Situations when a voltmeter must be at hand, there are often enough. For this there is no need to use the factory complex device. Make a simple voltmeter with your own hands - not a problem, because it consists of two elements: the armerus unit and the resistor. True, it should be noted that the suitability of the voltmeter is determined by its input resistance, which consists of resistances of its elements.
But it is necessary to take into account the fact that the resistors are different with different rating, and this suggests that the input resistance will depend on the installed resistor. That is, picking up a relative resistor, you can make a voltmeter for measurements of certain voltage levels of networks. The measuring device itself is more often estimated by the indicator - the relative input resistance, which comes on one volt of the voltage, its unit of measure - com / c.
That is, it turns out that the input resistance on different measured areas is different, and the relative value is a permanent indicator. In addition, the less the arrow of the measuring unit is deflected, the greater the relative value, and, it means that the measurements will be more accurate.
Device for measuring several limits
Who more than once came across transistor structures and schemes knows that very often a voltmeter has to measure the chains with tens of dozens of one volt to hundreds of volts. A simple tidward, made with your own hands, this does not master with one resistor, so in the scheme you will have to connect multiple elements with different resistance. So that you understand what we are talking about, we suggest familiarizing yourself with the scheme located below:
It shows that there are four resistors in the diagram, each of which is responsible for its measurement range:
- From 0 volts to one.
- From 0 volts to 10v.
- From 0 to 100 volts.
- From 0 to 1000 V.
The nominal value of each resistor is calculated by calculation, which is carried out on the basis of the Ohm law. Here is the following formula:
R \u003d (UP / IIS) -PP, where
- RP is the resistance of the measuring unit, take, for example. 500 ohms;
- UP is the maximum voltage of the measured limit;
- II is the power of the current at which the arrow deflects to the end of the scale, in our case - 0.0005 amps.
For a simple voltmeter from a Chinese ammeter, you can choose the following resistors:
- for the first limit - 1.5 com;
- for the second - 19.5 com;
- for the third - 199.5;
- for the fourth - 1999.5.
But the relative magnitude of the resistance of this device will be 2 kΩ / c. Of course, the estimated rates do not coincide with the standard, so the resistors will have to pick up close ones. Next, the finish fit is carried out, at which the device is graded.
How to remake the voltmeter of constant voltage into the variable
The scheme shown in Figure 1 is a DC voltmeter. To make it variable or, as specialists say, pulsating, it is necessary to install a rectifier in the design, with which the constant voltage is converted into a variable. Figure 2, the voltmeter of alternating current is shown schematically.
This scheme works like this:
- when there is a positive half-wave on the left clamp, the diode d1, d2 opens in this case;
- voltage passes through the ammeter to the right clamp;
- when the positive half-wave is at the right end, then D1 is closed, and the voltage through the ammeter does not pass.
The diagram is necessarily added resistor RD, the resistance of which is calculated in the same way as the remaining elements. True, its settlement value is divided into a coefficient equal to 2.5-3. This is if a single-alpapid rectifier is installed in a voltmeter. If a two-speech rectifier is used, the resistance value is divided into the coefficient: 1.25-1.5. By the way, the latter scheme is depicted in Figure No. 3.
How to connect a voltmeter
The one who does not know, but wants to check the tension on a site of an electrical network, should wonder - how to connect a voltmeter? This is actually a serious question, in the response of which lies a simple requirement - the voltmeter connection must be carried out only in parallel load. If a sequential connection is made, the device itself simply fails, and you can be powder.
The fact is that with such a connection, the current is reduced acting on the measuring instrument itself. With this resistance, it does not change, that is, it remains great. By the way, never confuse a voltmeter with an ammeter. The latter connects to the chain sequentially to reduce the resistance rate to a minimum.
And the last question of the topic - how to use a voltmeter made by yourself. So, in your device two probe. One connects to the zero contour, the second to the phase. You can also check the voltage through the outlet, having previously determined, to which nest is driven by zero, and to which phase. Or connect parallel to the device to the measured area. The arrow of the measuring unit will show the voltage in the network. This is how this homemade measuring instrument is used.
Hello expensive reader. Sometimes there is a need to have a small simple voltmeter "at hand". Make such a voltmeter do it yourself will not be a lot of work.
The suitability of the voltmeter for measuring stresses in certain circuits is judged by its input resistance, which consists of resistance to the frame of the direction of the direction of the direction and the resistance of the adding resistor. Since on different limits, additional resistors have different nominal ratings, then the input resistance of the device will be different. More often a voltmeter is estimated by its relative input resistance characterizing the ratio of the input resistance of the device to 1B of the measured voltage, for example 5k / c. It is more convenient: the input resistance of the voltmeter along different limits of measurements is different, and the relative input resistance is constant. The smaller the total deviation of the arrow of the measuring instrument II used in the voltmeter, the greater the relative input resistance will be, the more accurate measurements will be produced by it. In transistor structures, it is necessary to measure the voltage from the voltage of up to several tens of volts, and even more in the lamps. Therefore, a single-cost voltmeter is inconvenient. For example, a voltmeter with a scale of 100V cannot be accurately measured even the voltages 1-2V, since the deviation of the arrow will be low. Therefore, a voltmeter is needed, which has at least three - four dimensions limit. The diagram of such a DC voltmeter is shown in Fig. 1. The presence of four additive resistors R1, R2, R3 and R4 indicates that the voltmeter has four dimensions limit. In this case, the first limit is 0-1V, the second 0-10V, the third 0-100v and the fourth 0-1000v.
The resistance of the addition resistors can be calculated by the formula resulting from the Ohm law: Rd \u003d UP / II - RP, here the UP is the largest voltage of this measurement limit, II is a total deflection of the arrow of the measuring head, and RP is the resistance of the measuring head frame. For example, for a device for a current of II \u003d 500MK (0.0005a) and a frame resistance of 500 Ohm, the resistance of the added resistor R1, for the limit of 0-1V should be 1.5k, for the limit of 0-10V - 19,5k, for limit 0 -100B - 199.5, for the limit of 0-1000 - 1999,5. The relative input resistance of such a voltmeter will be 2kom / c. Usually, an additional resistors with ratings close to the calculated are mounted in a voltmeter. Finally, the "fit" of their resistance is produced during a voltmeter graduation by connecting to them parallel or sequentially other resistors.
If a direct current voltmeter is supplemented with a rectifier that converts alternating voltage to constant (more precisely - pulsating), we obtain a voltmeter of alternating current. A possible diagram of such a device with a single-altariodic rectifier is shown in Fig.2. The device works as follows. In those moments of time when on the left (according to the scheme), the climate of the device is a positive half-wave of alternating voltage, the current goes through the diode D1 and then through the microammeter to the right clamp. At this time, the diode d2 is closed. During a positive half-wave on the right clamp, the diode D1 is closed, and the positive half-wave of alternating voltage closes through a diode d2, bypassing the microammeter.
The addition resistor of the RD is calculated in the same way as for constant voltages, but the resulting result is divided by 2.5-3, if the rectifier of the device is single-alternating, or 1.25-1.5 if the rectifier of the device is double-wire - Fig. 3. More accurate resistance of this resistor is selected by an experimental way during the graduation of the scale of the instrument. You can calculate RD and for other formulas. The resistance of the added resistors of the rectifying system voltmeters, made according to the scheme in Fig.2, are calculated by the formula:
Rd \u003d 0.45 * UP / II - (RP + RD);
For the scheme in Fig.3, the formula has the form:
Rd \u003d 0.9 * UP / II - (RP + 2D); where Rd is the resistance of the diode in the forward direction.
The readings of the rectifying system devices are proportional to the average rectified values \u200b\u200bof the measured stresses. The scales are graded in the mean square values \u200b\u200bof the sinusoidal voltage, so the readings of the rectifying system devices are equal to the range of voltage only when measuring the stresses of the sinusoidal shape. The D9D German diode diodes are used as rectifier diodes. Such voltmeters can measure sound frequency voltage to several tens of kilohertz. The scale for a homemade voltmeter can be drawn using the FrontDesigner_3.0_setup program.
For digital voltage control and current in the power supply, it is not necessary to make the ADC and indicator itself. For this purpose, the Chinese multimeter costs 3-4 dollars is quite suitable, which is comparable to the cost of making their own digital indication.
For alteration, a popular M830B was selected. Below in detail, in the pictures, the alteration of a multimeter is painted to indicate the voltage and current in your power supply.
The basic meaning of the alteration was to reduce the size of the board with the indicator, i.e. Just part of the board had to be cut off. For the alteration, the simplest and cheapest Chinese multimeter M830B was purchased. M830B multimeter circuit can be downloaded in our file archive. The measurement limit of the voltage of our design will be 200 B, and the current limit is 10 A. To select the measurement mode "Voltage" - "Current", the S1 switch is used with two contact groups. The diagram shows the position of the switch in the voltage measurement mode.
First you need to disassemble the multimeter and pull out the board. View of the board from the part side you can see on the photo.
And here the photo board from 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 second board scheme is shown in the picture. The divisor resistors use the dropped resistors from the Multimeter Board. Their designation in the diagram corresponds to the notation on the M830B multimeter board. Also, the diagram provides additional explanations. Letters in circles correspond to the points of connection of one board to the other. A low-power voltage stabilizer is used to power the design, which is connected to a separate transformer winding.
Actually proceed. We drop R18, R9, R6, R5. Resistors R6 and R5 Save for the input part of our design. Cut off the upper contact R10 from the schema and cut out a part of the track (on the photo is marked with cross). We drop R10. We drop R12 and R11.
R12 and R11 connect sequentially. And solder with one end to the upper contact R10, and the track cut off from R10. We drop up R20 and sear it in place R9. We drop R16 and drill new holes for it (see photo)
We solder R16 to a new place.
And here the view of the R16 solder from the indicator.
We take scissors for metal and cut off part of the board.
I turn the board with the indicator to yourself. Middle from the indicator Contact R9 (now there is R20) cut off from the scheme (marked with a cross). The distance from the indicator contacts R9 (now there is R20) and R19 connect together (from the indicator side), on the photo indicated by a red jumper. The upper contact R10 (there is now R11 and R12) connect with the lower contact R13, the photo indicates the red jumper. We remove part of the tracks marked with crosses. And solder the jumper to the neighbor from the R9 contact indicator (now there is R20), instead of a remote track.
We remove the tracks marked by the cross, and prepare the contact pins for the decay with the second board, on the photo are shown by arrows.
We solder the jumper. Complete contact wires from the second board, observing the correspondence of the letters (A-A, B-B, etc.)
Everything! The design is assembled, proceeding to check. Connect to the power source and measure the battery voltage. Works!
On this photo, the design is built into the power supply unit for which it was created. When the load is connected, pressing the "Voltage-current" button, the value of the flowing current is displayed on the indicator.
Prelude
Studying somehow endless expanses of the Internet for Chinese utility, I came across a digital voltmeter module:The Chinese "rolled out" such TTX: 3-Digit Red Color Display; Voltage: 3.2 ~ 30V; Working Temperature: -10 ~ 65 "C. Application: Voltage Testing.
I didn't quite fit me in the power supply (testimony not from zero - but it is a payroll for meals from the measured chain), but inexpensive.
I decided to take and deal in place.
Voltmeter Module Scheme
At the calibration, the module was not so bad. The indicator dropped out, sized the scheme (detail numbering is shown conditionally):Unfortunately, the chip remained unidentified - the marking is absent. Perhaps this is some kind of microcontroller. The nominal capacitor C3 is unknown, it did not fall out. C2 - presumably 0.1 mk, also did not fall out.
Process with a fairy to a place ...
And now about the modifications that are necessary to bring this "recent" to mind.
1. So that it starts to measure the voltage of less than 3 volts, you need to drop the resistor-jumper R1 and to its right (according to the scheme) the contact pad is 5-12V from an external source (above can, but undesirable - the DA1 stabilizer is greatly heated). Minus external source to apply for a common scheme wire. The measured voltage is submitted to the standard wire (which was originally soldered by the Chinese).
2. After refinement according to claim 1, the range of the voltage is increased to 99.9V (previously it was limited to the maximum input voltage of the DA1 - 30B stabilizer). The input divider coefficient is about 33, which gives us the maximum of 3 volts at the input DD1 at 99.9V at the divider entrance. I filed a maximum of 56V - I don't have anymore, I did not burn anything :-), but also increased error.
4. To move or completely turn off the point, you need to drop the R13 10kum chip-resistor, which is located next to the transistor and instead to secure a regular resistor 10K. 0.125WB between the long-range chip-resistor with a contact pad and the corresponding control segment DD1 - 8, 9 or 10.
The poverty point is evolving on the average number and the database of the VT1 transistor, respectively, through the 10K chip is connected to an output. 9 DD1.
The current consumed by the voltmeter was about 15th and changed depending on the number of illuminated segments.
After the described alteration, all this current will be consumed from an external power source, without loading the measured chain.
TOTAL
And in conclusion, a few more photos of the voltmeter.
Factory condition
With drop-down indicator, front view
With a drop-down indicator, rear view
The indicator is toned with automotive tinting film (20%) to reduce brightness and improve the visibility of the indicator into the light.
I highly recommend it to toned. Tinning film trimming will be happy to give you free in any car service tinting.
Also, there are other modifications of this module on the Internet, but the essence of rework does not change - if you caught not such a module, simply adjust the circuit on the board, dropping the indicator or ringing the chain to the tester and forward!
Received with Aliexpress Parc of electronic built-in voltmeters model V20D-2P-1.1 (DIMENT DISTRICT), the price of the question 91 cent is a piece. In principle, you can now find it cheaper (if you look good enough), but not the fact that it will not be to the detriment of the quality of the assembly of the device. Here is its characteristics:
- operating range 2.5 V - 30 V
- red glow color
- overall size 23 * 15 * 10 mm
- additional nutrition does not require (two-wire)
- it is possible to adjust
- update frequency: about 500 ms / time
- the promised measurement accuracy: 1% (+/- 1 discharge)
And everything would be fine, put on the place and used, but I got into my eyes information about the possibility of their refinement - adding the current measurement function.
Digital Chinese Voltmeter Prepared everything you need: two-pole toggle switch, output resistors - one MLT-1 per 130 com and the second wire 0.08 ohms (made from the nichrome spiral with a diameter of 0.7 mm). And a whole evening according to the found scheme and guidelines for its implementation combined this economy with a voltmeter. To no avail. Like degradation in the understanding of the underwent and unacked in the found material was not enough, whether there were differences in the schemes. Voltmeter did not work in any way.
Connect the digital voltmeter module I had to drain the indicator and study the scheme. There was no longer a small soldering iron, but a mahony, so that she was pretty. But within the next five minutes, when the whole scheme became available to the review, I understood everything. In principle, he knew that it was necessary to start, but I really wanted to solve the issue of "easy".
V-meter refinement scheme
Refinement scheme: ammeter in a voltmeter So this scheme was born to connect additional electronic components with already existing in the voltmeter scheme. The standard resistor of the circuit marked in blue is subject to mandatory removal. I will say right away from other schemes on the Internet found, for example, the connection of the trimmed resistor. I did not redraw the entire voltmeter scheme (I'm not going to repeat), drawn only the part that is necessary for refinement. The fact that the power of the voltmeter needs to be done separately consider it obvious, after all, the beginning of the reference in the testimony should begin with scratch. In the future, it turned out that the battery or battery nutrition is not suitable, because the current consumption of the voltmeter at a voltage of 5 volts is 30 mA.
Board - Module Chinese Voltmeter After assembly, the voltmeter took the essence of the action. I will not be wonderful, I'll just show you and tell you what to connect with that everything happens.
Step-by-step instruction
so, first action - SMD Resistor resistance resistor 130 is dropped from the circuit at the inlet of the positive power supply, between the diode and the stroke resistor 20 kΩ.
Connect the resistor to the Voltmeter ammeter Second. On the released contact, from the editorial side, the Wire of the desired length is soldered (for sample it is convenient for 150 mm and better than red)
Run smm resistor Third. The track connecting the resistor 12 com and the condenser, with the "earth" side the second wire (for example, blue) is soldered.
Testing a new scheme
Now, according to the schema and this photo, "hang" on a voltmeter Supplement: toggle switch, fuse and two resistors. Here, the main thing is to properly fall the newly installed red and blue wires, however, not only them.
Voltmeter block alternate in a - meter And here there are more wires, although everything is simple:
"- A pair of connecting wires connected E / engine« separate power Voltmeter"- battery with two more wires
« power supply output"- another couple of wires
After supplying power to the voltmeter immediately, "0.01" was immediately high, after the power supply to the electric motor, the meter in the voltmeter mode showed the voltage at the output of the power supply unit is 7 volt, then switched to the ammeter mode. Switching performed when the power supply is disconnected. In the future, instead of a toggle, I will put a button without fixing, so safer for the schema and more convenient for operation. I was pleased with the fact that everything worked with the first attempt. However, the ammeter readings were different from indications on a multimeter more than 7 times.
Chinese voltmeter - ammeter after alteration It turned out that the wire resistor instead of the recommended resistance of 0.08 ohms has 0.8 ohm. It was mistaken in the measurement when it was made in the zeros count. It was out of the position: the crocodile with a minus wire from the load (both black) moved along the straightened nichrome spiral in the direction of the input from the power unit, the moment when the readings of the multimeter and the modified now the ampervoltmeter coincided and became the moment of truth. The resistance of the involved portion of the nichrome wire was 0.21 ohms (measured the prefix to the multimeter at the limit "2 ohms"). So it didn't even feel bad that instead of 0.08 resistor turned out to be 0.8 ohms. Here, as not counting, according to the formulas, you still have to customize. For clarity, the result of his hassle was recorded on a video.
Video
I consider the acquisition of voltmeter data successful, that's just a pity that their current price in that shop has greatly grown, without a small $ 3 per a piece. By Babay Iz Barnaula.
