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Ultrasonic Communicator (ART475E)

In one of his histories, Professor Ventura describes the use of a transmitter and an ultrasonic receiver to send responses of a test by unconventional means. Showing that it is possible we give the complete design of the system for telegraphic signals.

We can transmit sound telegraphs imperceptibly using ultrasound, as we described in Professor Ventura's story available on the website in the corresponding section. With it, students send the answers of a test through ultrasound, being the signals received by a special receiver.

Well, we describe in this article the assembly of both the transmitter and the receiver, hoping that readers will use the system for didactic purposes or in trade shows, not in the original application of the story ...

The transmitter consists of an oscillator with 555 that is set to operate at a frequency between 18,000 and 22,000 Hz, which can be reproduced in good yield by a small piezoelectric tweeter. A power transistor feeds the tweeter, making it possible to emit a few tens of meters.

This transmitter is powered by 4 common batteries and has its circuit shown in figure 1.

 

Figure 1 - The transmitter diagram
Figure 1 - The transmitter diagram

 

The assembly may be made on a printed circuit board as shown in Figure 2.

 

Figure 2 - Printed circuit board for mounting
Figure 2 - Printed circuit board for mounting

 

When mounting the transmitter, note the position of the integrated circuit and transistor, which should have a small heat sink. The manipulator can be improvised with metal plaques or a pressure switch can be used.

The resistors are 1/8 W with any tolerance and the electrolytic has a working voltage of 6 V or more. The receiver uses a small piezoelectric tweeter as a microphone (sensor) applying its signal to an amplifier transistor that excites a frequency divider with the 4017.

Dividing the frequency of the captured ultrasound it converts to sound and with that, when applied to a transistor, it can be heard on a small speaker or headset. In figure 3 we have the complete diagram of the receiver.

 

Figure 3- Receiver diagram
Figure 3- Receiver diagram

 

The assembly can be done on a small printed circuit board as shown in figure 4.

 

Figure 4 - Printed circuit board for mounting
Figure 4 - Printed circuit board for mounting

 

On assembly, note the position of the integrated circuit and transistors, as well as the polarity of the electrolytic capacitor. The resistors are 1/8W with any tolerance and the tweeter as a microphone must have the internal transformer removed so as to connect only the high impedance transducer to the circuit.

To test and use, turn on the transmitter, press the handler and adjust P1 so that the sound becomes very sharp and then disappears in the ultrasound range. Place the receiver in front of the transmitter and set P1.

The sound of the transmitter must be heard.

 

a) Transmitter

CI-1 - 555 - integrated circuit

Q1 - BD135 - medium power NPN transistor

S1 - Manipulator

B1 - 6 V - 4 small battery

TW- piezoelectric tweeter

P1 - 100 k ohm - trimpot

C1 - 10 nF - ceramic or polyester capacitor

C2 - 10 uF - electrolytic capacitor

R1 - 10 k ohm - resistor - brown, black, orange

R2, R3 - 1k ohm - resistors - brown, black, red

 

Several:

Printed circuit board, battery holder, mounting box, wires, solder, etc.

 

b) Receiver

CI-1 - 4017 - integrated circuit

Q1 - BC548 - NPN general purpose transistor

Q2 - BD135 - medium power NPN transistor

TW-piezoelectric tweeter - see text

S1 – On/Off switch

B1 - 6 V - 4 small batteries

P1 - 100 k ohm - trimpot

C1 - 100 uF - electrolytic capacitor

R1 - 1 M ohm - resistor - brown, black, green

R2 - 10 k ohm - resistor - brown, black, orange

R3 - 1k ohm - brown, black, red

 

Several:

Printed circuit board, battery holder, wires, solder, etc.