نظام التحكم عن بعد بالامواج فوق الصوتية (Ultrasonic) .. كتاب التلفزيون الملون والعادي

19-14 Ultrasonic remote control system:

Ultrasound waves are generated with a frequency range between (34-54 kHz),
Each frequency represents a specific function of the device, such as turning on and off and controlling the volume up and down. Changing the channel and the amount of frequency depends on the design of the device. There are no fixed frequencies in circulation, but each manufacturer may have its own system.


Some devices that operate in this system contain only three ultrasonic frequencies. Such as turning on, turning off, and sound at a frequency of (2.38) kHz. And search for the highest channel (1.8 kHz) and the first channel (40 kHz).

There are other devices that can generate 14 different frequencies. Many other functions can be controlled such as direct channel tuning. These frequencies are generated electronically.

Generating ultrasonic waves mechanically:

The device that generates ultrasound waves is located in the small mobile device for remote control, and mechanical vibrations are generated that are converted into ultrasound waves, and the receiving device in the TV receives these ultrasonic signals and converts them into electrical signals that control the functions and controls of the device.

19-15 The device with mechanically vibrating cylindrical tubes:

In it, waves are generated from the vibration of cylindrical rods (19-20), and the vibration may come from the air column or from mechanical elements. Whatever the method of generating vibrations, its work is similar, and a microphone captures these waves. The vibrating tube method is manufactured by ZENITH and others. It consists of several aluminum tubes that vibrate longitudinally when a special hammer hits them, moving towards their axes. The length of each tube determines its resonance and vibration frequency. If the length of the tube is 6.4 cm, for example, it vibrates at a resonant frequency of 50 kilohertz. Vibration is damped inside the tube, and most of the vibration energy is stored inside the tube after the end of the hammer movement.

In the device there are three or four tubes of slightly different lengths, as shown in the figure. As for the moving part (the hammer), it is a steel cylinder weighing about (2.5 g).

It is located on one end of the tubes. When the pressure is pressed, the hammer is pushed by the force of a spring and knocks on the tubes, and the frequency difference between each tube and another is often about (1000 Hz). In order to dampen the vibration of the tube, immediately after performing its work, a piece of plastic spring moves and touches the vibrating tube, and this plastic piece moves away when the press is pressed to produce another vibration.

pickup microphone:

It is a crystal microphone composed of barium titanate. This material is cut in the form of a bar or a slice. It is placed between two conducting poles, and a variable voltage is generated in it according to the mechanical vibrations that it collides with. In the opposite way, if the two poles - and between them the crystal - are exposed to a changing voltage, then a mechanical vibration is generated in the crystal. This phenomenon is called piezo electric.

The figure shows the installation of a crystal microphone, consisting of two thin slices of crystal (Part A), and two silver electrodes. They have a small section that touches in part each side. In a place that does not affect the vibration, two thin metal pieces shall be fixed with cement plaster and used as electrical contacts, and to suspend the elements mechanically. An aluminum piece shall be added and a space of a quarter wavelength around it shall be added in the form of a letter (U) to reach the frequency response of the device as in Figure (B). And it makes the device so that it behaves as two tuned circuits connected to each other, and the ultrasonic frequency range of this device is from 37.75 kHz to 4125 kHz and converts it into electrical signals proportional to it. Figure (C) shows the internal structure of the microphone and contains the various elements. The horn is 1.5 cm long. It works to direct the vibrations to the aluminum piece, then the poles and the crystal element. The horn and the internal vacuum, which is estimated at a quarter of the ultrasound wavelength, ensures the device has good sensitivity and is sufficient to pick up the ultrasonic signal. Without aiming carefully, and within the specified distance inside the house, the reflections of the signal on the walls, ceiling and pieces of furniture are sufficient for the microphone receiver to sense them and control the keys and controls of the television set, and the maximum distance within which the transmitter and receiver operate is not more than 12.2 meters.