Pontifícia Universidade Católica de São Paulo

Transcription

1 WIRELESS DATA TRANSMISSION Lesson Plan Author: Prof. Orivaldo Gonçalves de Mello (E.E. Pe Simon Switzar) Students from 11th and 12th grades from E.E. Pe Simon Switzar Raphaela Rodrigues Tatiane Aparecida Dantas de Brito Ricardo Guedes de Oliveira Supervision Prof. Marisa Almeida Cavalcante (PUC/SP) e Prof. Cristiane Rodrigues Caetano Tavolaro (PUC/SP) July 2009

2 Introduction It is important to recognize that the pupils have the intention to learn, but perhaps not what the school currently intends to teach them. That is, the education project many times has little to see with the learning project. Thus, what Physics must search in high school is to assure that the inquiry ability rescues the inquiry spirit, the desire to know the world we inhabit. Not only in a pragmatic way, as immediate application, but expanding the understanding of the world, in order to consider new questions and, perhaps, to find solutions. In teaching Physics questioning must be stimulated and not only giving answers to ideal situations. Physics also must be understood as culture, in a way that the school has the duty to assure the access of the population to part of the knowledge produced. It is not about, however, to abandon the contents or to go for generalities; the contents must be explored with severity, but they must go though criteria based choices and adjusted didactic treatment, so that it is not a lot of formulas and disarticulated information. History alone is not enough, as it is necessary to go beyond the process and understand it, to guarantee the inquiry. Far from meaningless empty slighted knowledge, it is needed to teach how things work. It is in this perspective that we consider this activity where specific content related to the electricity and Modern Physics will be approached, in order to understand a little more How things work. Through a very simple electric circuit it will be possible to understand the principle behind wireless communication systems what it will allow the pupils a contact with specific contents of electricity, but applied to devices present in their daily life, such as the technology involved in the use of remote controls, infra-red alarms, optical fiber cables, amongst others. The whole activity was articulated in order to make possible to develop abilities and skills as:

3 To understand that tables, graphs and mathematical expressions can be different forms of representation of the same relationship, with potentialities and limitations, to be capable to choose and make use of the most appropriate language in each situation, and being able to translate between themselves the meanings of these many languages. To elaborate analytical reports presenting and discussing data and results, either through experiments or critical evaluation of situations, using, whenever necessary, of appropriate Physics language. control. Objective To show pupils the principle of wireless transmission through a remote Content The content approached in this activity makes it possible to treat the following structured topics: Sound, image and communication treated in 11 th grade Rooster and Structured Topicss This activity can be explored in either 11 th or 12 th grade, depending only on the questions that you wish to answer. Structured topic 4: Sound, image and information (11 th grade) To place ourselves in the contemporary world it is necessary to understand the current means of communication and information, that has in its base the production of images and sound, processes of capture, codifications and forms of register and the

4 reestablishment of its signals in the receivers. To study these mechanisms means to propitiate abilities to understand, to interpret and to deal appropriately with technological apparatuses, as the television, CDs and DVDs players, the computer, the cinema or photography. Structured topic 3: Electromagnetic equipment and Telecommunications (12 th grade) Most devices and equipment that are part of our daily life require electric energy for its functioning, allowing the execution of different functions as to illuminate, to heat, to cool, to centrifuge, to triturate, to emit sounds and images, and so on. Moreover, a significant part of the available information nowadays circulates the planet through electromagnetic waves, and it does not need a medium for its transmission. Which processes and phenomena occur inside the devices so that the same electric energy provides many different effects? How radios and televisions transmit information? The understanding of the electromagnetic world that is in our daily life is indispensable to allow the adjusted, efficient and safe use of devices and equipment, beyond conditions to analyze, to make choices and to improve its use. Activity Number of classes needed for the activity: 4 classes First class -To explain the objective of the experiment, its relation to the daily life; The remote control is a device of ordinary usage in our daily life, therefore we are going to demonstrate that each key has a different frequency, and this varies from

5 one brand to another. We are going to use a reception system for this demonstration that consists of a phototransistor connected to the sound board of the computer, where the reading is made through Audacity Software. Materiais ued for its functioning a) Remote control. Its function is send infra red signals to the phototransistor. Fig.1: Remote controls b) Phototransistor. Its function is to convert the infra red signals in electric signals that will be sent to the computer s sound board. Fig. 02: Phototransistor

6 c) Support with a 470 ohms resistor. The resistor detects electric current variations and the Potential difference in its terminals. d) Cables in which one of their ends has two alligator clips and on the other end an audio Jack mono connector. The alligators connected to the terminals of the 470 ohms resistor make the connection to the PC (In the sound board port). e) 9 - volt batteries. Experiment s main power source. Fig.03: resistance in series with a LED, battery and phototransistor. Signal being captured by the alligator clips in parallel with the resistance. (pink). f) The connector for the classmate PC must be connected to the mic port g) LED to indicate the functioning of the circuit. Fig. 04: jack connector connected to the mic port of the classmate PC.

7 h) Audacity software, available on the Internet and essential to analyze the signals sent by the remote control. ( Fig. 05 shows an example of signal observed from pushing a key of a remote control in front of the phototransistor of the circuit of fig.02 and 03. Fig. 05: Audacity screen.

8 transmission. Figure 6 shows the complete equipment to make the reading of the wireless Fig. 06: Complete overview of all the utilized components. Instructions to turn on the components: The electrical resistance, the LED, the phototransistor and the battery must be connected in series, constituting the receiving system. Figure 07 shows the electric circuit s diagram. phototransistor battery resistance LED Fig. 07: Diagram of the electric circuit of the receiving system.

9 Important!!! Hint about polarity: Both the LED and the phototransistor must be connected respecting the polarity for their conduction. To verify if this polarity is being respected follow these procedures: 2. If it turns on its polarity is correct. If it does not turn on change the polarity of the battery and keep at least one of the polar regions connected not to lose reference. 1. Connect only the LED in the circuit of fig.07, removing the phototransistor and verify if the LED turns on. 2. If it turns on its polarity is correct. If it does not turn on change the polarity of the battery and keep at least one of the polar regions connected not to lose reference. 3. After that connect the phototransistor and shed a beam of light on it (a lantern or a laser tip) and see if the LED turns on. 4. If it turns on the polarity of the phototransistor is correct. 5. If it does not turn on invert the phototransistor s polarity (do not move the battery as the polarity of the LED must also be respected). 6. After that put the remote control in front of the Phototransistor and press any key. Observe the LED. It will blink with the frequency of the remote control. Capturing the signal a. With the circuit mounted place an alligator beside the resistor and the other on the opposite side (so that the two are parallel to the electrical resistance). b. Connect the exit of the alligators to the computer s sound board. c. Do the reading on the Audacity software (Reading of time in seconds).

10 Second Class Do the experiment. a. Put the equipment together and start the Audacity software, pressing the program s record button, leaving the time in seconds. Fig. 08: changing Audacity s configuration so it is possible to measure time in seconds

11 b. Press a key of the remote control in front of the phototransistor. Fig. 9: Remote control being used in front of the transistor c. Observe the graph that the software received from the remote control. Amplify the signal by clicking on the software s magnifying glass. Fig.10: an example of measurements taken of the time interval of each signal parcel. d. To measure put the cursor over the signal and select the time interval correspondent to a period of wave. e. Write down each time interval that you feel is important and also calculate the frequency of each remote control. f. Export the archives as wav file in the Audacity so that it is possible to read it in any machine. Give each file a name key_remote control (for example key

12 1_control Sanyo DVD), thus it will be possible to easily locate the measurement done for posterior analysis. g. Repeat this procedure for different remote controls. Third Class From the time in seconds that the software has measured you will be able to calculate and analyze the frequency of each, as f = 1/T. Examples of graphs showing signal emitted: Fig.11: Universal Control - Power code ( Fig.12: Universal Control - Power signal showing the period of wave (

13 Fig. 13: LG Control - Power code ( Fig. 14: LG Control - Power signal showing the period of wave ( Fig. 15: Sanyo Control - Power code (

14 Fig. 16: Sanyo Control - Power signal showing the period of wave ( Fourth Class Analyze the results To analyze the results the teacher should ask students to compare: 1. Signals from different keys in the same control 2. Same key from different remote controls. Students have to answer the following questions: For the same remote control and different keys: a. What happens with the signal frequency? Is it the same? Does it change from key to key? b. What happens to the length of the signal? Is it the same or does it change from key to key? c. What happens to the maximum and minimum sequence (logical sequence)? Does it change?

15 For the same key from different remote controls: a. What happens with the signal frequency? Is it the same? Does it change from remote control to remote control? b. What happens to the length of the signal? Is it the same or does it change from remote control to remote control c. What happens to the maximum and minimum sequence (logical sequence)? Does it change? According to your experimental observations could you answer why a specific remote control only works on the device it has been planned for? Links Videos that show the equipment being put together Text about analogical digital signal conversion Cavalcante, M.A; Bonizzia, A.,Gomes,L.C.P; Data acquisition in the physics laboratory: an easy, simple and low-cost method for experiments in mechanics, Rev. Bras. Ensino Fís. vol.30 no.2, São Paulo, 2008