DEGREES OF COMPARISON OF ADJECTIVES In English, as in Russian, ...
For digital control of voltage and current in the power supply, it is not necessary to manufacture the ADC and indicator yourself. For this purpose, a Chinese multimeter worth $ 3-4 is quite suitable, which is comparable in price to the cost of manufacturing your own digital indication.
The popular M830B was chosen for the rework. Below in detail, in the pictures, the alteration of the multimeter is described to indicate the voltage and current in your power supply.
The main point of the alteration was to reduce the size of the board with the indicator, i.e. I just had to cut off part of the board. For rework, the simplest and cheapest Chinese multimeter M830B was purchased. The M830B multimeter circuit can be downloaded from our file archive. The voltage measurement limit of our design will be 200 V, and the current limit will be 10 A. To select the measurement mode "Voltage" - "Current", switch S1 with two groups of contacts is used. The diagram shows the position of the switch in voltage measurement mode.
First you need to disassemble the multimeter and pull out the board. You can see the view of the board from the side of the details in the photo.
And here is a photo of the board from the side of the indicator.
Our design will be placed on two boards. One board with an indicator, another board with details of the input part of the multimeter and an additional 9 volt stabilizer. The diagram of the second board is shown in the picture. Soldered resistors from the multimeter board are used as divider resistors. Their designation on the diagram corresponds to the designations on the M830B multimeter board. The diagram also provides additional explanations. Letters in circles correspond to the connection points of one board to another. To power the structure, a low-power voltage stabilizer is used, which is connected to a separate winding of the transformer.
Let's actually get started. We solder R18, R9, R6, R5. We save resistors R6 and R5 for the input part of our design. We cut off the upper contact R10 from the circuit and cut out part of the track (marked with crosses in the photo). Solder R10. Solder R12 and R11.
R12 and R11 are connected in series. And solder one end to the upper contact R10, and the other to the track cut off from R10. Solder R20 and solder it in place of R9. Solder R16 and drill new holes for it (see photo)
Solder R16 to a new location.
And here is a view of R16 soldering from the side of the indicator.
We take scissors for metal and cut off part of the board.
We turn the board over with the indicator towards us. The contact R9 closest to the indicator (now there is R20) is cut off from the circuit (marked with a cross). We connect the contacts R9 farthest from the indicator (now there is R20) and R19 together (from the side of the indicator), in the photo it is indicated by a red jumper. The upper contact R10 (there are now R11 and R12) is connected to the lower contact R13, indicated by a red jumper in the photo. Delete part of the tracks marked with crosses. And solder the jumper to the contact R9 closest to the indicator (now there is R20), instead of the remote track.
We remove the tracks marked with a cross, and prepare the contact patches for desoldering with the second board, indicated by arrows in the photo.
Solder the jumper. We solder the contact wires from the second board, observing the correspondence of the letters (a-A, b-B, etc.)
All! The design is assembled, we proceed to the test. We connect to a power source and measure the voltage of the battery. Works!
In this photo, the design is built into the power supply, for which it was created. When the load is connected, by pressing the "Voltage-Current" button, the value of the flowing current is displayed on the indicator.
Do-it-yourselfers are offered a simple tester based on the M2027-M1 microammeter, which has a measurement range of 0-300 μA, an internal resistance of 3000 ohms, and an accuracy class of 1.0.
Required Parts
This is a tester that has a magnetoelectric mechanism for measuring current, so it only measures direct current. The movable coil with an arrow is attached to the braces. It is used in analog electrical measuring instruments.
Finding it at a flea market or buying it in a radio parts store will not be a problem. There you can also purchase other materials and components, as well as attachments to the multimeter. In addition to a microammeter, you will need:
If a person decides to make himself a multimeter with his own hands, then he does not have other measuring instruments. Based on this, we will continue to act.
Selection of measurement ranges and calculation of resistor values
Let's determine the range of measured voltages for the tester. Let's choose the three most common ones that cover most of the needs of a radio amateur and a home electrician. These ranges are 0 to 3V, 0 to 30V, and 0 to 300V.
The maximum current passing through a homemade multimeter is 300 µA. Therefore, the task is reduced to the selection of additional resistance, at which the arrow will deviate to full scale, and a voltage corresponding to the limit value of the range will be applied to the series circuit Rd + Rvn.
That is, in the range of 3 V, Rtotal \u003d Rd + Rin \u003d U / I \u003d 3 / 0.0003 \u003d 10000 Ohm,
where Rtotal is the total resistance, Rd is the additional resistance, and Rin is the internal resistance of the tester.
Rd \u003d Rtotal-Rin \u003d 10000-3000 \u003d 7000 Ohm or 7kOhm.
On the 30 V range, the total resistance should be 30 / 0.0003 \u003d 100000 Ohm
Rd \u003d 100000-3000 \u003d 97000 Ohm or 97 kOhm.
For 300 V range Rtot=300/0.0003=1000000 Ohm or 1 mOhm.
Rd \u003d 1000000-3000 \u003d 997000 Ohm or 997 kOhm.
To measure currents, we select the ranges from 0 to 300 mA, from 0 to 30 mA and from 0 to 3 mA. In this mode, the shunt resistance Rsh is connected to the microammeter in parallel. That's why
Rtotal = Rsh * Rin / (Rsh + Rin).
And the voltage drop across the shunt is equal to the voltage drop across the tester coil and is equal to Upr=Ush=0.0003*3000=0.9 V.
From here, in the range of 0 ... 3 mA
Rtotal=U/I=0.9/0.003=300 Ohm.
Then
Rsh \u003d Rtotal * Rin / (Rin-Rtotal) \u003d 300 * 3000 / (3000-300) \u003d 333 Ohm.
In the range of 0…30 mA Rtot=U/I=0.9/0.030=30 Ohm.
Then
Rsh \u003d Rtotal * Rin / (Rin-Rtotal) \u003d 30 * 3000 / (3000-30) \u003d 30.3 Ohm.
Hence, in the range of 0…300 mA Rtotal=U/I=0.9/0.300=3 Ohm.
Then
Rsh \u003d Rtotal * Rin / (Rin-Rtotal) \u003d 3 * 3000 / (3000-3) \u003d 3.003 Ohm.
Fitting and mounting
To make the tester accurate, you need to adjust the resistor values. This part of the work is the most painstaking. Prepare the board for mounting. To do this, you need to draw it into squares measuring a centimeter by a centimeter or a little less.
Then, with a shoe knife or something similar, the copper coating is cut along the lines to the fiberglass base. We got isolated contact pads. We noted where the elements would be located, it turned out like a wiring diagram right on the board. In the future, tester elements will be soldered to them.
In order for a home-made tester to give the correct readings with a given error, all its components must have the same accuracy characteristics, at least, and even higher.
The internal resistance of the coil in the magnetoelectric mechanism of the microammeter will be considered equal to 3000 Ohm declared in the passport. The number of turns in the coil, the diameter of the wire, the electrical conductivity of the metal from which the wire is made are known. So, the manufacturer's data can be trusted.
But the voltages of 1.5 V batteries may differ slightly from those declared by the manufacturer, and knowledge of the exact voltage value will then be required to measure the resistance of resistors, cables and other loads with a tester.
Determining the exact battery voltage
In order to find out the actual voltage of the battery yourself, you will need at least one accurate resistor with a nominal value of 2 or 2.2 kOhm with an error of 0.5%. This resistor value was chosen due to the fact that when a microammeter is connected in series with it, the total resistance of the circuit will be 5000 ohms. Therefore, the current passing through the tester will be about 300 µA, and the needle will deviate to full scale.
I=U/R=1.5/(3000+2000)=0.0003 A.
If the tester shows, for example, 290 µA, then the battery voltage is
U=I*R=0.00029(3000+2000)=1.45 V.
Now, knowing the exact voltage on the batteries, having one exact resistance and a microammeter, you can select the necessary resistance values of the shunts and additional resistors.
Collecting the power supply
The power supply for the multimeter is assembled from two 1.5 V batteries connected in series. After that, a microammeter and a 7 kOhm resistor pre-selected at face value are connected to it in series.
The tester should show a value close to the current limit. If the device goes off scale, then in series with the first resistor it is necessary to connect a second, small value.
If the readings are less than 300 μA, then in parallel to these two resistors, a large resistance is connected. This will reduce the total resistance of the additional resistor.
Such operations continue until the needle is set to the scale limit of 300 µA, which indicates a fine fit.
To select the exact 97 kOhm resistor, we select the closest one that is suitable at face value, and follow the same procedures as with the first 7 kOhm resistor. But since a 30 V power supply is needed here, it will be necessary to remake the multimeter's power supply from 1.5 V batteries.
A block is assembled with an output voltage of 15-30 V, as long as it lasts. For example, it turned out to be 15 V, then the entire adjustment is made on the basis that the arrow should tend to a reading of 150 μA, that is, to half the scale.
This is acceptable, since the scale of the tester when measuring current and voltage is linear, but it is desirable to work with full voltage.
To adjust the additional resistor of 997 kOhm for the 300 V range, you will need DC or voltage generators. They can also be used as attachments to the multimeter when measuring resistance.
Resistor ratings: R1=3 ohm, R2=30.3 ohm, R3=333 ohm, R4 variable at 4.7 kOhm, R5=7 kOhm, R6=97 kOhm, R7=997 kOhm. Chosen by fit. Power supply 3 V. Installation can be done by hanging elements directly on the board.
The connector can be installed on the side wall of the box into which the microammeter crashes. The probes are made of single-core copper wire, and the cords to them are made of multi-core.
The shunts are connected by a jumper. As a result, a tester is obtained from a microammeter, which can measure all three main parameters of electric current.
A miniature Chinese voltmeter can simplify the process of measuring voltage and the amount of current consumed on a power supply or homemade charger. Its cost rarely exceeds 200 rubles, and if you order it from China through affiliate programs, you can also get a tangible discount.
To charger
Those who like to design chargers on their own will appreciate the opportunity to observe the volts and amperes of the network, without the help of bulky portable devices. It will also appeal to those who work on expensive equipment, the operation of which can be adversely affected by a regular drop in mains voltage.
With the help of a Chinese ammeter, which is no larger than a matchbox, you can easily monitor the state of the electrical network. One of the tangible problems that beginner electricians have is the language barrier and wire markings that differ from the standard. Not everyone will immediately understand which wire to connect where, and instructions are usually only in Chinese.
100 V / 10 A devices are very popular with independent designers. It is also desirable that the device has a shunt to refine the connection process. A notable advantage of this device is that it can be connected to the power supply of the charger or to an independent battery.
* The voltage of the power supply of the ammeter, voltmeter should be in the range from 4.5 to 30 V.
The connection diagram is as follows:
- The black wire is negative. It must also be connected to negative.
- The red wire, which should be thicker than the black one, is a plus and must be connected to the power supply accordingly.
- The blue wire connects the load to the network.
If everything was connected correctly, two scales should be highlighted on the display.
To power supply
Power supplies play an important role, align the network readings to the desired state. If not operated correctly, they can severely damage expensive equipment by causing overheating. In order to avoid problems during their operation, and especially in cases where the power supply is made by hand, it is advisable to use an inexpensive ammeter, voltmeter.
A variety of models can be ordered from China, but for standard devices powered by a home network, those that measure current from zero to 20 A and voltage up to 220 V are suitable. Almost all of them are small and can be installed in small power supply cases.
Most devices can be adjusted using built-in resistors. In addition, they have high accuracy, almost 99%. The display shows six positions, three for voltage and current. They can be powered both from a separate and from a built-in source.
To connect a voltmeter, you need to deal with the wires, there are five of them:
- Three thin ones. Black minus, red plus, yellow to measure the difference.
- Two fat ones. Red plus, black minus.
The first three cords are most often combined for convenience. The connection can be made through a special female connector, or by soldering.
*Soldering connection is more reliable, with slight vibrations, the socket mount of the device may become loose.
Step by step connection:
- It is necessary to decide from which power source the device will operate, separate or built-in.
- Black wires are connected and soldered to the minus of the PSU. Thus, a general negative is created.
- In the same way, you need to connect the thin red and yellow contacts. They are connected to the power supply.
- The remaining red contact will connect to the electrical load.
If the connection is incorrect, the instrument panel will show zero values. In order for the measurements to be as close as possible to the real ones, it is necessary to correctly observe the polarity of the supply contacts. Only connecting a thick red wire to the load will give an acceptable result.
Note! You can only get accurate voltage values on a regulated power source. In other cases, the display will show only the voltage drop.
A popular voltmeter model that is often used by radio amateurs. It has the following characteristics:
- Operating voltage DC 4.5 to 30 V.
- Power consumption less than 20 mA.
- Dual color red and blue display. Resolution 0.28 inches.
- Performs measurements in the range 0 - 100 V, 0 - 10 A.
- Lower limit 0.1 V and 0.01 A.
- Error 1%.
- Temperature conditions of work from -15 to 75 degrees Celsius.
Connection
Using a voltmeter, you can measure the current voltage in the power supply network. To do this, you need the following:
- Connect the black thick wire to the minus of the power source.
- Red connects to the load, and then to power.
This wiring diagram does not provide for the use of a thin black contact.
If a third-party power supply is used, then the connection will be as follows:
- Thick cords are connected in the same way as in the previous example.
- Thin red is connected to the plus of a third-party source.
- Black with minus.
- Yellow with source plus.
This voltmeter, ammeter is also convenient because it is implemented in an already calibrated state. But even if inaccuracies were noticed in its operation, they can be corrected using two tuning resistors on the back of the device.
What are the most reliable digital voltmeters
The electrical equipment market is crowded with manufacturers who provide a wide variety of choices. However, not every device brings positive emotions from use. For a large number of goods, it is not always possible to find a reliable and inexpensive copy.
Proven and reliable voltmeters include:
- TK 1382. Inexpensive Chinese, the average price of which rarely rises above 300 rubles. Equipped with tuning resistors. Carries out measurements in the ranges of 0-100 Volts, 0-10 Amps.
- YB27VA. Practically a twin of the previous voltmeter, it is distinguished by wire marking and a reduced price.
- BY42A. It costs more than previous models, but also has an increased upper limit of measurements of 200 V.
These are the most popular representatives of this type of voltmeters, which can be freely purchased for conversion on the radio market or ordered via the Internet.
Chinese Voltmeter Ammeter Calibration
Over time, any technology wears out. Since the operation of measuring instruments is affected not only by their own malfunctions, but also by failures in the connected devices, sometimes you need to do some adjustment.
Most models have special resistors on their case. By rotating them, you can change the zero values.
All measuring instruments have a measurement error, which is indicated in the documentation.
Conclusion
The inclusion of inexpensive voltmeters in the circuit avoids problems with inappropriate mains voltage. For a small fee, you can find out if the equipment works in suitable conditions. To connect them, you need to know the marking of all wires and the location of the plus and minus of the energy source.
Each owner of the Chinese multimeter DT830 and similar models must have encountered some inconveniences during operation that are not visible at first glance.
For example, the constant discharge of the battery due to the fact that they forgot to put the switch in the off position. Or the lack of backlight, impractical wires and much more.
All this can be easily modified and the functionality of your cheap multimeter can be upgraded to the level of individual professional foreign models. Let's consider in order what is missing and what can be added to the work of any multimeter without any special capital costs.
Replacing the wire and probes of the multimeter
First of all, what 99% of users of cheap Chinese multimeters face is the failure of low-quality measurement probes.
First, the tips of the probes can break. When touching an oxidized or slightly rusty surface for measurement, this surface must be lightly sanded to make good contact. The most convenient way to do this, of course, is with the probe itself. But as soon as you start scratching, at this moment the tip may break off.
Secondly, the cross section of the wires included in the kit also does not stand up to criticism. Not only are they flimsy, but this will also affect the error of the multimeter. Especially when the resistance of the probes themselves during measurements plays a significant role.
Most often, a wire break occurs at the connection points on the plug-in contact and directly on the soldering of the sharp tip of the probe. 
When this happens, you will be surprised how thin the wires inside are really. 
Meanwhile, the multimeter must be designed to measure current loads up to 10A! How this can be done with such a wire is not clear. 
Here is the actual current consumption measurement data for flashlights, made using standard probes included in the kit and using homemade probes with a cross section of 1.5mm2. The difference in error, as you can see, is more than significant. 
The plug-in contacts in the multimeter connectors also become loose over time and worsen the overall resistance of the circuit during measurements.
In general, the unequivocal verdict of all owners of DT830 multimeters and other models is that the probes must be modified or changed immediately after purchasing the tool. 
If you are a happy owner of a lathe or you have a familiar turner, then the handles of the probes can be made independently from some kind of insulating material, such as pieces of unnecessary plastic.
The tips of the probes are made from a sharpened drill. The drill itself is a hardened metal and you can safely scrape off any soot or rust without risk of damaging the probe. 
When replacing plug-in contacts, it is best to use these plugs used in audio equipment for speaker jacks. 
If you are completely collective farming or there are no other options at hand, then in extreme cases you can use ordinary contacts from a collapsible plug.
They also fit perfectly under the connector on the multimeter. 
At the same time, do not forget to insulate with a thermotube the ends that will stick out outside the multimeter, in the places where the wires are soldered to the plug.
When there is no possibility to make probes on your own, then the case can be left the same, replacing only the wires.
In this case, three options are possible:
After replacement, such wires will be very easy to assemble into a bundle and not get confused.
Secondly, they are designed for a huge number of bends and will break no sooner than the multimeter itself fails.
Thirdly, the measurement error due to their larger cross section compared to the original ones will be minimal. That is, there are positives everywhere.
If you make long wires up to 1.5 m, taking into account all the connections, the resistance on them can reach several ohms!An important note: when replacing wires, you should not strive to make them much longer than those that came with the kit. Remember that the length of the wire, as well as its cross section, affects the total resistance of the circuit.
Those who do not want to do homemade products can order ready-made high-quality silicone probes with many tips on Aliexpress. 
To make new probes with wire occupy a minimum of space, you can twist them in a spiral. To do this, a new wire is wound on a tube, wrapped with electrical tape for fixation, and the whole thing is heated with a building hair dryer for a couple of minutes. As a result, you get this result. 
In a cheap version, such a focus will not work. And when using a building hair dryer to warm up, the insulation can float at all.
Refinement of the multimeter mount
Another inconvenience when measuring with a multimeter is the lack of a third hand. You constantly have to hold the multimeter in one hand, and work with two probes at the same time with the other. 
If the measurements take place at the desktop, then there is no problem. Put down the tool, free your hands and work. 
But what if you measure the voltage in the shield or in the junction box under the ceiling?
The problem is solved simply and inexpensively. In order to be able to fix the multimeter on a metal surface, on the back of the device with hot melt adhesive or double-sided tape, glue ordinary flat magnets. 
And your device will be no different from expensive foreign analogues. 
Another option for an inexpensive upgrade of the multimeter in terms of its convenient placement and installation on the surface during measurements is the manufacture of a home-made stand. To do this, you only need 2 paper clips and hot melt adhesive. 
And if you do not have any surface at all nearby where you can place the tool, what to do in this case? Then you can use an ordinary wide elastic band, for example from suspenders. 
You make a ring out of gum, pass it through the body and that's it. Thus, the multimeter can be conveniently fixed directly on the arm, like a watch.
Firstly, now the multimeter will never fall out of your hands again, and secondly, the readings will always be in front of your eyes. 
Caps for probes
The spikes at the ends of the probes are sharp enough that you can prick painfully. Some models come with protective caps, some do not. 
They also get lost quite often. But in addition to the danger of pricking a finger, they also protect the contacts from breaking when the multimeter is in a bag interspersed with another tool.
In order not to buy spare parts every time, you can make them yourself. Take an ordinary cap from a helium pen and lubricate the probe tip with any oil. This is done so that the cap does not stick to the surface during the manufacturing process.
Then fill the inner surface of the cap with hot glue and put it on the sharp tip. 
Wait until the hot glue hardens and calmly remove the resulting result. 
Multimeter backlight
The function that the multimeter lacks in poorly lit places is the backlight of the display. Solving this problem is not difficult, just apply:
Make a hole in the side of the case for the switch. Glue the reflector under the indication display and solder two wires to the crown contacts. 
From them, power is supplied to the switch and then to the LEDs. The structure is ready.
In the end result, a home-made refinement of the backlight of the multimeter will look like this: 
The backlit battery will drain much faster, so be sure to turn off the switch when there is enough natural light.
Replacing the crown in the multimeter with a lithium-ion battery from the phone
In recent years, it has become very popular to remake a multimeter to replace the power supply from the original crown with a lithium-ion battery from cell phones and smartphones. For these purposes, in addition to the battery itself, you will need charge-discharge boards. They are bought on Aliexpress or other online stores. 
The overdischarge protection board for such batteries is initially built into the battery in its upper part. It is necessary so that the battery is not discharged above the nominally permissible norms (about 3 volts and below). 
The charging board does not allow you to recharge the battery over 4.2 volts (link to aliexpress). 
In addition, you will need a board that increases the voltage from 4V to the required 9V (link to aliexpress). 
The battery itself is compactly placed on the back cover and does not interfere with its closing at all. 
First, on the step-up module, you must set the output voltage to 9 volts. Connect it with wires to a multimeter that has not yet been converted and unscrew the required value with a screwdriver. 
You will have to make a hole in the case for a micro or mini usb charging connector.
The step-up module itself is located in the place where the crown should be. 
Be sure to make sure that the wiring from the module to the battery is of the required length. In the future, this will allow you to remove the cover without any problems, and, having split the case in half, if necessary, deal with the internal revision of the multimeter.
After placing all the parts inside, it remains to solder the wiring according to the diagram and fill everything with hot glue so that nothing moves when the device is moved. 
It is desirable to fill with hot glue not only the case, but also contacts with wires in order to extend their service life. 
A significant drawback of such a multimeter on a lithium-ion battery is its operation, or rather, not operation at low temperatures.
It is worth your multimeter to lie down in the trunk of a car or in a bag in the winter for a long time, and you will immediately remember the battery krone.
And think about it, was such an alteration useful? Ultimately, of course, you decide, based on the operating conditions of the device.
Refinement of the on and off button on the multimeter
It is advisable to improve the last version of the multimeter refinement with the transition to lithium-ion batteries even more by placing the shutdown button in the power supply circuit of the converter to the battery. 
Firstly, the converter itself draws a small amount of current, even in standby mode when the multimeter is not working.
Secondly, thanks to this switch, you don’t have to click the multimeter itself once again to turn it off. Many devices fail prematurely because of this reason.
Some tracks are erased ahead of time, others begin to shorten among themselves. So the button to turn off the entire device at once will be very handy.
Another tip from experienced users of Chinese multimeters is that in order for the switch to last a long time and work properly, immediately after purchase, disassemble and lubricate the sliding points of the switch balls. 
And on the board it is recommended to smear the tracks with technical vaseline. Since new devices do not have lubrication and the switch wears out quickly. 
You can make a button both in the internal design, if you find free space, and in the external one. To do this, you will have to drill only two micro holes for the power wiring. 
Flashlight in multimeter
Another innovation for the multimeter is the optional flashlight option. Often you have to use the device to look for damage in the switchboards and switch cabinets of basements, wiring short circuits in rooms where there is no light.
An ordinary white LED and a button specifically for turning it on are added to the circuit. It is very easy to check how much luminous flux from a given LED is enough. You don't even have to take it apart to do it.
Place the anode leg of the diode in connector E, and the cathode leg in connector C (the anode leg is longer than the cathode). All this is done in the connectors for the transistor measurement mode on the P-N-P block. 
The LED will glow in any position of the switch and will go out only when you turn off the multimeter yourself. To mount all this inside, you need to find the necessary conclusions on the circuit board and solder two wires to the emitter (connector E) and collector (connector C). A button is soldered into the wire break and mounted through a hole in the multimeter case. 
Secure everything with hot glue and get a portable multimeter flashlight.
I received a couple of electronic built-in voltmeters from AliExpress model V20D-2P-1.1 (measurement of direct voltage), the issue price is 91 cents a piece. In principle, you can now find it cheaper (if you search well), but it’s not a fact that this will not be at the expense of the build quality of the device. Here are its characteristics:
- operating range 2.5 V - 30 V
- glow color red
- overall size 23 * 15 * 10 mm
- does not require additional power (two-wire version)
- it is possible to adjust
- update rate: about 500ms/time
- promised measurement accuracy: 1% (+/-1 digit)
And everything would be fine, I put it in place and used it, but I came across information about the possibility of their refinement - adding a current measurement function.
Digital Chinese Voltmeter I prepared everything you need: a bipolar toggle switch, output resistors - one MLT-1 for 130 kOhm and the second wire for 0.08 Ohm (made from a nichrome spiral with a diameter of 0.7 mm). And for the whole evening, according to the scheme found and the manual for its implementation, he connected this economy with wires to a voltmeter. To no avail. Either there was not enough ingenuity in understanding the unsaid and underdrawn in the found material, or there were differences in the schemes. The voltmeter didn't work at all.
We connect the digital voltmeter module I had to solder the indicator and study the circuit. Here it was already required not a small soldering iron, but a tiddly one, so that it tinkered fairly. But over the next five minutes, when the whole scheme became available for review, I understood everything. In principle, I knew that I should start with this, but I really wanted to solve the issue “easily”.
V-meter refinement scheme
Refinement scheme: ammeter to voltmeter So this scheme was born for connecting additional electronic components with those already existing in the voltmeter circuit. The standard circuit resistor marked in blue must be removed. I will say right away that I found differences from other circuits given on the Internet, for example, the connection of a tuning resistor. I didn’t redraw the entire voltmeter circuit (I’m not going to repeat it), I drew only the part that is necessary for refinement. I consider it obvious that the power supply of the voltmeter should be done separately, after all, the starting point in the readings should start from zero. Later it turned out that power from a battery or accumulator would not work, because the current consumption of a voltmeter at a voltage of 5 volts is 30 mA.
Board - Chinese voltmeter module After assembling the voltmeter, he took up the essence of the action. I won’t be wise, I’ll just show and tell you what to combine with what to make it work.
Step-by-step instruction
So, act one- an SMD resistor with a resistance of 130 kOhm is soldered from the circuit, standing at the input of the positive power wire, between the diode and the trimming resistor of 20 kOhm.
We connect the resistor to the voltmeter-ammeter Second. On the released contact, a wire of the desired length is soldered from the side of the trimmer (it is convenient for the sample to be 150 mm and preferably red)
Solder SMD resistor Third. On the track connecting the 12 kΩ resistor and the capacitor, a second wire (for example, blue) is soldered from the "ground" side.
Testing a new circuit
Now, according to the diagram and this photo, we “hang” an addition on the voltmeter: a toggle switch, a fuse and two resistors. The main thing here is to properly solder the newly installed red and blue wires, however, not only them.
We convert the block voltmeter into an A-meter And here there are more wires, although everything is simple:
» - an electric motor is connected with a pair of connecting wires« separate power supply for the voltmeter"- battery with two more wires
« power supply output"- a couple more wires
After power was supplied to the voltmeter, “0.01” immediately appeared, after power was supplied to the electric motor, the meter in voltmeter mode showed a voltage at the output of the power supply equal to 7 volts, then switched to ammeter mode. Switching was performed when the power supply to the load was turned off. In the future, instead of a toggle switch, I will put a button without fixation, it is safer for the circuit and more convenient for operation. I was pleased that everything worked on the first try. However, the readings of the ammeter were different from the readings on the multimeter by more than 7 times.
Chinese voltmeter - ammeter after alteration Here it turned out that the wire resistor instead of the recommended resistance of 0.08 ohms has 0.8 ohms. I made a mistake in the measurement during its manufacture in counting zeros. I got out of the situation like this: a crocodile with a negative wire from the load (both black) moved along a straightened nichrome spiral towards the input from the power supply, the moment when the readings of the multimeter and the now modified ampervoltmeter coincided and became the moment of truth. The resistance of the involved section of the nichrome wire was 0.21 Ohm (measured with a prefix to the multimeter at the limit of "2 Ohm"). So it didn’t even turn out badly that instead of 0.08, the resistor turned out to be 0.8 ohms. No matter how you count, according to the formulas, you still have to adjust. For clarity, the result of his efforts was recorded on a video.
Video
I consider the acquisition of these voltmeters successful, but it’s a pity that their current price in that store has grown a lot, almost $ 3 apiece. Written by Babay from Barnaula.
