Recently I already reviewed one construction kit, today is a continuation of a small series of reviews about all sorts of homemade things for beginner radio amateurs.
I’ll say right away that this is certainly not Tectronics, or even DS203, but it’s an interesting thing in its own way, even though it’s essentially a toy.
Usually, before testing, the thing is first disassembled, here you have to assemble it first :)
In my opinion, these are the “eyes” of a radio amateur. This device rarely has high accuracy, unlike a multimeter, but it allows you to see processes in dynamics, i.e. in move".
Sometimes such a second “look” can help more than a day of fiddling with the tester.
Previously, oscilloscopes were tube oscilloscopes, then they were replaced by transistor ones, but the result was still displayed on the CRT screen. Over time, they were replaced by their digital counterparts, small, light, and the logical continuation was the appearance of a designer for assembling such a device.
Several years ago, on some forums, I came across attempts (sometimes successful) to develop a homemade oscilloscope. The designer is of course simpler than them and weaker in technical characteristics, but I can say with confidence that even a schoolchild can assemble it.
This construction set was developed by jyetech. of this device on the manufacturer's website.
Perhaps this review will seem overly detailed to specialists, but the practice of communicating with novice radio amateurs has shown that they perceive information better this way.
In general, I’ll tell you about everything a little below, but for now the standard introduction, unpacking.
They sent the construction set in a regular zip-lock bag, although quite thick.
In my opinion, such a set would really benefit from some nice packaging. Not for the purpose of protection from damage, but for the purpose of external aesthetics. After all, the thing should be pleasant even at the unpacking stage, because it is a construction set. 
The package contained:
Instructions
Printed circuit board
Cable for connecting to measured circuits
Two bags of ingredients
Display. 
The technical characteristics of the device are very modest, as for me it is more of a training set than a measuring device, although even with the help of this device it is possible to carry out measurements, albeit simple ones. 
The kit also includes detailed color instructions on two sheets.
The instructions describe the sequence of assembly, calibration and a brief guide to use.
The only negative is that it’s all in English, but the pictures are made clearly, so even in this version most of it will be understandable.
The instructions even indicate the positional positions of the elements and make “checkboxes” where you need to put a tick after completing a certain stage. Very thoughtful. 
There is a separate sheet of paper with a list of SMD components.
It is worth noting that there are at least two variants of the device. On the first, only the microcontroller is initially soldered, on the second, all SMD components are soldered.
The first option is designed for slightly more experienced users.
This is the option that is included in my review; I learned about the existence of the second option later. 
The printed circuit board is double-sided, as in the previous review, even the color is the same.
On top there is a mask with the designation of the elements, one part of the elements is fully designated, the second has only a position number according to the diagram. 
There are no markings on the reverse side, there is only a designation of jumpers and the name of the device model.
The board is covered with a mask, and the mask is very durable (I had to check it involuntarily), in my opinion, what is needed specifically for beginners, since it is difficult to damage anything during the assembly process. 
As I wrote above, the designations of the installed elements are marked on the board, the markings are clear, there are no complaints about this item. 
All contacts are tinning, the board is soldered very easily, well, almost easily, more on this nuance in the assembly section :) 
As I wrote above, a microcontroller is preinstalled on the board
This is a 32-bit microcontroller based on the ARM 32-bit Cortex™-M3 core.
The maximum operating frequency is 72 MHz, and it also has 2 x 12-bit, 1 μs ADC. 
On both sides of the board its model is indicated, DSO138. 
Let's return to the list of components.
Small radio components, connectors, etc. Packed in small snap bags. 
Pour the contents of a large bag onto the table. Inside there are connectors, stands and electrolytic capacitors. Also in the package there are two more small bags :) 
Having opened all the packages, we see quite a lot of radio components. Although, given that this is a digital oscilloscope, I expected more.
It’s nice that the SMD resistors are labeled, although in my opinion, it wouldn’t hurt to label regular resistors as well, or provide a small color-coding guide in the kit. 
The display is packed in soft material; as it turned out, it does not slip, so it will not dangle in the bag, and the printed circuit board protects it from damage during transportation.
But still, I think that normal packaging would not hurt. 
The device uses a 2.4-inch TFT LCD indicator with LED backlight.
Screen resolution 320x240 pixels. 
A small cable is also included. To connect to the oscilloscope, a standard BNC connector is used; at the other end of the cable there is a pair of alligator clips.
The cable is medium soft, the crocodiles are quite large. 
Well, here’s a view of the entire set completely unfolded. 
Now you can move on to the actual assembly of this constructor, and at the same time try to figure out how difficult it is.
Last time I started the assembly with resistors, as the lowest elements on the board.
If you have SMD components, it is better to start assembly with them.
To do this, I laid out all the SMD components on the attached sheet, indicating their nominal value and position designation on the diagram. 
When I was ready to solder, I thought that the elements were in a case that was too small for a beginner, it would be quite possible to use resistors of size 1206 instead of 0805. The difference in the space taken up is insignificant, but soldering is easier.
The second thought was - now I’ll lose the resistor and won’t find it. Okay, I’ll open the table and take out a second such resistor, but not everyone has such a choice. In this case, the manufacturer took care of this.
I gave all the resistors (it’s a pity that they weren’t microcircuits) by one more, i.e. in reserve, very prudently, offset. 
Next I’ll talk a little about how I solder such components, and how I advise others to do it, but this is just my opinion, of course, everyone can do it in their own way.
Sometimes SMD components are soldered using a special paste, but it is not often that a beginning radio amateur (and even a non-beginner) has it, so I will show you how easier it is to work without it.
We take the component with tweezers and apply it to the installation site. 
In general, I often first coat the installation site of the component with flux; this makes soldering easier, but complicates cleaning the board; it can sometimes be difficult to wash the flux out from under the component.
Therefore, in this case I simply used 1mm tubular solder with flux.
Holding the component with tweezers, place a drop of solder on the soldering iron tip and solder one side of the component.
It’s okay if the soldering turns out ugly or not very strong; at this stage it’s enough that the component holds itself together.
Then we repeat the operation with the remaining components.
After we have secured all the components in this way (or all components of the same denomination), we can safely solder them as needed; to do this, we turn the board so that the already soldered side is on the left and hold the soldering iron in your right hand (if you are right-handed), and the solder in with the left, we go through all the unsoldered places. If the soldering of the second side is not satisfactory, then rotate the board 180 degrees and similarly solder the other side of the component.
This makes it easier and faster than soldering each component individually. 
Here in the photo you can see several installed resistors, but so far soldered only on one side. 
Microcircuits in an SMD package are marked in the same way as in a regular one, on the left near the mark (although usually on the bottom left when looking at the marking) there is the first contact, the rest are counted counterclockwise.
The photo shows the location for installing the microcircuit and an example of how it should be installed. 
We proceed with microcircuits in a completely similar way to the example with resistors.
We place the microcircuit on the pads, solder any one pin (preferably the outermost one), slightly adjust the position of the microcircuit (if necessary) and solder the remaining contacts.
You can do different things with the stabilizer microcircuit, but I advise you to solder the petal first, and then the contact pads, then the microcircuit will definitely lie flat on the board.
But no one forbids soldering the outermost pin first, and then all the others. 
All SMD components are installed and soldered, there are a few resistors left, one of each value, put them in a bag, maybe they will come in handy someday. 
Let's move on to installing conventional resistors.
In the last review I talked a little about color coding. This time I would rather advise you to simply measure the resistance of the resistors using a multimeter.
The fact is that the resistors are very small, and with such sizes the color marking is very difficult to read (the smaller the area of the painted area, the more difficult it is to determine the color).
Initially, I looked for a list of denominations and positional designations in the instructions, but I couldn’t find them, because I was looking for them in the form of a plate, and after installation it turned out that they were in the pictures, with checkboxes for marking the established positions.
Because of my carelessness, I had to make my own plate, on which I laid out the installed components next to each other.
On the left you can see the resistor separately; when compiling the plate it was superfluous, so I left it at the end. 
We proceed with resistors in a similar way as in the previous review; we shape the terminals using tweezers (or a special mandrel) so that the resistor easily falls into place.
Be careful, the positional designations of components on the board can be not only labeled, but also SIGNED, and this can play a cruel joke on you, especially if there are many components in one row on the board. 
This is where a small minus of the printed circuit board came out.
The fact is that the holes for the resistors have a very large diameter, and since the installation is relatively tight, I decided to bend the leads, but not too much, and therefore they do not hold very well in such holes. 
Due to the fact that the resistors did not hold up very well, I recommend not filling in all the values at once, but installing half or a third, then soldering them and installing the rest.
Don’t be afraid to bite the pins too much, a double-sided board with metallization forgives such things, you can always solder a resistor even on top, which you can’t do with a single-sided printed circuit board. 
That's it, the resistors are sealed, let's move on to the capacitors.
I treated them the same way as resistors, laying them out according to the plate.
By the way, I still have one extra resistor left, apparently they put it in by accident. 
A few words about labeling.
Such capacitors are marked in the same way as resistors.
The first two digits are the number, the third digit is the number of zeros after the number.
The resulting result is equal to the capacitance in picofarads.
But there are capacitors on this board that do not fall under this marking; these are values of 1, 3 and 22pF.
They are marked simply by indicating the capacitance since the capacitance is less than 100pF, i.e. less than three digits. 
First, I solder the small capacitors according to the positional designations (that’s a quest). 
With capacitors with a capacity of 100 nF, I stepped a little, without adding them to the plate right away, I had to do it later by hand. 
I also did not bend the leads of the capacitors completely, but at about 45 degrees, this is quite enough to prevent the component from falling out.
By the way, in this photo you can see that the spots connected to the common contact of the board are made correctly, there is an annular gap to reduce heat transfer, this makes it easier to solder such places. 
Somehow I relaxed a little on this board and remembered about the chokes and diodes after soldering the ceramic capacitors, although it would have been better to solder them in front of them.
But this didn’t really change the situation, so let’s move on to them.
The board was supplied with three chokes and two diodes (1N4007 and 1N5815). 
Everything is clear with the diodes, the location is labeled, the cathode is marked with a white stripe on the diode itself and on the board, it is very difficult to confuse.
With chokes it can be a little more complicated, they are sometimes also color coded, fortunately in this case all three chokes have the same rating :) 
On the board, the chokes are indicated by the letter L and a wavy line.
The photo shows a section of the board with sealed chokes and diodes. 
The oscilloscope uses two transistors of different conductivity and two stabilizer microcircuits with different polarities. In this regard, be careful when installing, since the designation 78L05 is very similar to 79L05, but if you put it the other way around, you will most likely go for new ones.
With transistors it is a little simpler, although the board simply shows the conductivity without indicating the type of transistor, but the type of transistor and its position designation can be easily seen from the diagram or component installation map.
The terminals here are noticeably more difficult to mold, since all three terminals need to be molded; it is better not to rush, so as not to break off the terminals. 
The conclusions are formed in the same way, this simplifies the task.
The position of the transistors and stabilizers is indicated on the board, but just in case, I took a photo of how they should be installed. 
The kit included a powerful (relatively) inductor, which is used in the converter to obtain negative polarity, and a quartz resonator.
They don’t need to draw conclusions. 
Now about the quartz resonator, it is made for a frequency of 8 MHz, it also has no polarity, but it is better to put a piece of tape under it, since its body is metal and it lies on the tracks. The board was covered with a protective mask, but I’m somehow used to making some kind of backing in such cases, for safety.
Don’t be surprised that at the beginning I indicated that the processor has a maximum frequency of 72 MHz, and the quartz costs only 8, inside the processor there are both frequency dividers and sometimes multipliers, so the core can easily operate, for example, at a frequency of 8x8 = 64 MHz.
For some reason, the inductor contacts on the board are square and round in shape, although the inductor itself is a non-polar element, so we simply solder it in place; it is better not to bend the leads. 
The kit included quite a few electrolytic capacitors, they all have the same capacitance of 100 μF and a voltage of 16 Volts.
They must be soldered with correct polarity, otherwise pyrotechnic effects are possible :)
The long lead of the capacitor is the positive contact. The board has polarity markings both near the corresponding pin and next to the circle marking the position of the capacitor, which is quite convenient.
The positive output is marked. Sometimes they mark it as negative, in which case approximately half of the circle is shaded. And then there is a computer hardware manufacturer like Asus, which shades the positive side, so you always have to be careful. 
Little by little we came to a rather rare component, the trimmer capacitor.
This is a capacitor whose capacitance can be changed within small limits, for example 10-30pF, usually the capacitance of these capacitors is small, up to 40-50pF.
In general, this is a non-polar element, i.e. Formally, it doesn’t matter how you solder it, but sometimes it matters how you solder it.
The capacitor contains a screwdriver slot (like the head of a small screw) that has an electrical connection to one of the terminals. SO in this circuit, one terminal of the capacitor is connected to the common conductor of the board, and the second to the remaining elements.
To reduce the influence of the screwdriver on the circuit parameters, it is necessary to solder it so that the pin connected to the slot is connected to the common wire of the board.
The board is marked on how to solder it, and later in the review there will be a photo where you can see this. 
Buttons and switches.
Well, it’s hard to do something wrong here, since it’s very difficult to insert them somehow :)
I can only say that the terminals of the switch body must be soldered to the board.
In the case of a switch, this will not only add strength, but will also connect the switch body to the common contact of the board and the switch body will act as a shield from interference. 
Connectors.
The most difficult part in terms of soldering. It is difficult not because of the accuracy or small size of the component, but on the contrary, sometimes it is difficult to warm up the soldering area, so for the BNC connector it is better to take a more powerful soldering iron. 
In the photo you can see -
Soldering a BNC connector, an additional power connector (the only connector here that can be installed in reverse) and a USB connector. 
There was a slight problem with the indicator, or rather with the connectors for connecting it.
The kit forgot to include a pair of double contacts (pins), they are used here to secure the side of the indicator opposite the signal connector. 
But after looking at the pinout of the signal connector, I realized that some contacts could easily be bitten off and used instead of the missing ones.
I could open the desk drawer and take out such a connector from there, but it would be uninteresting and to some extent dishonest. 
We solder the socket (so-called female) parts of the connectors onto the board. 
The board has an output of a built-in 1KHz generator, we will need it later, although these two contacts are connected to each other, we still solder in a jumper, it will be convenient for connecting the “crocodile” signal cable.
For the jumper it is convenient to use the bitten lead of an electrolytic capacitor; they are long and quite rigid.
This jumper is located to the left of the power connector. 
There are also a couple of important jumpers on the board.
One of them, called JP3 it must be short-circuited immediately, this is done with a drop of solder. 
With the second jumper, it’s a little more complicated.
First you need to connect the multimeter in voltage measurement mode at the test point located above the petal of the stabilizer chip. The second probe is connected to any contact connected to the common contact of the board, for example to a USB connector.
Power is supplied to the board and the voltage at the test point is checked, if everything is in order, then there should be about 3.3 Volts. 
After this jumper JP4, located slightly to the left and below the stabilizer, is also connected using a drop of solder. 
There are four more jumpers on the back of the board; you don’t need to touch them; these are technological jumpers for diagnosing the board and switching the processor to firmware mode. 
Let's return to the display. As I wrote above, I had to bite off several contact pairs in order to use them to replace the missing ones.
But when assembling, I decided not to bite out the outer pairs, but from the middle, as it were, and solder the outer one in place, so it would be more difficult to confuse something during installation. 
Although there is a protective film on the display, I would recommend covering the screen with a piece of paper when soldering the connector, in which case drops of flux that boils during soldering will fly off onto the paper and not onto the screen. 
That's it, you can apply power and check :)
By the way, one of the diodes that we soldered earlier serves to protect the electronics from incorrect power connections; on the part of the developer, this is a useful step, since the board can be burned with the wrong polarity in a second.
The board indicates a power supply of 9 Volts, but a range of up to 12 Volts is specified.
In the tests, I powered the board from a 12 Volt power supply, but I also tried from two series-connected lithium batteries, the difference was only in a slightly lower brightness of the screen backlight, I think that by using a 5 Volt stabilizer with a low drop and removing the protective diode (or connecting it in parallel with the power supply and installing a fuse), you can easily power the board from two lithium batteries.
Alternatively, use a 3.7-5 Volt power converter. 
Since the startup of the board was successful, it is better to wash the board before setting it up.
I use acetone, although it is prohibited for sale, but there are small reserves; as an option, we also used toluene, or, in extreme cases, medical alcohol.
But the board must be washed, you don’t need to “bathe” it entirely, just go over it from below with a cotton swab. 
At the end, we put the board “on its feet” using the supplied stands; of course, they are a little smaller than necessary and dangle a little, but it’s still more convenient than just putting it on the table, not to mention the fact that the pins of the parts can scratch the table top, and so on. this way nothing gets under the board and shorts out anything underneath it. 
The first test is from the built-in generator, for this we connect the crocodile with a red insulator to the jumper near the power connector; there is no need to connect the black wire anywhere. 
I almost forgot, a few words about the purpose of switches and buttons.
On the left are three three-position switches.
The top one switches the input operating mode.
Grounded
Operating mode without taking into account the constant component, or AC, or operating mode with a closed input. Well suited for AC current measurements.
Operating mode with the ability to measure direct current, or operating mode with an open input. Allows measurements taking into account the constant voltage component.
The second and third switches allow you to select the scale along the voltage axis.
If 1 Volt is selected, this means that in this mode a swing of one scale cell of the screen will be equal to a voltage of 1 Volt.
At the same time, the middle switch allows you to select the voltage, and the lower multiplier, therefore, using three switches, you can select nine fixed voltage levels from 10 mV to 5 Volts per cell.
On the right are buttons for controlling scan modes and operating modes.
Description of the buttons from top to bottom.
1. When pressed briefly, it turns on the HOLD mode, i.e. recording readings on the display. when long (more than 3 seconds), turns on or off the mode of digital output of signal parameter data, frequency, period, voltage.
2. Button to increase the selected parameter
3. Button to decrease the selected parameter.
4. Button to cycle through operating modes.
Sweep time control, range from 10 µs to 500 sec.
Select the operating mode of the synchronization trigger, Auto, normal and standby.
The mode of capturing the synchronization signal by a trigger, at the front or rear of the signal.
Selecting the voltage level of the synchronization trigger signal capture.
Scrolling the waveform horizontally allows you to view the signal “off the screen”
Setting the vertical position of the oscillogram helps when measuring signal voltages and when the oscillogram does not fit on the screen...
The reset button, simply rebooting the oscilloscope, as it turned out, is sometimes very convenient.
There is a green LED next to the button; it blinks when the oscilloscope has synchronized.
All modes when the device is turned off are remembered and it then turns on in the mode in which it was turned off.
There is also a USB connector on the board, but as I understand it, it is not used in this version; when connected to a computer, it displays that an unknown device has been detected.
There are also contacts for flashing the device.
All modes selected by buttons or switches are duplicated on the oscilloscope screen. 
I did not update the software version, since it is the latest one at the moment 113-13801-042 
Setting up the device is very simple; the built-in generator helps with this.
Most likely, when you connect to the built-in rectangular pulse generator, you will see the following picture; instead of even rectangles, there will be either a “collapse” of the top/bottom angle, down or up. 
This is corrected by rotating the tuning capacitors.
There are two capacitors, in the 0.1 Volt mode we adjust C4, in the 1 Volt mode, respectively, C6. In 10mV mode no adjustment is made. 
By adjusting it is necessary to achieve even rectangular pulses on the screen, as shown in the photograph. 
I looked at this signal with another oscilloscope, in my opinion it is “smooth” enough to calibrate this oscilloscope. 
Although the capacitors are installed correctly, even in this option there is a slight influence from the metal screwdriver, as long as we hold the tip on the adjustable element, the result is the same, as soon as you remove the tip, the result changes slightly.
In this option, either tighten it with small shifts, or use a plastic (dielectric) screwdriver.
I got such a screwdriver with some kind of Hikvision camera. 
On one side it has a cross tip, cut off, specifically for such capacitors, on the other it is straight. 
Since this oscilloscope is more a device for studying the principles of operation than a truly full-fledged device, I don’t see the point in conducting full testing, although I will show and check the main things.
1. I completely forgot, sometimes when working, a manufacturer’s advertisement appears at the bottom of the screen :)
2. Displays the digital values of the signal parameter, a signal is supplied from the built-in rectangular pulse generator.
3. This is the intrinsic noise of the oscilloscope input; I have seen mentions of this on the Internet, as well as the fact that the new version has a lower noise level.
4. To check that this is really noise from the analog part and not interference, I switched the oscilloscope to the mode with a short-circuited input. 
1. Switched the sweep time to 500 seconds per division mode, as for me, well, this is really for extreme sports enthusiasts.
2. The input signal level can be changed from 10mV per cell
3. Up to 5 Volts per cell.
4. Rectangular signal with a frequency of 10 KHz from the generator of the DS203 oscilloscope. 
1. Rectangular signal with a frequency of 50 KHz from the generator of the DS203 oscilloscope. It can be seen that at this frequency the signal is already highly distorted. 100KHz doesn't make much sense anymore.
2. Sinusoidal signal with a frequency of 20 KHz from the generator of the DS203 oscilloscope.
3. Triangular signal with a frequency of 20 KHz from the generator of the DS203 oscilloscope.
4. Ramp signal with a frequency of 20 KHz from the generator of the DS203 oscilloscope. 
Next, I decided to look a little at how the device behaves when working with a sinusoidal signal supplied from an analog generator and compare it with my DS203
1. Frequency 1KHz
2. Frequency 10KHz 
1. Frequency 100KHz, in the designer you cannot select a sweep time less than 10ms, that’s why it’s the only way :(
2. And this is what a sinusoidal signal with a frequency of 20KHz, fed from the DS203, may look like, but in a different input divider mode. Above was a screenshot of such a signal, but given in the position of the divider 1 Volt x 1, here the signal is in the 0.1 Volt x 5 mode.
Below you can see what this signal looks like when fed to the DS203 
20KHz signal supplied from an analog generator. 
Comparative photo of two oscilloscopes, DSO138 and DS203. Both are connected to an analog sine generator, frequency 20KHz, both oscilloscopes are set to the same operating mode. 
Summary.
pros
Interesting educational design
High-quality printed circuit board, durable protective coating.
Even a novice radio amateur can assemble the set.
Well-thought-out packaging, I was pleased with the spare resistors included.
The instructions describe the assembly process well.
Minuses
Low frequency input signal.
They forgot to include a couple of contacts for attaching the indicator.
Simple packaging.
My opinion. Let me say briefly, if I had such a construction set in my childhood, I would probably be very happy, even despite its shortcomings.
Long story short, I was pleasantly surprised by the designer; I consider it a good base both in gaining experience in assembling and setting up an electronic device, and in working with a very important device for a radio amateur - an oscilloscope. It may be simple, even without memory and with a low frequency, but it is much better than fiddling with audio cards.
Of course, it cannot be considered a serious device, but it is not positioned as such, but as a designer, more than anything.
Why did I order this designer? Yes, it was just interesting, because we all love toys :)
I hope that the review was interesting and useful, I’m looking forward to suggestions regarding testing options :)
Well, as always, additional materials, firmware, instructions, sources, diagram, description -
Homemade oscilloscopes are no longer a rarity as microcontrollers develop. And naturally the need for a probe for it arises. Preferably with a built-in divider. Some of the possible designs are discussed in this article.
The probe is assembled on a piece of foil fiberglass and placed in a metal tube that acts as a screen. In order not to cause emergency situations when and if the probe falls on the switched-on device under test, the tube is covered with heat shrink. Without coating, the workpiece looks like this:
Disassembled probe:
Designs may vary. Just need to consider some things:
In my case, the connection of the tube to the screen (more precisely, to the back side of the fiberglass laminate) is made by soldering a spring onto the tectolite, which creates contact between the screen and the probe board.
As a needle I used a “Dad” from a ShR type connector. But it can be made from any other suitable rod. The connector from the ShR is convenient in that its “Mother” can be soldered into a clamp, which can be put on the probe if necessary.
The selection of wire deserves special mention. The correct wire looks like this:
The 3.5 mm minijack is located nearby for scale
The correct wire is a more or less ordinary shielded wire, with one significant difference - it has one central core. Very thin and made of steel wire, or even wire with high resistivity. I’ll explain why a little later.
This type of wire is not very common and is quite difficult to find. In principle, if you do not work with high frequencies of the order of ten megahertz, you may not feel much of a difference using a regular shielded wire. I have come across the opinion that at frequencies below 3-5 MHz the choice of wire is not critical. I can neither confirm nor deny - there is no practice at frequencies above 1 MHz. I will also tell you later in what cases this may have an effect.
Homemade oscilloscopes don't often have multi-megahertz bandwidth, so use whatever wire you can find. Just try to choose one with thinner central cores and fewer of them. I have come across the opinion that the central core should be thicker, but this is clearly part of the series of “bad advice”. Low resistance to the oscilloscope wire is unnecessary. There currents are in nanoamperes.
And it is important to understand that the lower the intrinsic capacity of the manufactured probe, the better. This is due to the fact that when you connect the probe to the device under test, you are thereby connecting additional capacitance.
If you connect directly to the output of a logical element or to a UPS, i.e. to a sufficiently powerful signal source that has a sufficiently low intrinsic resistance, then everything will be displayed normally. But if there is significant resistance in the circuit, then the probe capacitance will greatly distort the signal shape, because will charge through this resistance. This means that you will no longer be sure of the reliability of the oscillogram. Those. The lower the probe's intrinsic capacitance, the wider the range of possible uses for your oscilloscope.
Actually, the probe circuit that I used is extremely simple:
This is a divider by 10 for an oscilloscope with a 1 meg input impedance. It is better to make up several resistors connected in series. The switch simply closes the additional resistance directly. A tuning capacitor allows you to match the probe with a specific device.
Perhaps here is a more correct scheme that would be worth recommending:
It is clearly better in terms of permissible voltage, since the breakdown voltage of SMD resistors and capacitors is usually taken as 100 volts. I've come across claims that they can withstand 200-250 volts. Didn't check. But if you are examining fairly high-voltage circuits, you should use just such a circuit.
Capacitance is directly proportional to the area of the conductors and inversely proportional to the distance between them. There is still a coefficient there, but for us it is not important now.
We have two conductors. Central core and wire screen. The distance between them is determined by the diameter of the wire. It is not possible to reduce the screen area much. No need to. It remains to reduce the SURFACE AREA OF THE CENTRAL VEIN.
Those. reduce its diameter as far as technically feasible without loss of mechanical strength.
Well, in order to increase this same strength while reducing the diameter, you need to choose a stronger material.
The wire can be represented like this:
Distributed capacitance along the length of the wire. Well, the greater the resistivity of the material of the central core, the less influence neighboring areas (adjacent containers) will have on each other. Therefore, a wire with high resistivity is advisable. For the same reason, it is not advisable to make the probe wire too long.
I won't look at the connectors. I’ll just say that I think BNC connectors are optimal for an oscilloscope. They are most often used. I would not recommend using a minijack or audio jack (although I use it myself, due to the fact that I do not use an oscilloscope in circuits with significant voltages). He's dangerous. The wire was pulled while testing circuits with good voltage. What happens next? And then the minijack, sliding along the socket, can cause a short circuit. And even if, for various reasons, nothing happened, this voltage will be present on the minijack itself. What if he falls into your lap? And there is an open central contact and ground nearby...
Additional information can be gleaned from a series of articles. So, we got tired of the theory, now
The good thing about it is that it can be inserted like this:
Or like this, he doesn’t care, he spins freely.
It's structured something like this:
The only thing that will still be done on it. The hole for the ground wire to exit from the probe will be filled with a drop of hot-melt adhesive to make it more difficult to pull it out during an accidental tug, and the wire will be fixed in the handle with a piece of a match sharpened to a flat wedge.
So as not to break or unscrew the central core. By the way, this is the easiest way to “treat” cheap Chinese tester probes so that the wire does not break off from the tip.
What you should pay attention to: The screen extends almost to the tip. There should not be a significant open area of the central core under your fingers, otherwise you will admire the hand guidance on the donkey’s display.
Especially for the Radioschemes website - Trishin A.O. Komsomolsk-on-Amur. August 2018
Discuss the article HOMEMADE PROBE FOR AN OSCILLOSCOPE
It is difficult for any radio amateur to imagine his laboratory without such an important measuring instrument as an oscilloscope. And, indeed, without a special tool that allows you to analyze and measure the signals acting in the circuit, repairing most modern electronic devices is impossible.
On the other hand, the cost of these devices often exceeds the budgetary capabilities of the average consumer, which forces him to look for alternative options or make an oscilloscope with his own hands.
You can avoid purchasing expensive electronic products in the following cases:
Each of the options listed above, which allow you to make an oscilloscope with your own hands, is not always applicable. To fully work with self-assembled attachments and modules, the following prerequisites must be met:
Thus, an oscilloscope from a sound card, in particular, does not allow measuring oscillatory processes with frequencies outside its operating range (20 Hz-20 kHz). And to make a USB set-top box for a PC, you will need some experience in assembling and configuring complex electronic devices (as when connecting to a regular tablet).
Note! The option in which it is possible to make an oscilloscope from a laptop or tablet using the simplest approach comes down to the first case, which involves the use of a built-in circuit breaker.
Let's look at how each of the above methods is implemented in practice.
To implement this method of obtaining an image, you will need to make a small-sized attachment, consisting of only a few electronic components accessible to everyone. Its diagram can be found in the picture below.
The main purpose of such an electronic chain is to ensure the safe entry of the external signal under study to the input of the built-in sound card, which has its “own” analog-to-digital converter (ADC). The semiconductor diodes used in it guarantee that the signal amplitude is limited to a level of no more than 2 Volts, and a divider made of resistors connected in series allows voltages with large amplitude values to be supplied to the input.
A wire with a 3.5 mm plug at the mating end is soldered to the board with resistors and diodes on the output side, which is inserted into the circuit breaker socket called “Linear input”. The signal under study is supplied to the input terminals.
Important! The length of the connecting cord should be as short as possible to ensure minimal signal distortion at very low measured levels. It is recommended to use a two-core wire in a copper braid (screen) as such a connector.
Although the frequencies passed by such a limiter are in the low-frequency range, this precaution helps to improve the quality of transmission.
In addition to the technical equipment, before starting measurements, you should prepare the appropriate software. This means that you need to install on your PC one of the utilities designed specifically for obtaining an oscillogram image.
Thus, in just an hour or a little more it is possible to create conditions for research and analysis of electrical signals using a stationary PC (laptop).
In order to adapt a regular tablet for recording oscillograms, you can use the previously described method of connecting to an audio interface. In this case, certain difficulties are possible, since the tablet does not have a discrete line input for a microphone.
This problem can be solved as follows:
The advantages of this method of connecting to a computer are ease of implementation and low cost. Its disadvantages include the small range of measured frequencies, as well as the lack of a 100% guarantee of safety for the tablet.
These shortcomings can be overcome through the use of special electronic set-top boxes connected via a Bluetooth module or via a Wi-Fi channel.
Connection via Bluetooth is carried out using a separate gadget, which is a set-top box with an ADC microcontroller built into it. By using an independent information processing channel, it is possible to expand the bandwidth of the transmitted frequencies to 1 MHz; in this case, the input signal value can reach 10 Volts.
Additional Information. The range of action of such a self-made attachment can reach 10 meters.
However, not everyone is able to assemble such a converter device at home, which significantly limits the range of users. For anyone who is not ready to manufacture a set-top box on their own, there is an option to purchase a finished product, which has been available for free sale since 2010.
The above characteristics may suit a home mechanic who repairs not very complex low-frequency equipment. For more labor-intensive repair operations, professional converters with a bandwidth of up to 100 MHz may be required. These capabilities can be provided by a Wi-Fi channel, since the speed of the data exchange protocol in this case is incomparably higher than in Bluetooth.
The option of transmitting digital data using this protocol significantly expands the throughput of the measuring device. Set-top boxes that work on this principle and are freely sold are not inferior in their characteristics to some examples of classical oscilloscopes. However, their cost is also far from being considered acceptable for users with average incomes.
In conclusion, we note that taking into account the above limitations, the Wi-Fi connection option is also suitable only for a limited number of users. For those who decide to abandon this method, we advise you to try to assemble a digital oscilloscope that provides the same characteristics, but by connecting to a USB input.
This option is also very difficult to implement, so for those who are not completely confident in their abilities, it would be wiser to purchase a ready-made USB set-top box that is commercially available.
An oscilloscope is a tool that almost every radio amateur has. But for beginners it is too expensive.
The problem of high cost is easily solved: there are many options for making an oscilloscope.
The computer is perfect for such a modification, and its functionality and appearance will not be affected in any way.
The circuit diagram of an oscilloscope is difficult for a novice radio amateur to understand, so it should not be considered as a whole, but first broken down into separate blocks:
Each block represents a separate microcircuit or board.
The signal from the device under test is supplied through the Y input to the input divider, which sets the sensitivity of the measuring circuit. After passing through the pre-amplifier and delay line, it reaches the final amplifier, which controls the vertical deflection of the indicator beam. The higher the signal level, the more the beam is deflected. This is how the vertical deflection channel is designed.
The second channel is horizontal deflection, needed to synchronize the beam with the signal. It allows you to keep the beam in the place specified by the settings.
Without synchronization, the beam will float off the screen.
There are three types of synchronization: from an external source, from the network and from the signal being studied. If the signal has a constant frequency, then it is better to use synchronization from it. The external source is usually a laboratory signal generator. Instead, a smartphone with a special application installed on it is suitable for these purposes, which modulates the pulse signal and outputs it to the headphone jack.
Oscilloscopes are used in the repair, design and configuration of various electronic devices. This includes car system diagnostics, troubleshooting in household appliances and much more.
The oscilloscope measures:
It also allows you to sweep a signal down to thousandths of a second and view it in great detail.
Most oscilloscopes have a built-in frequency counter.
There are many options for making homemade USB oscilloscopes, but not all of them are accessible to beginners. The simplest option would be to assemble it from ready-made components. They are sold in radio stores. A cheaper option would be to buy these radio components in Chinese online stores, but you need to remember that components purchased in China may arrive in a faulty condition, and money for them is not always returned. After assembly, you should get a small set-top box that connects to a PC.
This version of the oscilloscope has the highest accuracy. If the problem arises of which oscilloscope to choose for repairing laptops and other complex equipment, it is better to opt for it.
For production you will need:
You need to collect according to this scheme:
Usually, radio amateurs use the etching method to make printed circuit boards. But you won’t be able to make a double-sided printed circuit board with complex layout in this way yourself, so you need to order it in advance from a factory that produces such boards.
To do this, you need to send a drawing of the board to the factory, according to which it will be manufactured. The same factory makes boards of different quality. It depends on the options selected when placing your order.
In order to get a good payment in the end, you need to indicate in the order the following conditions:
After receiving the finished board and purchasing all the radio components, you can begin assembling the oscilloscope.
The first to assemble is a DC-DC converter that produces voltages of +5 and -5 volts.
It needs to be assembled on a separate board and connected to the main one. using shielded cable.
Solder the microcircuits to the main board carefully, without overheating them. The temperature of the soldering iron should not be higher than three hundred degrees, otherwise the soldered parts will fail.
After installing all the components, assemble the device into a suitable-sized case and connect it to the computer with a USB cable. Close jumper JP1.
You need to install and launch the Cypress Suite program on your PC, go to the EZ Console tab and click on LG EEPROM. In the window that appears, select the firmware file and press Enter. Wait for the message Done to appear, indicating the successful completion of the process. If the message Error appears instead, it means that an error occurred at some stage. You need to restart the flasher and try again.
After flashing the firmware, your self-made digital oscilloscope will be completely ready for use.
At home, radio amateurs usually use stationary devices. But sometimes a situation arises when you need to repair something located far from home. In this case, you will need a portable, self-powered oscilloscope.
Before starting assembly, prepare the following components:
You need to disassemble the wireless headset and remove the control board from it. Unsolder the microphone, power button and battery from it. Set the board aside.
Instead of Bluetooth headphones, you can use a Bluetooth audio module.
Use a knife to scrape off the remaining sponge from the box and clean it well using detergents. Wait until it dries and cut out holes for the button, switch and connectors.
Solder the wires to the sockets, holder, button and switch. Place them in place and secure with hot glue.
The wires must be connected as follows shown in the diagram:
Explanation of symbols:
Then download the virtual oscilloscope application from the play market and install it on your smartphone. Turn on the Bluetooth module and synchronize it with your smartphone. Connect the probes to the oscilloscope and open its software on your phone.
When you touch the signal source with the probes, a curve showing the signal level will appear on the screen of your Android device. If it doesn't appear, it means a mistake was made somewhere.
You should check the correct connection and serviceability of the internal components. If everything is ok, you need to try to start the oscilloscope again.
This version of a homemade oscilloscope is easily installed in the housing of a desktop LCD monitor. This solution allows you to save some space on your desktop.
For assembly you will need:
Every radio amateur can build an oscilloscope into a monitor with his own hands. First you need to remove the back cover from the monitor and find a place to install the motherboard. Once you have decided on the location, next to it you need to cut holes in the case for the button and USB connector.
The second end of the cable must be soldered to the board from the tablet. Before soldering each wire, test it with a multimeter. This will help you avoid confusing the order in which they are connected.
Next step You need to remove the power button and micro USB connector from the tablet board. Solder wires to the clock button and USB socket and secure them in the cut holes.
Then connect all the wires as shown in the figure and solder them:
Place a jumper between the GND and ID contacts in the micro USB connector. This is necessary to switch the USB port to OTG mode.
You need to glue the inverter and the motherboard from the tablet with double-sided tape, and then snap the monitor cover.
Connect the mouse to the USB port and press the power button. While the device is booting up, turn on the Bluetooth transmitter. Then you need synchronize it with the receiver. You can open the oscilloscope application and verify the functionality of the assembled device.
Instead of a monitor, an old LCD TV that does not have a Smart TV is also perfect. The tablet's hardware surpasses many Smart TV systems in its capabilities. You should not limit its use to just an oscilloscope.
An oscilloscope assembled from an external audio adapter will cost only 1.5-2 dollars and will take a minimum of time to manufacture. In size it will be no larger than a regular flash drive, and in terms of functionality it will not be inferior to its larger brother.
Required parts:
You need to disassemble the audio adapter; to do this, you need to pry the housing halves open and separate them.
Remove capacitor C6 and solder a resistor in its place. Then install the board back into the case and reassemble it.
You should cut off the standard plug from the probes and solder a mini-jack in its place. Connect the probes to the audio input of the audio adapter.
Then you need to download the corresponding archive and unpack it. Insert the card into the USB connector.
The simplest thing left is to go to Device Manager and in the “Audio, game and video devices” tab, find the connected USB audio adapter. Right-click on it and select “Update Driver”.
Then move the files miniscope.exe, miniscope.ini and miniscope.log from the archive to a separate folder. Run "miniscope.exe".
Before use, the program must be configured. The necessary settings are shown in the screenshots:
If you touch the signal source with the probes, a curve should appear in the oscilloscope window:
So to turn audio adapter for oscilloscope, you need to put in a minimum of effort. But it is worth remembering that the error of such an oscilloscope is 1-3%, which is clearly not enough to work with complex electronics. It is perfect for a beginner radio amateur, but craftsmen and engineers should take a closer look at other, more accurate oscilloscopes.
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. https://site/
The article also talks about how you can measure input and output impedance and how to calculate an attenuator for a virtual oscilloscope.
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. https://site/
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.
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.
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.
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.
You can skip this paragraph. It is designed for lovers of small details.
The output impedance (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).
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.
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 (once)
This means that the total division ratio in the switch position 1:20 should be:
21,14*20 = 422,8 (once)
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 (once)
We calculate the resistor value for the divider.
1007*50 / (50*2114 –50 –1007) ≈ 0,481 (kOhm)
To make calculations easier, check out this link:
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.
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.
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.
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.
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 is “zero” skin is written.
In my opinion, this is the fastest and easiest way, which, nevertheless, gives very good results.
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.
