How to make a voltmeter from an indicator from a tape recorder. Connecting a VFD indicator from an old Soviet tape recorder to a computer. Why one device cannot measure a wide range of quantities

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. For example, 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, reading on any of the ranges of almost all measuring instruments goes from zero and achieve more high precision reading in the area of ​​interest is impossible.

And yet, there is a way to “stretch” almost any part of the scale (beginning, middle, end) of a voltmeter DC. 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, as long as the zener diode is closed, the indicator arrow 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 (1Sh)P = 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.

Counts required voltage stabilization 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

To visually assess the strength of the charging current, I will need a device for measuring current strength - an ammeter. Since we didn’t have anything useful at hand, we’ll use what we have. And this “what is” is a common indicator from old Soviet radios. Since the indicator reacts to very small currents, it is necessary to make a shunt for it.

Shunt- this is a conductor with a certain resistivity, which is connected to the current measuring device in parallel. At the same time, it passes through itself or shunts most of the electric current. As a result, the rated current calculated for it will pass through the meter device. To understand how currents flow in circuit nodes, we study Kirchhoff’s laws.

In order to calculate the shunt for an ammeter, I will need some parameters of the measuring head (indicator): frame resistance ( Rram), the current value at which the indicator needle deviates maximum ( Iind) and the upper current value that the indicator should measure in the future ( Imax). We take 10 A for the maximum measured current. Now we need to determine Iind, which is achieved experimentally. But for this you need to assemble a small electrical circuit.

Using resistor R1, we achieve the maximum deviation of the indicator needle and take these readings from the tester PA1. In my case, Iind = 0.0004 A. Frame resistance Rram We also measured it using a tester, which was 1 kOhm. All parameters are known, all that remains is to calculate the resistance of the ammeter (indicator) shunt.

We will calculate the shunt for the ammeter using the following formulas:

Rsh=Rram * Iind / Imax; we get Rsh = 0.04 Ohm.

The main requirement for shunts is their ability to pass currents that do not cause excessive heating, i.e. have standards for electric current density for conductors. Various materials are used as shunts. Since I don't have any "different material" on hand, I'll use good old copper conductor.

Next, based on the fact that Rsh = 0.04 Ohm, using the reference book of resistivities of copper conductors, we select the appropriate size of a piece of copper wire. The larger the diameter, the better, but this increases the length of the copper wire. I will ignore these requirements and choose a meter segment. The main thing for me is that my shunt does not melt, especially since I will not force it above 6A. I twist the selected copper conductor into a spiral and solder it parallel to the measuring head. That's it, the shunt is ready. Now all that remains is to more accurately adjust the shunt resistance and calibrate the meter scale. This is done experimentally.

Actually, devices. Vidon is not very good, so what...

The other day I was reminded of another idea for computer modding. We will talk about how to connect a fluorescent (VFD) indicator from Soviet tape recorder to the computer.

Once upon a time, a long time ago, I had a Mayak 240-S1 tape recorder. Due to obsolescence, the tape recorder was scrapped. All that was left of him of value was an electroluminescent indicator, which I had lying around collecting dust. Once upon a time, a couple of years ago, I already tried to install it on a computer, but it did not fit the design.

The indicator looks like this:

And today I will tell you how to connect this or a similar indicator to a computer.

So, let's start with the schematic diagram:

but we don’t need the entire scheme, we are only interested in part

As can be seen in the diagram, the indicator has dual power: bipolar ±15 volts and alternating 5 volts. But the indicator remains operational when powered by a bipolar voltage of ±12 volts and constant voltage+5 volts.

Let's connect XP1 as follows (designations according to the diagram):

1 - zero
2 - +5
3 - +12
4 - -12
5 - zero

To make it more convenient to connect, I took a non-working and half-soldered motherboard

and soldered the wires with reverse side ATX connector and connected the power supply.

Now that power is supplied to the indicator, you need to send some signal to it. I will use an mp3 player as a signal source.

The XP2 connection diagram is very simple (designations according to the diagram):

1 - left channel
2 - right channel
3 - Fe tape type indicator
4 - indicator of the PN noise reduction system
5 - Cr tape type indicator
6 - microphone on indicator
7 - speaker on indicator
8 - recording indicator

Taking out a connection cable from your supplies CD-ROM drive to sound card

And having removed the original connectors from it, I soldered one end to the indicator board, and soldered a 3.5mm jack to the second

In general, this gray cable is a very good help in such cases, because inside the insulation there is a shielded two-channel stranded wire and for many applications it is long enough. But, unfortunately, in lately, very often these cables are not shielded. But I got distracted, let’s continue.