Connecting a VFD indicator from an old Soviet tape recorder to a computer. Pointer instruments - indicators How to make a voltmeter from a tape recorder recording indicator

ХР1 R1 Ш R2* 51X

How to “stretch” the bar of a voltmeter. By controlling some kind of tension. sometimes it is necessary to either monitor its fluctuations or measure it more accurately. Let's say, when operating a car battery, it is important to monitor the change in its voltage in the range of 12.. L 5 V. It is this range that would be desirable to place on the entire scale of the voltmeter dial indicator. But. As you know, the reading on any of the ranges of almost all measuring instruments starts from zero and it is impossible to achieve a higher reading accuracy in the area of ​​interest.

And yet, there is a way to “stretch” almost any part of the scale (beginning, middle, end) of a DC voltmeter. To do this, you need to take advantage of the PROPERTY of the zener diode to open at a certain voltage equal to the stabilization voltage. For example, to stretch the end of the scale of the range 0...15 V, it is enough to use a zener diode in the same role as in the previous experiment.

Take a look at fig. 4. Zener diode VD1 is connected in series with a single-limit voltmeter, composed of a dial indicator PA1 and an additional resistor R2. As in the previous experiment, the zener diode “eats” part of the measured voltage, equal to the stabilization voltage. As a result, the voltmeter will receive a voltage exceeding the stabilization voltage.

FOR IRADIG-BEGINNERS"_

This voltage will become a kind of reference zero, which means that only the difference between the highest measured voltage and the stabilization voltage of the zener diode will “stretch” on the scale.

The device shown in the figure is designed to control battery voltage in the range from 10 to 15 V. But this range can be changed at will by appropriate selection of the zener diode and resistor R2.

What is the purpose of resistor R1? In principle, it is not required. But without it, while the zener diode is closed, the indicator needle remains at the bullet mark. The introduction of a resistor allows you to observe a voltage of up to 10 V in the initial section of the scale, but this section will be greatly “compressed”.

Having assembled the parts shown in the diagram and connecting them with the dial indicator PA1 (micro ammeter M2003 with a full pointer deflection of 100 μA and an internal resistance of 450 Ohms), connect the XP1 and XP2 probes to a power supply with an adjustable output voltage. Smoothly increasing the voltage to 9...9.5 V, you will notice a slight deviation of the indicator needle - just a few divisions at the beginning of the scale. As soon as, with a further increase in voltage, it exceeds the stabilization voltage, the angle of deflection of the needle will increase sharply. From approximately 10.5 to 15 V, the needle will pass almost the entire scale.

To verify the role of resistor R1, disconnect it and repeat the experiment. Up to a certain input voltage, the indicator needle will remain at zero.

You may be interested in this method of “stretching” the scale and want to practically implement it to control other voltages. Then you will have to use simple calculations. The initial data for them will be the voltage measurement range (l)m>x), the total deflection current of the indicator needle (11Pax), the initial reference point current (1pc) and the corresponding reference voltage (UIIljn).

For example, let's calculate* our device shown in the diagram. Let's say that the entire circuit of the device CImex = 100 μA) is intended to control voltages from 10 to 15 V, but the countdown will begin from the division corresponding to the current YumkA (1Ш)П = 10 μA), and therefore a voltage of 10.5 V (Urnin = = 10.5 V).

First, we determine the coefficients p and k, which will be needed for subsequent operations:

P=lmi„/ln,“= 10/100=0.1; k=Um,„/Un,„>=)0.S/15=0.7.

Calculates the required stabilization voltage of the future zener diode:

UrT=Uninx(k-p)/(l-p) =

15*0.6/0.9=10 V.

Zener diodes D810 and D814V have this voltage (see reference table in the article “Zener diode”).

We determine the resistance of resistor R2 in kilo-ohms, expressing the current in milliamps. R2=U,nax(l-K)/lmils(l-p) =

15.0.3/0.1-0.9=50 kOhm.

In general, the internal resistance of the dial indicator (450 Ohms) should be subtracted from the obtained value, but this is not necessary, but the resistance of resistor R2 is selected practically when setting up the voltmeter.

Finally, determine the resistance of resistor R1: Rl = Uer/p.lmax=10/0.1 = 1000 kOhm=1 MOhm.

V. MASLAYEV

Zelenograd

Visibility is a big deal. So popular wisdom says: “It’s better to see once than to hear a hundred times.” And in electronics, where the ongoing processes in the operation of a particular device are often confirmed indirectly, or even generally implied and even taken on faith, it is generally difficult to overestimate the visual display. It is not for nothing that oscilloscopes are so revered among radio amateurs, giving them the opportunity to “look” even into the process. But I won’t talk about the complex - I’d like to deal with the simple ones. I have assembled almost a dozen different chargers, and to charge batteries I increasingly use a simple laboratory power supply that has an output voltage and current. The measuring heads clearly inform how many volts and milliamps go to the battery being charged. But it’s not possible to use them everywhere; even the smallest of them will often still be prohibitively large for many amateur radio homemade products. But dial indicators from tape recorders and other radio devices of the last century, which have not been sold out in the bazaars to this day, will be just right here. Here are some of them:

Designed for operation in DC circuits, at any scale position. Total deflection current (depending on model) 40 - 300 µA. Internal resistance 4000 Ohm. Scale length - 28 mm, weight 25 g.

Designed to work with the scale in a vertical position. Deviation current 220 - 270 µA. Internal resistance 2800 Ohm. Dimensions 49 x 45 x 32 mm. Scale length - 34 mm.

designed to work at any scale position. The total deviation current is no more than 250 µA. Internal resistance 1000 Ohm. Dimensions 21.5 x 60 x 60.5 mm. Weight 30 gr. These indicators and others like them are united by:

• small size
• simplicity of design
• low cost
• and, of course, the principle of operation

The operating principle is based on the interaction of two magnetic fields. The fields of a permanent magnet and the field formed by a current passing through a frameless frame, which consists of a large number (115 - 150) turns of copper wire with a diameter of only 8 - 9 microns. Without delving into the nuances, we can name two main actions that need to be performed in order to make it possible to use the existing indicator:

1. Equip it with a shunt or additional resistance (used to change the upper limit of measurement), depending on how you will use it (voltmeter / ammeter).
2. Make a new scale.

Discuss the article POINT INSTRUMENTS - INDICATORS

On the pages of Parkflyer, modelers often raise the topic of promptly checking the serviceability of the RU transmitter and its antenna, which is the most important point in the reliability of the interaction between the transmitter and the receiver during flights of RU models.
To check the serviceability of the transmitter and its antenna, I use a simple homemade Electromagnetic Field Indicator, which I made from a dial indicator of the recording level from an old tape recorder. The indicator turned out to be very small, smaller than a matchbox and easily fits in the breast pocket of a shirt, which allows you to monitor the radiation of the transmitter and the serviceability of its antenna at any time right in the field.

The dial indicator for recording a tape recorder is a microammeter with a deflection current of 50....100 µA.
To make the Indicator, in addition to the head, you need two microwave diodes; I used KD514A diodes. A half-wave section of a suitable wire Ø 1 mm is used as an antenna. For 2.4 GHz RU transmitters, the length of the segment is 60 mm. The circuit diagram of the device is simple.

Solder the diodes to the indicator terminals. This is what KD514A diodes look like.

Ready device.

The antenna is glued with epoxy not directly to the indicator body, although it is made of plastic, but through a piece of strip. The fact is that the instrument scale is drawn on a metal plate, which is attached to the back cover inside the case, and if the antenna is glued directly to the cover, it will be located in close proximity to the metal scale at a distance of 1.5 mm from it, separated by a plastic bottom. As a result, a small capacitance appears between the metal scale and the antenna (but the frequency is 2400 MHz!), which significantly reduces the sensitivity of the indicator - the arrow deviates by a smaller angle, and if you make a gap of 6...8 mm, then the capacitance becomes negligible and the arrow deviates by big angle. Therefore, I had to make a gap from a piece of slats. This nuance was revealed during the manufacture of the Field Indicator.

Here is a video showing the practical application of the Indicator.

To make a Field Indicator, any microammeter with a current of 50....100 µA is suitable, not necessarily from a tape recorder. This will only affect the size of the device.

Here are good M4206 100 µA heads, but they are currently difficult to find.

You can also use other microwave diodes, for example: KD503, D403, D405, D605, D20.

A good microwave diode is obtained from a GT346 transistor with a collector closed to the base.
It is located in the ancient SKD-24, is quite sensitive and operates up to 2.4 GHz and higher.
Happy flights and soft landing everyone!

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.