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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Hand movement control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer Before describing the proposed design, an important note should be made. The developed contactless control element can be used not only in computer technology. The described design and purpose of the device is just one example of its possible applications. Among fans of aviation history, the computer game “IL-2. Forgotten Battles” with its numerous additions is deservedly popular. Not a single history textbook can explain the calm courage of an attack aircraft pilot, carefully and accurately, as in a laboratory experiment, leading a machine tormented by anti-aircraft guns on a combat course. Or the frantic excitement of the Raiden pilot, seeing the silhouette of the Boysan growing in his sights. However, the position of the virtual pilot is not as comfortable as that of a real one. And the picture on the monitor is inferior to reality, and there simply aren’t enough hands to operate the keyboard. The last problem is partly solved using a joystick. Here there would be more pedals to control the steering wheel. However, they are only available in very rare and expensive devices. True, even in cheap models there is a third regulator that can be used as desired: either as pedals or a gas sector. Having opened my joystick (Fig. 1), I discovered that the extreme terminals of all its variable resistors (potentiometers) are connected in parallel. Obviously, one or another constant voltage is removed from them, which is supplied to the circuit. This was the starting point for development. The simplest solution is obvious - to make pedals whose axis will be a variable resistor. They can complement the simulated control system of any real aircraft. But, in addition to high technical and historical reliability, such a solution also has considerable disadvantages. The design is very bulky and heavy. There is a problem with attaching it to the floor. At the hottest moment of a battle, or when it is necessary to keep such a “beast” as the La-5FN from turning around due to the reactive torque of a powerful engine, it is difficult to resist not pressing the pedal properly. Backlash in mechanical components makes control difficult. The wear and tear of variable resistors does not bring joy either. In a word, some other design is required, albeit not so historical, but more convenient and compact. Why don’t we “furnish” all these mice, keyboards, touch screens of iPhones, which certainly require direct contact, and tear the control process away from the surface of the panel, transfer it to the volume above it? Remember how in one of the stories by Kir Bulychev: “The alien passed his palm over the green light. It went out and lit up again brighter than before.” We can do this too. The first thing that comes to mind when thinking about contactless control is optics. However, most optical systems operate on transmission or beam interruption. Insert your hand into some gap between the light source and the receiver? Who needs such a “contactless” device? Reflective circuits usually deal with special, contrast-printed marks and barcodes. At the same time, the reliability of their reaction to an object, which can be of any color and texture, is also questionable. Another circumstance limits the freedom of choice of the designer - the best optics use lasers. But their radiation is harmful to vision and therefore it is undesirable to use them in control panels that a person looks at. The inevitable contamination and dusting of optics during operation also creates problems from time to time. Finally, if there is more than one sensor, this leads to a significant complication and increase in cost of the circuit. Therefore, I decided to go the route of using capacitive sensors. The first such systems used oscillatory circuits and were very unstable. Almost every time they were turned on, they needed to be adjusted. Later, more stable digital designs based on the principle of pulse delay appeared. However, these were ordinary touch devices. Their authors, apparently, did not have enough imagination to imagine a device that worked without direct touch. I decided to try... Take a look at Figure 1. The generator on elements D1.2, D1.1 produces pulses to the pulse shaper along the edge at D 1.3, D 1.4. At its output (pin 11) there is a logical 1 all the time, except for the moment after the arrival of the pulse front from the generator output (pin 3). During the delay time of the pulse in the chain R4, R3, CA, logical 1.4 is set at all inputs of D1, and logical 0 is set at the output. While the capacitance of the CA sensor, and therefore the duration of the zero pulse, is small, the averaged constant voltage at the output of the shaper is smoothed R6, C3 is practically no different from a logical unit. But as soon as the sensor capacity increases, logical 0 at the output of the driver takes up most of the clock pulse period and the output voltage decreases. To obtain the proper sensitivity of the device, it is necessary that the duration of the shaper pulses be comparable to the period of the clock pulses (but not exceed them). This is achievable at clock generator frequencies of at least 100 kHz.
Now let's look at the design of the capacitive sensor (Fig. 2). It is a horizontally located plate of foil fiberglass. The second (ground) covering is a tin casing-screen, in which the device board is placed vertically. They form a somewhat unusual, semi-open capacitor with the plates arranged perpendicular to each other. It clearly reacts by increasing its capacity to the placement of any object, both conductive and dielectric, in its field. The object is felt at a distance of at least 30 mm. This design gives a fairly wide signal that can overcome various interferences and instabilities. And the operational amplifier DA1 can bring its amplitude to any required value. Bring your foot closer to the plate and the rudder of your plane will turn. Move your leg back up or back and the process is reversed.
There are two capacitive sensors, like pedals in a real airplane. Since the signal from one sensor is connected to the inverting input of the amplifier, and from the other - to the non-inverting input, the output voltage depends on their balance, on which leg you “give” more. At the same time, the circuit is not very complicated, because both the clock generator and even the D1.3 inverter can be common to several channels. Amplification of the op-amp by several orders of magnitude for smooth regulation is clearly redundant. You can change the “gear ratio” of the control by introducing a negative feedback circuit. R9 reduces the gain, and in alternating current the feedback is even deeper, thanks to capacitor C 5. This eliminates the possibility of self-oscillations. The printed circuit board of the device is shown in Figure 3. In areas of the board free of foil in the area where capacitive sensors are connected, many holes with a diameter of about 3 mm are drilled to reduce the initial capacitance and increase the sensitivity of the device. The inputs of unused D2 elements are grounded to avoid damage by static charges. It is advisable to make these conductors thin. Then, if necessary (failure of working elements or some modifications), you will be able to cut them and use these elements.
Design. The plates of capacitive sensors are located with the foil facing up. They are hinged and can be lifted and pressed against the walls of the case, forming a compact box, convenient for carrying and storage. For this purpose, in the area of the cutouts, axles are soldered from scraps of copper wire with a diameter of 0,8 mm. Also soldered to the plates are flexible wires to the circuit (preferably MGTF) and wire rings that hold the unstripped part of them and prevent the wire from breaking at the stripping site. After all soldering has been completed, the working surface of the sensor must be insulated from electrical contact with foreign objects. In many cases, a stick of wide adhesive tape is sufficient for this. The body of the device is a U-shaped plastic frame 2 mm thick. From scraps of plastic, guides for the board and bosses are cut out and glued from the inside, in which threaded holes are made for attaching the screen casing. The sensor plates are inserted into the cuts in the lower legs of the case with their axes and sealed with overlays that also secure the lower part of the board. The U-shaped casing-screen is made of tin. To reduce the initial capacity and the influence of the supporting surface, it does not reach the bottom of the case a few millimeters. A hole is made in the screen opposite the tuning resistor R4. From the inside, a flexible wire is soldered to the screen to connect to the common wire of the board.
Establishment. Set R4 to middle position. Instead of RЗ, solder an adjusted resistor with a resistance of about 1 MOhm on short wires. Set it to the minimum value. Make sure that the trimmer, its wires and any other objects do not fall into the field of the CA sensor. Smoothly increase its resistance until the constant voltage at pin 11 of DD1 decreases by 20 - 25%. This is a signal that the device has begun to sense the surrounding space. Measure the resistance of the trimmer and replace it with the same constant resistor, and move the trimmer to the place of R5 so that it does not fall into the field of the SB sensor. Set the output of the second driver to the same voltage as the output of the first. Set the final balance with resistor R4 using a thin dielectric screwdriver after complete assembly of the device. Take out the screwdriver and check the voltage at the output of the op-amp - it should be close to half the supply voltage. The device was successfully tested with the IL-2 programs and the Condor airframe simulator. The degree of realism turned out to be very close to a real aircraft. However, the mentioned programs are not created for wingless people. Look at the Pioneer ball and, after a little training, everything will be fine. As already mentioned, the proposed contactless control element can be used not only in computer technology. In most cases there is no need for a two-channel balanced circuit such as the one described. A single channel element can be made as shown in Figure 5.
Since the output of the shaper is connected to the inverting input of the op-amp, in the initial state the voltage at the output of the device is low. The voltage at the non-inverting input is set by trimmer R10 just below the switching threshold. If you bring your hand to a capacitive sensor, the voltage at the device’s output will begin to increase. It can be used to regulate or simply turn on and off any devices. In the latter case, an OOS circuit is not required. During experiments with the device, this option proved to be quite workable. When integrating contactless control into any equipment, you should remember that the sensor responds to the capacity introduced by objects not only in front, but also behind it, that is, in the equipment body. It is important that this parasitic capacitance be smaller, and most importantly, unchanged. A loose sensor mount or wires dangling loosely next to it can confuse the settings. This will not allow for good sensitivity. It is interesting to use contactless control (two independent channels) for the movement of any doors, sashes, etc. By installing two sensors on the handle, as shown in Figure 6, you can “push” the sash to any desired position without touching it.
Of course, classic toggle switches and regulators are simpler and cheaper. But there are still areas of application where the proposed non-contact control elements will be more preferable. For example, in hazardous working conditions, when it is necessary to completely eliminate electrical contact with equipment, transmission of infection, etc. Thus, many devices in the future will be able to be controlled with literally one wave of a hand not armed with remote controls, tokens or any other devices. Author: A.Lisov
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