage amplification stage. As soon as the amplitude of the synchronizing voltage exceeds a certain level, the transistor enters saturation mode and turns off, i.e., it operates simultaneously in two modes - amplification and switching. Then, through a differentiating chain of capacitor C11 and resistor R13, the synchronization voltage is supplied to the base of transistor VT7, which generates frame sync pulses according to the television standard.

Horizontal sync pulses are generated by a transistor blocking generator based on a VT8 transistor with inductive positive feedback. The sawtooth shape of the horizontal sync pulses is obtained due to the periodic process of charge-discharge of capacitor C13, connected to the circuit of winding II of the blocking transformer T1. From it, horizontal sync pulses through resistor R19 and capacitor C15 are supplied to the base of transistor VT3.

The signal under study is amplified by cascades on transistors VT1, VT2 and VT3. The high gain of these stages is determined by the values ​​of resistor R3 and capacitor C3, which are included in the positive feedback circuit. The periodically changing voltage of the signal under study controls the brightness of the illuminated lines - as if simulating horizontal sync pulses. Transistor VT4 is connected according to the emitter follower circuit and works as a current amplifier.

The complete television image signal generated by the set-top box is fed to the input of a VHF generator assembled on a VT5 transistor, which models it by frequency. The output signal of the set-top box is removed from the voltage divider from resistors R9 and R10. With the component ratings indicated in the diagram, this VHF generator operates in the frequency range of the second television channel of meter waves.

The set-top box is powered by a stabilized 12 V voltage source, which can be used as the power supply described in Appendix No. 2 for 1987. However, it can be assembled according to a simplified scheme (see Fig. 4), using a TVK series transformer. Zener diode VD1 sets the stabilization voltage, which is supplied to the base of the powerful transistor VT1, operating in current amplifier mode. Resistor R1 sets the base current, and capacitor C2 “white” filters the output voltage.

Instead of the D814D zener diode, you can use D813 or KS512 with any letter index. The transistor can be replaced with any other n-p-n with a rated power dissipation of at least 1 W. The power supply is mounted on a printed circuit board or breadboard. Mount transistor VT1 on a radiator with a total area of ​​15-20 cm 2.

The circuit of the set-top box itself is mounted on a printed circuit board with PCB foil on one side or getinax. The location of printed conductors is shown in Figure 2, and the radio components on the board are shown in Figure 3.

Wind transformer T1 on a ring ferrite core measuring 10x14x2 mm. Winding I contains 100 turns, II - 35, and III - 90 turns of PEL-0.1 wire. The procedure for winding a transformer can be simplified if the ferrite core is first carefully split into two parts, windings are wound on them, and then glued with BF-2 or Moment glue. Coil L1 of the oscillating circuit of the VHF generator contains only 6 turns of copper wire in an enamel shell 0.6-0.8 mm thick and is wound on a plastic frame with a ferrite core, for example, from the circuits of an old TV.

Transistors VT1-VT8 - KT315, diodes VD1-VD6 - KD522.

The printed circuit board of the set-top box must be placed in a housing made of shielding material - brass or aluminum, connecting the common wire to the housing.

If the case is made of wood or plastic, glue its inner surface with copper or aluminum foil and connect it to the common wire of the circuit.

On the front panel of the case, place the terminals for connecting the synchronization voltage and the signal under study. They can only be connected to the board with a shielded wire.

The capabilities of the console will expand significantly if you carry out the following modification. For example, if you replace the resistor with another one with a resistance of 50 Ohms, and connect a variable resistance of 100 Ohms in series with it, you can adjust the amplitude of the output television signal of the set-top box. By changing the resistance of resistors R15 and R8, you can control the image size vertically and horizontally.

The output of the set-top box is connected to the antenna socket of the TV only with a coaxial cable of the RK-75 type. Solder its braids to the common wire bus. After soldering, the cable itself must be secured to the board using clamps made of tin or aluminum. For ease of connection, you can solder an antenna plug to the coaxial cable.

When all the parts are installed on the board and soldered, carefully check the correct installation, paying special attention to the gaps between the current-carrying tracks of the board. If bridges from solder drips have formed between them, they must be carefully removed using rosin flux or simply scratched with a sharp awl. And if everything is in order, you can start testing.

The sensitivity of the set-top box is such that the maximum range of the image on the screen is obtained when the amplitude of the signal under study is about 0.3 V. And in order to study signals of larger amplitude, you will have to make an attenurator (attenuator) based on a simple voltage divider. The formulas and diagram in Figure 5 will help you calculate it correctly. To study weak signals, you can connect a sensitive ULF with an emitter follower to the input.

Yours will come in handy homemade oscilloscope and to measure the voltage of the signal under study. In order to turn the set-top box into a voltmeter, just attach a scale grid to the screen. It can be made from a sheet of plexiglass, and the lines can be drawn with a compass needle. For clarity, color the scratched grooves with a black or brown felt-tip pen. Remains of paint from the surface of plexiglass can be easily removed with a cotton swab dipped in cologne. When the grid is ready, apply a voltage with a known amplitude to the input of the console and fix its value on the scale grid. This is how calibration is carried out.

Young Technician For skilled hands 1988 No. 9

The Y (VERTICAL) channel block contains input connectors CH1 and CH2, AC/DC input switches (closed/open input), GND buttons - input grounding. The deviation coefficient is set by calibrated attenuators (VOLTS/DIV), as well as by an uncalibrated variable VAR control. The vertical offset of the oscillogram is adjusted smoothly in each channel using the POSITION knob. The oscilloscope provides the following modes of operation of the ALT/CHOP/ADD channel switch - alternate (for each sweep stroke) or intermittent channel switching (with a frequency of 250 kHz). ADD mode provides the addition of signals from channels CH1 + CH2.

Rice. 2.2. Designations of the GOS-6200 oscilloscope controls

Channel X of the oscilloscope (HORIZONTAL) contains two generators: the main one (MAIN) and the delayed sweep (DELAY). The sweep factor is set discretely (TIME/DIV). If necessary, use uncalibrated smooth adjustment with VAR mode enabled. The sweep stretch is activated by the 10 MAG button. The horizontal position of the oscillogram is adjusted with the POSITION knob. The operating mode of channel X is switched by the MAIN/ALT/DELAY button. In this case, the following operating modes of channel X are implemented:

1. MAIN sweep only.

2. Combining sweep oscillograms with highlighting the area of ​​action of the delayed sweep.

11 -

3. Only delayed sweep, launched from the main sweep with a continuously adjustable delay (DELAY TIME knob).

The scan is turned off using the X–Y mode button.

Synchronization and trigger block(TRIGGER) allows you to select the source of the synchronization signal (SOURCE), the operating mode of the scan generator (MODE) - self-oscillating (ATO), standby - NORM and triggered by a video signal (TV). The COUPLING switch is used to set the synchronization signal processing mode.

The function of the SLOPE switch is to select the polarity of the synchronization signal: (+) – synchronization on an increasing signal (triggering on an edge), (–) – on a decreasing one (triggering on a pulse cutoff). The trigger level of the synchronization and triggering device is manually adjusted using the LEVEL knob.

The oscilloscope has a trigger and trigger delay mode. Using the HO knob (combined with the DELAY TIME adjustment), you can manually increase the sweep voltage blocking time tbl. This makes it possible to increase the stability of the synchronization unit in the case when more than one trigger signal can be generated during a signal period. The normal setting for this adjustment is 0%.

The measuring unit (MEAS’MT) turns on and off the cursor measurement mode and switches the type of cursors. In normal mode, the FUNC button is used to switch functions for measuring signal parameters - frequency, period, duration and duty cycle.

The settings block (SETUPS) allows you to remember the state of the oscilloscope’s controls in memory and, if necessary, restore the previous state of the device.

Amplitude and time parameters of a standard TV video signal

In laboratory work, a standard television video signal is used as the object of study. The parameters of this signal for broadcast television systems - the period and duration of synchronization pulses, amplitude and shape - are strictly standardized in GOST 7845-92. In table 2.2 shows the standard parameters of the video signal of domestic television.

A television video signal consists of image signals, as well as horizontal and vertical blanking (blanking) and synchronizing pulses. In the video signal there are:

active interval during which the image is transmitted;

passive interval in which blanking and synchronizing pulses, color recognition signals, teletext signals, image test signals, etc. are transmitted.

	Table 2.2
Standard video parameters
Magnitude	Meaning
Number of lines
Field frequency, Hz
Line frequency, Hz
Line duration, µs
Synchronization pulse duration, μs
Duration of the front of the quenching pulse of the lines, μs
Duration of the blanking horizontal pulse, μs
Duration of a full frame, ms
Interval between the edge of the horizontal and blanking pulses, µs
Vertical blanking pulse duration (line duration)

The image signal is a voltage whose value changes continuously as the beam moves along the line in accordance with the nature of the transmission. This voltage reaches 75% of the maximum value when transmitting white and decreases to 10–15% when transmitting dark areas of the image. In Fig. Figure 2.3 shows the shape of the complete video signal of two adjacent image fields for the domestic television standard.

The amplitude values ​​of the image signal correspond to the instantaneous brightness of the transmitted image element. The zero level in the video signal is considered to be the blanking level. In the active part of the video signal (above the blanking level) there are levels of “white” (about 70% of the signal amplitude) and “black” (about 5%). The interval between the blanking level and the zero level is called the protective one. The amplitude of the sync pulse is 30% of the swing of the entire video signal.

The complete video signal contains horizontal and vertical sync pulses. They are transmitted during the reverse motion of horizontal and vertical scans, respectively. To prevent line synchronization from being disturbed during vertical scanning reverse, the vertical sync pulse has horizontal pulse inserts with a duration of 4.7 μs. With this arrangement of the transmitted sync pulses, a slight shift in the phase of the frame sync pulses of two adjacent fields is possible. This leads to a violation of the relative position of the raster lines, resulting in a deterioration in the vertical clarity of the image on the TV screen. To eliminate this phenomenon, equalizing pulses with a duration of 2.35 μs are transmitted before and after the frame pulse. The repetition rate of equalizing pulses and insertions is 2 times higher than the horizontal frequency. With them

presence, the dedicated frame sync pulses of two adjacent fields are identical
by phase and shape.
Even field					Odd field of current frame
previous frame
				Line numbers
Lowercase
	Front
equalizing					equalizing
Odd field of current frame					Even field of the current frame
				Frame damping pulse
				Line numbers
Lowercase				Personnel
sync pulse			sync pulse
			2.3. Composite Video

For video signals with a simplified sync mix without inserts and equalizing pulses (for example, signals from game consoles, simple video cameras, video testers - generators of test television signals), the vertical clarity of the image noticeably deteriorates.

Thus, on the vertical blanking pulse of a standard video signal, the synchronization signals are placed in the following order: first there are six equalizing pulses with a repetition rate of 31,250 Hz, followed by six wide pulses representing the frame synchronization signal, then again six equalizing pulses, followed by ordinary horizontal clock pulses. Due to the use of interlaced scanning, vertical scanning must be reversed 2 times during the transmission of a full frame (first after transmission of odd and then even lines). First, the beam is thrown upward after the end of the transmission of the whole line, then after the transmission of half the line. This sequence is provided by two half-frame pulses, differing from each other by various time shifts relative to the transmission of the last horizontal synchronizing pulse. In the first of them, this time corresponds to the development of one

line, and in the second - half a line. Accordingly, all other synchronizing pulses placed on the second half-frame blanking pulse are shifted by half a line. This form of signal makes it possible to obtain stable interlaced scanning, ensure the continuity of horizontal synchronizing pulses during the transmission of a vertical blanking signal, and easily separate synchronization signals from the full television signal.

The duration of pulse transmission is determined by the standard. The transmission time for one line is 64 μs. Accordingly, the transmission duration of the horizontal blanking pulse is 10...11 µs, the horizontal synchronizing pulse - 4.4...5.1 µs, the vertical blanking pulse - 1500...1600 µs, the vertical synchronizing pulse - 192 µs and, finally, the equalizing pulses - 2.56 µs. Line blanking pulses are sent after the end of each line transmission. Their value is fixed at 75% (black level) of maximum amplitude. The horizontal synchronizing pulses are placed on the horizontal blanking pulse, occupying the remaining 25% of the amplitude. They regulate the accuracy of the start of scanning of each subsequent line.

Vertical blanking pulses are sent at the end of scanning of the last line (bottom of the image). They block the beam during the return stroke as it moves from bottom to top, and serve as a “stand” for the frame sync pulses, lowering them above the signal level into the “blacker than black” region. The frame synchronizing pulse causes the beam to reverse from bottom to top in exact accordance with the movement of the beam in the transmitting tube of the television center.

The laboratory prototype consists of a GOS-6200 analog television oscilloscope, a television camera mounted on a frame along with a tablet with a test black and white image.

Assignment and instructions for performing the work

Preparing the oscilloscope for use

Before operation, study the purpose of the oscilloscope controls. Otherwise, many of the work assignments will be difficult to complete.

Check the oscilloscope calibration for the second channel CH2. To do this, use an oscilloscope probe to connect the 1:1 CAL 2V 1 kHz terminal of the oscilloscope calibrator to the input of the selected channel. Turn on the oscilloscope.

Set the CH2 channel input switch to the AC position - “closed input”, the GND button must be turned off. Select Channel Deflection Ratio

0.5 V/div, MTB MAIN = 0.5 ms/div. Let us remind you that the indication of the installed parameters and modes is carried out in the service areas of the screen. Turn on the self-oscillating scanning mode (ATO), the clock source (SOURCE) is CH2, the synchronization filter (COUPLING) is AC, the synchronization polarity SLOPE is positive. An image of a square wave (calibrator sample signal) should appear on the screen. Get a fine scan line by adjusting the brightness (INTEN) and focusing (FOCUS) of the beam.

The calibrator signal amplitude is 2 V, so with a properly calibrated Y channel, the waveform should take 4 divisions. vertically. Use the HORIZONTAL POSITION knob to align the start of the first pulse with the left vertical scale line. The coincidence of the end of the fifth period with the last right line of the scale indicates that the oscilloscope is calibrated by duration.

If the vertical and/or horizontal calibration is broken, the oscilloscope requires maintenance from a metrological service.

Measuring horizontal TV video signal parameters

Apply a video signal from a television camera to the input of channel CH1. Turn on CH1 and turn off the second channel by briefly pressing the button

Set the following control positions on the oscilloscope: channel input switch CH1 - to the DC position - “open input”,

the GND button must be disabled;

scan mode – main (MAIN);

scan start mode (MODE) - TV, sync source (SOURCE)

Using the TV-V/TV-H button, set the synchronization mode from the television video signal according to the TV-H line frequency. SLOPE synchronization polarity is negative. Select the deflection and sweep factors to display the waveforms in one or more lines on the screen. Due to the presence of vertical sync pulses in the video signal, jittery horizontal lines may appear on the screen. Sketch the appearance of the video signal of one line of the image.

Turn on the cursor measurement mode (long press the CURSOR ON/OFF button). By briefly pressing the FUNC button, select the duration measurement mode D T D. Press the CURSOR POS button and, moving the cursors with knobs C1 and C2, measure the repetition period of the horizontal sync pulses. Switch the cursors to the 1 D T D frequency measurement mode (by briefly pressing the FUNC button) and record the frequency of the horizontal pulses. Record it like this:

the same result of frequency measurement in automatic mode, which is displayed in the lower right corner of the screen. Enter the results in a table in the form of the table. 2.3.

					Table 2.3
Measured parameters of horizontal video signal
Parameter	Standard			Measured	Error,
	meaning			meaning
Period of horizontal sync pulses, μs
Horizontal pulse frequency, Hz
Horizontal pulse frequency
(automatic measurement), kHz
Duration of line quenching pulse, µs
Duration of horizontal sync pulse,
Clock shift duration
relative to the beginning of the damping pulse, μs

To measure horizontal sync pulse parameters, use delayed sweep. Set the oscilloscope to dual sweep (ALT) mode first. An image of the complete signal and a fragment of the signal created by the delayed sweep will appear on the screen (its area of ​​action is highlighted by two dotted lines - not to be confused with the cursors!). Set the delayed scan area to horizontal sync using the DELAY TIME and TIME/DIV knobs. Switch the oscilloscope to delayed sweep mode (DELAY). A large-scale image of the sync pulse will appear on the screen. Using the cursors in the D T D mode (with the CURSOR POS mode turned on), measure the duration of the blanking pulse and horizontal sync pulse, as well as the shift of the sync pulse relative to the beginning of the blanking pulse (see Fig. 2.3). Compare them with standard values. Enter the measurement results into a table in the form of the table. 2.3.

Return to the MAIN sweep mode. Measure the signal duration of the black and white fields. It looks like a step, reflecting the levels of white (maximum) and black (minimum). Turn on the voltage difference measurement cursors V 1 (FUNC button) and measure the video signal voltage levels: white level (maximum voltage value), black level (step level) and level of blanking pulses relative to the minimum voltage value - the level of horizontal sync pulses. Tabulate the results in the form of a table. 2.4. Draw the appearance of the synchronization pulse and plot the measured parameters on it.

Table 2.4

Measured parameters of the image signal of black and white fields

Duration	Duration			Amplitude	U si U max,
	steps			lowercase
Images,	white level,			impulse
		Umax, V	Umin, V
				U si, V

Measuring frame TV video signal parameters

Examine the shape of the frame sync pulse. It contains a vertical blanking pulse with a vertical sync pulse at its beginning (see Fig. 2.3). The frame sync pulse is filled with double line frequency insertion pulses. Before and after the vertical sync pulse, there are equalizing pulses of double horizontal frequency and duration, 2 times less than the duration of the horizontal sync pulses and insertion pulses.

To observe frame pulses, use the main sweep (MAIN). Use the TV-V/TV-H button to set the synchronization mode to TV-V frames. SLOPE synchronization polarity is negative. Select the main sweep factor (MTB) so as to obtain several periods of fields (half-frames) of the signal on the screen. Set the cursor measurement mode by long pressing the CURSOR ON/OFF button. Select the duration measurement mode D T D with the FUNC. button. Using cursors, measure the period and frequency of the vertical sync pulses using a method similar to that described earlier for the horizontal sync pulses. Record the result of the automatic frequency measurement displayed in the lower corner of the screen. Enter the results in a table in the form of a table.

Table 2.5

Measured frame video signal parameters

	Parameter	Standard	Measured	Error,
		meaning	meaning
	Frame sync period, ms
	Frame pulse frequency, Hz
	Vertical pulse rate
	(automatic measurement), Hz
	Frame blanking pulse duration, µs
	Frame sync pulse duration,

Turn on ALT mode and set the delayed sweep area to the second vertical blanking pulse. Switch the oscilloscope to delayed sweep mode and image the vertical blanking pulse from the start of the sync pulse to the next line image signal. Sketch its appearance.

By moving the cursors with knobs C1 and C2, measure the duration of the vertical blanking pulse and the duration of the vertical sync pulse. Compare them with standard values. Enter the measurement results into a table in the form of the table. 2.5.

Measuring the signal-to-noise ratio of a video signal from a television camera

Apply a video signal from a television camera to the input of channel CH1. Set the following control parameters on the oscilloscope: channel input switch - to the DC position - “open input”, button

GND – disable;

main scan mode – MAIN;

startup mode (MODE) – TV, clock source (SOURCE) – CH1; synchronization polarity (SLOPE) – negative;

using the TV-V/TV-H button, set the mode for selecting a given line in the system

Select the deflection and sweep factors to obtain a single line image at a convenient scale. Use the TV LINE SELECT knob to select a line within the center of the field (with a number in the range of 100–200).

Use the video camera at maximum gain by covering the lens with a light-proof cap. The camera's automatic gain control (AGC) system will set the maximum gain, and the oscillogram will show a trace of the camera's internal noise at the black signal level. Draw the resulting oscillogram of the video signal.

Place it on the top edge of the noise track (according to the largest emissions), the other on the bottom. Assuming normal noise distribution, we assume that the width of the noise track corresponds to the deviation of the random signal within 3y. Then we define y (root mean square value of noise) as

V w 6.

Measure the amplitude of the desired signal as the peak-to-peak between the signals from the black and white fields of the image. The oscillogram of such an image shows a stepped video signal. Measure its span Vc from the black level to the white level. Calculate the signal-to-noise ratio, dB, using the following formula:

Record the results of the measurement and calculation of the signal-to-noise ratio.

Lab report should contain a block diagram of the oscilloscope, measurement results, and brief conclusions.

The attachment (see picture) turns any TV into an oscilloscope with a large screen. You can observe low-frequency oscillations on it, and with the help of a sweep frequency generator (MSG) you can visually tune the IF amplifiers of radio receivers. The set-top box can be considered as a miniature television transmitter. Despite the relatively simple circuit, this transmitter produces a complete television signal, which differs from the standard one only in the absence of equalizing pulses. Frame sync pulses are generated from the reference sinusoidal voltage by the limiting amplifier VT1, the differentiating circuit R8C4 and the threshold amplifier on VT4. Their duration is about 1.9 ms. The blocking generator (on transistor VT5) generates horizontal sync pulses. These are not the main pulses of the blocking generator, but surges of the collector voltage that occur immediately after the main ones. A diode VD3 is connected between the collectors of transistors VT4 and VT5. At the moment the main pulse is generated, the collector of transistor VT4 is closed to the chassis through an open transistor VT5 and diode VD3. As a result, insets appear in the vertical sync pulses, which, as required, precede the horizontal sync pulses. The windings of the blocking generator transformer VT1 are wound on a toroidal core made of oxypherite (F-1000). The outer diameter of the core is 10 mm, thickness 2 mm. Windings I and III each contain 100 turns, and winding II contains 30 turns of PELSHO o0.1 wire. At the beginning of the horizontal scanning period, the voltage pulse of the blocking generator quickly charges capacitor C6 through the diode VD2. During the rest of the period it is slowly discharged through resistor R6. The resulting sawtooth voltage is supplied to the base of transistor VT2. Here it is added to the input voltage. The three-stage amplifier, due to its high gain (50,000-100,000), operates practically in relay mode, characterized by a certain response threshold. The attachment parameters are chosen such that in the absence of the voltage being tested, the center line is in the center of the screen. If necessary, the image on the screen can be shifted in one direction or another by changing the resistance of resistor R3. To improve the clarity of the line image on the TV screen, the amplifier (VT2, VT3, VT6) is covered by positive feedback from the collector of transistor VT3 to the base of transistor VT2 through capacitor C5. This significantly increases the gain in the high frequency region and therefore increases the slope of the output pulses. Visually, this manifests itself in an increased sharpness of the transition from white to black. Frame, line and video pulses are added at the input of the emitter repeater VT7, which is the modulation amplifier of the VHF generator VT8. The latter is assembled according to a three-point capacitive circuit. The generation frequency must be chosen equal to the carrier frequency of the image of a free television channel. Otherwise, the set-top box may interfere with the operation of neighboring TVs. The required generation frequencies can be obtained by selecting the number of turns of coil L1.

When tuning to the second television channel (59.25 MHz), coil L1 contains 5 turns of PEV 0.6 wire, coil diameter 9 mm. The modulated RF voltage is supplied to the output of the set-top box through a divider R18-R19, which reduces the voltage to 3 mV to avoid overloading the RF path of the TV. The output of the set-top box is connected with a coaxial cable or twisted double wire to the antenna input of the TV.

Construction and setup. All parts of the set-top box, with the exception of the VHF generator, can be placed on the circuit board in any order. Parts related to the VHF generator (SP-S15, L1, VT8) must have short leads, they should be connected to each other using short conductors and grouped in one place. No shielding of the set-top box is required. If the pulse frequency of the block generator does not lie in the line frequency range of the TV, it is necessary to enter it into this range by changing the resistance of resistor R14 within small limits. It should be noted that the synchronization of TV scans from the set-top box is usually very stable, so poor synchronization when setting up the set-top box indicates some kind of installation error. To achieve precise tuning of the VHF generator of the set-top box to the selected television channel, you have to stretch or compress the turns of the winding of the L1 coil, i.e. change the winding pitch. When set correctly, the line on the screen is sharply defined. The parameters of the set-top box are selected so that the largest image size on the TV screen corresponds to an input voltage of about 0.3 V. The sensitivity of the set-top box can be adjusted by changing the resistance of resistor R2. To test sensitivity, an alternating voltage of a known magnitude or from a sound generator is supplied to the input.

RADUAMATOR 6/99, Shronin, Kremenchug, Poltava region.