Figure 1 shows a circuit of a digital ammeter and voltmeter, which can be used as an addition to circuits of power supplies, converters, chargers, etc. The digital part of the circuit is implemented on a PIC16F873A microcontroller. The program provides voltage measurement 0... 50 V, measured current - 0... 5 A.
LED indicators with a common cathode are used to display information. One of the operational amplifiers of the LM358 chip is used as a voltage follower and serves to protect the controller in emergency situations. Still, the price of the controller is not so low. The current is measured indirectly, using a current-voltage converter made by the operational amplifier DA1.2 of the LM358 microcircuit and the transistor VT1 - KT515V. You can also read about such a converter. The current sensor in this circuit is resistor R3. The advantage of this current measurement circuit is that there is no need for precise adjustment of the milliohm resistor. You can simply adjust the ammeter readings with trimmer R1 and within a fairly wide range. The load current signal for further digitization is removed from the load resistor of the converter R2. The voltage on the filter capacitor located after the rectifier of your power supply unit (stabilizer input, point 3 on the diagram) should not be more than 32 volts, this is due to the maximum supply voltage of the op-amp. The maximum input voltage of the KR142EN12A microcircuit stabilizer is thirty-seven volts.
Adjusting the voltammeter is as follows. After all the procedures - assembly, programming, checking for compliance, the product you have assembled is supplied with supply voltage. Resistor R8 sets the voltage at the output of the KR142EN12A stabilizer to 5.12 V. After this, the programmed microcontroller is inserted into the socket. Measure the voltage at point 2 with a multimeter that you trust, and use resistor R7 to achieve the same readings. After this, a load with a control ammeter is connected to the output (point 2). In this case, equal readings of both devices are achieved using resistor R1.
You can make a current sensor resistor yourself, using, for example, steel wire. To calculate the parameters of this resistor, you can use the program “Did you download the program?” Have you opened it? So, we need a resistor with a nominal value of 0.05 Ohm. To make it, we will choose steel wire with a diameter of 0.7 mm - this is what I have, and it does not rust. Using the program, we calculate the required length of the segment having such resistance. Let's look at the screenshot of this program's window. 
And so we need a piece of stainless steel wire with a diameter of 0.7 mm and a length of only 11 centimeters. There is no need to twist this segment into a spiral and concentrate all the heat at one point. Look like that's it. What is not clear, please go to the forum. Good luck. K.V.Yu. I almost forgot about the files.
When working with various electronic products, there is a need to measure the modes or distribution of alternating voltages on individual circuit elements. Conventional multimeters turned on in AC mode can only record large values of this parameter with a high degree of error. If you need to take small readings, it is advisable to have an AC millivoltmeter that allows you to take measurements with an accuracy of millivolts.
In order to make a digital voltmeter with your own hands, you need some experience working with electronic components, as well as the ability to handle an electric soldering iron well. Only in this case can you be sure of the success of assembly operations carried out independently at home.
Microprocessor based voltmeter
Parts selection
Before making a voltmeter, experts recommend carefully studying all the options offered in various sources. The main requirement for such selection is the extreme simplicity of the circuit and the ability to measure alternating voltages with an accuracy of 0.1 Volt.
An analysis of many circuit solutions has shown that for self-manufacturing a digital voltmeter, it is most advisable to use a programmable microprocessor of the PIC16F676 type. For those who are new to the technique of reprogramming these chips, it is advisable to purchase a chip with ready-made firmware for a homemade voltmeter.
When purchasing parts, special attention should be paid to choosing a suitable indicator element on LED segments (the option of a standard pointer ammeter in this case is completely excluded). In this case, preference should be given to a device with a common cathode, since the number of circuit components in this case is noticeably reduced.
Additional Information. Conventional purchased radioelements (resistors, diodes and capacitors) can be used as discrete components.
After purchasing all the necessary parts, you should proceed to wiring the voltmeter circuit (making its printed circuit board).
Preparing the board
Before making a printed circuit board, you need to carefully study the circuit of the electronic meter, taking into account all the components present on it and placing them in a place convenient for desoldering.
Important! If you have available funds, you can order the production of such a board in a specialized workshop. The quality of its execution in this case will undoubtedly be higher.
After the board is ready, you need to “stuff” it, that is, place all the electronic components (including the microprocessor) in their places, and then solder them with low-temperature solder. Refractory compounds are not suitable in this situation, since they will require high temperatures to heat them up. Since all the elements in the assembled device are miniature, their overheating is extremely undesirable.
Power supply (PSU)
In order for the future voltmeter to function normally, it will need a separate or built-in DC power supply. This module is assembled according to the classical scheme and is designed for an output voltage of 5 Volts. As for the current component of this device, which determines its calculated power, half an ampere is quite enough to power the voltmeter.
Based on these data, we prepare ourselves (or send it to a specialized workshop for manufacturing) a printed circuit board for the power supply.
Note! It would be more rational to prepare both boards at once (for the voltmeter itself and for the power supply), without spacing these procedures out over time.
When manufactured independently, this will allow you to perform several similar operations at once, namely:
- Cutting blanks of the required size from fiberglass sheets and cleaning them;
- Making a photomask for each of them with its subsequent application;
- Etching these boards in a ferric chloride solution;
- Stuffing them with radio components;
- Soldering of all placed components.
In the case when boards are sent for manufacturing on proprietary equipment, their simultaneous preparation will also allow you to benefit both in price and in time.
Assembly and configuration
When assembling a voltmeter, it is important to ensure that the microprocessor itself is installed correctly (it must already be programmed). To do this, you need to find the marking of its first leg on the body and, in accordance with it, fix the product body in the mounting holes.
Important! Only after you have complete confidence in the correct installation of the most important part, you can proceed to soldering it (“fitting on solder”).
Sometimes, to install a microcircuit, it is recommended to solder a special socket under it into the board, which significantly simplifies all working and configuration procedures. However, this option is beneficial only if the socket used is of high quality and ensures reliable contact with the legs of the microcircuit.
After soldering the microprocessor, you can fill and immediately place all other elements of the electronic circuit on the solder. During the soldering process, the following rules should be followed:
- Be sure to use an active flux that promotes good spreading of liquid solder over the entire landing area;
- Try not to hold the tip in one place for too long, which will prevent overheating of the mounted part;
- Upon completion of soldering, be sure to wash the printed circuit board with alcohol or any other solvent.
If no errors were made when assembling the board, the circuit should work immediately after connecting power to it from an external source of stabilized voltage of 5 Volts.
In conclusion, we note that your own power supply can be connected to the finished voltmeter after completing its configuration and testing, carried out according to standard methods.
Video
Digital VOLTMETER and AMMETER for laboratory power supply (unipolar and bipolar) on a specialized ICL7107 chip
It so happened that there was a need to manufacture an ammeter and a voltmeter for laboratory power supplies. To solve the problem, I decided to scour the Internet and find an easily repeatable scheme with an optimal price-quality ratio. There were thoughts of making an ammeter and a voltmeter from scratch based on an LCD and a microcontroller (MK). But I think to myself, if it’s a microcontroller, then not everyone will be able to repeat the design - after all, you need a programmer, and I don’t even really want to buy or make a programmer for programming once or twice. And people probably won’t want it either. In addition, all microcontrollers (that I have dealt with) measure the positive polarity input signal relative to the common wire. If you need to measure negative values, you will have to deal with additional operational amplifiers. Somehow all of this was stressful! My eye fell on the widespread and affordable ICL7107 chip. Its cost turned out to be half the cost of MK. The cost of a 2x8 character LCD turned out to be three times more than the cost of the required number of seven-segment LED indicators. And I like the glow of LED indicators more than LCD. You can also use a similar, even cheaper, domestically produced m/skh KR572PV2. I found the diagrams on the Internet and went ahead to check the functionality! There was an error in the diagram, but it was corrected. It turned out that when calibrating the readings, the m/sx ADC works quite accurately and the accuracy of the readings will completely satisfy even the most picky user. The main thing is to take a good quality multi-turn tuning resistor. The counting is very fast - without brakes. There is a significant drawback - bipolar power supply ±5V, but this issue can be easily solved using a separate mains power supply on a low-power transformer with positive and negative stabilizers (I will give the diagram later). To obtain -5V, you can use a specialized ICL7660 microcircuit (visible in the photo at the top of the page) - cool stuff! But it has an adequate price only in an SMD package, and in a regular DIP it seemed to me a little expensive, and it’s much more difficult to buy than conventional linear stabilizers - it’s easier to make a negative stabilizer. It turned out that the ICL7107 perfectly measures both positive and negative voltages relative to the common wire, and even the minus sign is displayed in the first digit. In fact, in the first digit only the minus sign and the number “1” are used to indicate the polarity and value of hundreds of volts. If for a laboratory power supply a voltage indication of 100V is not needed and there is no need to indicate the voltage polarity, since everything should be written on the front panel of the power supply, then the first indicator can not be installed at all. For an ammeter the situation is the same, but only a “1” in the first digit will indicate that a current of ten Amperes has been reached. If the power supply has a current of 2...5A, then you can not install the first indicator and save money. In short, these are just my personal thoughts. The schemes are very simple and start working right away. You only need to set the correct readings on the control voltmeter using a trimming resistor. To calibrate the ammeter, you will have to connect a load to the power supply and use the control ammeter to set the correct readings on the indicators and that’s it! To power ammeters in a bipolar power supply circuit, it turned out that it is best to use a separate small network transformer and stabilizers with a common wire isolated from the common wire of the power supply itself. In this case, the inputs of the ammeters can be connected to the measuring shunts “at random” - m/sx will measure both “positive” and “negative” voltage drops on the measuring shunts installed in any part of the power supply circuit. This is especially important when both stabilizers in a bipolar power supply are already connected via a common wire without measuring shunts. Why do I want to make a separate low-power power supply for meters? Well, also because if you power the meters from the transformer of the power supply itself, then when you receive a voltage of 5 V out of 35 V, you will need to install an additional radiator, which will also generate a lot of heat, so it’s better to use small sealed transformers on a small board. And in the case of a power supply with a voltage of more than 35 V, say 50 V, you will have to take additional measures to ensure that for five Voltage stabilizers at the input the voltage is no more than 35 V. You can use high-voltage switching stabilizers with low heat generation, but this increases the cost. In short, if not one thing, then another ;-)
Voltmeter circuit:
Ammeter circuit:
Photo view of the printed circuit board of a voltmeter and ammeter (board size 122x41 mm) with seven-segment LED indicators of type E10561 with digits 14.2 mm high. The power supply for the voltmeter and ammeter is separate! This is necessary to ensure the ability to measure currents in a bipolar power supply. The ammeter shunt is installed separately - a 0.1 Ohm/5 W cement resistor.
Scheme of the simplest mains power supply for joint and separate power supply of voltmeters and each of the ammeters (maybe a nonsense idea, but it works):
And a photo view of printed circuit boards using compact sealed transformers 1.2...2 W (board size 85x68 mm):
Voltage polarity converter circuit (as an option for obtaining -5 V from +5 V):
Video of voltmeter operation
Video of workammeter
I won’t make kits or boards, but if anyone is interested in this design, you can download the printed circuit board drawings.
Thank you all for your attention! Good luck, peace and goodness to your home! 73!
Many home electricians are dissatisfied with industrial production testers, so they think about how to, as well as how to improve the functionality of the industrial production tester. For this purpose, a special shunt can be made.
Before you begin, you should calculate the shunt for the microammeter and find a material with good conductivity.
Of course, for greater measurement accuracy, you can simply purchase a milliammeter, but such devices are quite expensive, and they are rarely used in practice.
Recently, testers designed for high voltage and resistance have appeared on sale. They do not require a shunt, but their cost is very high. For those who use a classic tester made in Soviet times, or use a homemade one, a shunt is simply necessary.
Selecting a current ammeter is not an easy task. Most devices are produced in the West, in China or in the CIS countries, and each country has its own individual requirements for them. Also, each country has its own permissible values of direct and alternating current, requirements for sockets. In this regard, when connecting a Western-made ammeter to domestic equipment, it may turn out that the device cannot correctly measure current, voltage and resistance.
On the one hand, such devices are very convenient. They are compact, equipped with a charger and easy to use. A classic dial ammeter does not take up much space and has a visually clear interface, but it is often not designed for the existing voltage resistance. As experienced electricians say, there are “not enough amperes” on the scale. Devices designed in this way necessarily require shunting. For example, there are situations when you need to measure a value up to 10a, but there is no number 10 on the instrument scale.
Here are the main ones disadvantages of a classic factory ammeter without a shunt:
- Large error in measurements;
- The range of measured values does not correspond to modern electrical appliances;
- Large calibration does not allow small quantities to be measured;
- When trying to measure a large resistance value, the device goes off scale.
A shunt is necessary in order to correctly measure in cases where the ammeter is not designed to measure such quantities. If a home craftsman often deals with such quantities, it makes sense to make a shunt for an ammeter with your own hands. Shunting significantly improves the accuracy and efficiency of its work. This is an important and necessary device for those who often use the tester. It is usually used by owners of the classic 91s16 ammeter. Here are the main advantages of a homemade shunt:
Manufacturing procedure
Even a freshman at a vocational school or a novice amateur electrician can easily handle making a shunt on his own. If connected properly, this device will greatly increase the accuracy of the ammeter and will last a long time. First of all, it is necessary to calculate the shunt for a DC ammeter. You can learn how to make calculations via the Internet or from specialized literature addressed to home electricians. You can calculate the shunt using a calculator.
To do this, you just need to substitute specific values into the finished formula. In order to use the calculation scheme, you need to know the real voltage and resistance for which a particular tester is designed, and also imagine the range to which you need to expand the capabilities of the tester (this depends on which devices a home electrician most often has to deal with ).
Perfect for making such materials:
- Steel clip;
- Roll of copper wire;
- Manganin;
- Copper wire.
You can purchase materials in specialized stores or use what you have at home.
In fact, a shunt is a source of additional resistance, equipped with four clamps and connected to the device. If steel or copper wire is used to make it, do not twist it into a spiral.
It is better to carefully lay it in the form of “waves”. If the shunt is sized correctly, the tester will perform much better than before.
The metal used to make this device must conduct heat well. But inductance, if a home electrician is dealing with the flow of a large current, can negatively affect the result and contribute to its distortion. This also needs to be kept in mind when making a shunt at home.
If a home electrician decides to purchase a commercially available ammeter, he should choose one with a fine calibration because it will be more accurate. Then, perhaps, you won’t need a homemade shunt.
When working with the tester, you should follow basic safety precautions. This will help prevent serious injury caused by electrical shock.
If the tester systematically goes off scale, you should not use it.
It is possible that the device is either faulty or is not able to show the correct measurement result without additional equipment. It is best to purchase modern, domestically produced ammeters, because they are better suited for testing new generation electrical appliances. Before you start working with the tester, you should carefully read the operating instructions.
A shunt is a great way to optimize the work of a home electrician when testing electrical circuits. In order to make this device with your own hands, you will only need a working industrial production tester, available materials and basic knowledge in the field of electrical engineering.
♦ In the previous article: to control the charging current it is used ammeter for 5 - 8 amperes.
An ammeter is a rather scarce thing and you can’t always find one for such a current. Let's try to make an ammeter with our own hands. 
To do this, you will need a pointer measuring device of the magnetic-electric system for any current of the full deviation of the needle on the scale.
It is necessary to ensure that it does not have an internal shunt or additional resistance for the voltmeter.
♦ The measuring pointer device has an internal resistance of the movable frame and the current of the full deflection of the pointer. The pointer device can be used as a voltmeter (additional resistance is connected in series with the device) and as an ammeter (additional resistance is connected in parallel with the device).
♦ The circuit for the ammeter is on the right in the figure.
Additional resistance - shunt calculated using special formulas... We will make it in a practical way, using only a calibration ammeter on current up to 5 - 8 amperes, or by using a tester, if it has such a measurement limit.
♦ Let's assemble a simple circuit from a charging rectifier, a standard ammeter, a wire for a shunt and a chargeable battery. See the picture... 
♦ A thick wire made of steel or copper can be used as a shunt. The best and easiest way is to take the same wire that was used to wind the secondary winding, or a little thicker.
You need to take a piece of copper or steel wire about 80 centimeters, remove the insulation from it. At two ends of the segment, make rings for bolt fastening. Connect this segment in series with a reference ammeter.
Solder one end from our pointer device to the end of the shunt, and run the other along the shunt wire. Turn on the power, set the charge current using the regulator or toggle switches according to the control ammeter - 5 amp.
Starting from the soldering point, run the other end from the pointer device along the wire. Set the readings of both ammeters to the same level. Depending on the frame resistance of your pointer gauge, different pointer gauges will have different shunt wire lengths, sometimes up to one meter.
This, of course, is not always convenient, but if you have free space in the case, you can carefully place it.
♦ The shunt wire can be wound into a spiral as in the figure, or in some other way depending on the circumstances. Stretch the turns a little so that they do not touch each other, or put rings made of vinyl chloride tubes along the entire length of the shunt. 
♦ You can first determine the length of the shunt wire, and then use insulated wire instead of bare wire and wind it in bulk onto the workpiece.
You must select carefully, performing all operations several times, the more accurate the readings of your ammeter will be.
The connecting wires from the device must be soldered directly to the shunt, otherwise the device arrow will read incorrectly.
♦ The connecting wires can be of any length, and therefore the shunt can be located anywhere in the rectifier body.
♦ It is necessary to select a scale for the ammeter. The ammeter scale for measuring direct current is uniform.