Electronic Process Internship Report

One: Internship purpose

1.Familiar with the use of common tools for manual welding and its maintenance and repair

2. Basically master the welding technology of manual soldering iron, which can complete the installation and welding of simple electronic products independently. Familiar with the production process of the installation process of electronic products.

3. Familiar with the design steps and methods of printed circuit boards, familiar with the process flow of hand-made printed circuit boards, and can design and manufacture printed circuit boards according to circuit schematics and components.

4. Familiar with the categories, symbols, specifications, performance and scope of use of commonly used electronic components, and can refer to related electronic device books.

5. Ability to correctly identify and select commonly used electronic devices, and be proficient in using ordinary multimeters and digital multimeters.

6. Understand the welding, debugging and maintenance methods of electronic products.

Two: Internship requirements

1. Students are required to be familiar with the identification and testing methods of commonly used electronic components.

2. Ask students to practice and master the correct welding method.

3. Require students to practice and master the basic requirements of electronic technology, understand the process files of electronic product production, compare the schematic diagrams of the electronic products, understand the wiring diagrams, understand the symbols and legends on the drawings and compare them with the physical objects.

4. Carefully read the relevant technical drawings and files, and carefully install them separately, weld them, and record relevant experiences, experiences and experiences.

5. According to the file debugging, the instrument and the machine will be used to debug the movement, learn to eliminate the fault, and make the whole machine meet the index requirements.

6. According to the guidance of the process file, independently package the whole casing to complete a formal product.

Three: Internship tools and components

Internship tool

Electric soldering iron: horseshoe shape, high power 35 watts, tweezers, solder rosin, two sections, 5th battery

element

Resistor: 11 resistors of various colors

Identification and detection of resistance: The resistance is represented by a "r" plus a number in the circuit. For example, r1 represents a resistor numbered 1. The main role of the resistor in the circuit is shunt, current limit, voltage division, offset, and so on. There are three kinds of parameter labeling methods for resistance, namely, direct label method, color scale method and number label method. a, the number standard method is mainly used for small-volume circuits such as patches, such as: 472 means 47 × 100ω; 104 means 100kb, color ring labeling method is the most used, the examples are as follows: four-color ring resistance five-color ring resistance 2, resistance The relationship between the color mark position and the magnification is shown in the following table: Color Effective Digital Magnification Allowable Deviation Silver / x0.01 ±10 Gold / x0.1 ±5 Black 0 +0 / Brown 1 x10 ±1 Red 2 x100 ±2 Orange 3 x1000 / Yellow 4 x10000 / Green 5 x100000 ±0.5 Blue 6 x1000000 ±0.2 Purple 7 x10000000 ±0.1 Gray 8 x100000000 / White 9 x1000000000 /

Capacitance: Ceramic Capacitor 1p: 1 2p: 2 5p: 2 15p: 1 30p: 2 47p: 1 120p: 1 102: 2 103: 4 223: 1 473: 1 104 :6

Electrolytic capacitor: 4·7uf: 2 10uf: 3 47uf: 1 220uf: 2

Capacitance identification and detection: Capacitors are generally represented by "c" plus numbers in the circuit. The capacitor is an element consisting of two metal films abutting and separated by an insulating material. The characteristics of the capacitor are mainly DC-DC communication.

The size of the capacitor capacity is the size of the energy that can be stored. The blocking effect of the capacitor on the AC signal is called capacitive reactance, which is related to the frequency and capacitance of the AC signal.

Capacitance xc=1/2πf c

Common types of capacitors used in telephones are electrolytic capacitors, ceramic capacitors, chip capacitors, monolithic capacitors, tantalum capacitors, and polyester capacitors.

2. Identification method: The identification method of the capacitance is basically the same as the identification method of the resistance, and there are three types: the direct label method, the color scale method and the number standard method. The basic unit of the capacitor is expressed in terms of pull, and other units are: millifarad, microfarad, nanofarad, and picofarad.

Where: 1 Farad = 103 millifarads = 106 microfarads = 109 nanofarads = 1012 picofarads

The capacity of a large capacity capacitor is directly indicated on the capacitor, such as 10 uf/16v

Capacitance values ​​of small capacitances are represented by letters or numbers on the capacitors.

Letter notation: 1m=1000 uf 1p2=1.2pf 1n=1000pf

Digital notation: Generally, three-digit numbers are used to indicate the capacity. The first two digits represent significant digits and the third digit is magnification.

For example, 102 means 10×102pf=1000pf 224 means 22×104pf=0.22 uf

Diode: in4001:1

The identification and detection method of the diode: the main characteristic of the diode is unidirectional conductivity, that is, the on-resistance is small under the action of the forward voltage; and the on-resistance is extremely large or infinite under the action of the reverse voltage. Identification method: the identification of the diode is very simple. The n-pole of the low-power diode is mostly marked by a color circle on the external surface of the diode. Some diodes also use the special symbol of the diode to represent the p-pole or n. Extremely, there are also test notes that use the symbol marks "p" and "n" to determine the polarity of the diode: when using a digital multimeter to measure the diode, the red pen is connected to the positive pole of the diode, and the black pen is connected. The negative pole of the diode, the resistance measured at this time is the forward conduction resistance of the diode, which is the opposite of the pointer connection of the pointer multimeter.

Triode: 9018h: 1 9014c: 1

Triode identification and detection method: The triode has three pins. The known type and the pin arrangement of the triode can be judged by the following methods.
? Measure the resistance between the poles. Place the multimeter in r × 100 or r × 1k, and test according to the six different methods of red and black. Among them, the forward resistance values ​​of the emitter junction and the collector junction are relatively low, and the resistance values ​​measured by the other four connections are high, about several hundred kilohms to infinity. However, whether it is low resistance or high resistance, the inter-electrode resistance of the triode of the material is much larger than the inter-electrode resistance of the material triode. b? detection discriminating electrode
? Determine the base. Use the multimeter r × 100 or r × 1k block to measure the positive and negative resistance values ​​between each of the three electrodes of the triode. When the first pen is connected to one electrode and the second pen touches the other two electrodes to measure the low resistance value, the electrode to which the first test pen is connected is the base b. At this time, pay attention to the polarity of the multimeter pen, if the red pen is connected to the base b. When the black test pens are connected to the other two poles, the measured resistance values ​​are small, then the measured triode body is a pnp-type tube; if the black meter pen is connected to the base b, the red test pen contacts the other two poles respectively. When the measured resistance is small, the measured triode is an npn-type tube.

? Determine the collector c and the emitter e. When the multimeter is placed in the r×100 or r×1k block, the red test pen base b is used, and when the black test pen is used to contact the other two pins, the measured two resistance values ​​will be larger, a smaller one. . In the first measurement with small resistance, the pin connected to the black test pen is the collector; in the first measurement with large resistance, the pin connected to the black test pen is the emitter.

Other components used are: air-core coils

Four: Working principle and content

working principle

1. Radio Broadcasting Basics: A broadcasting station broadcasts a program by first converting the sound into an audio electric signal through a microphone, and is amplified by a high-frequency signal. At this time, a certain parameter of the high-frequency carrier signal changes correspondingly with the audio signal. The audio signal to be transmitted is included in the high-frequency carrier signal, and the high-frequency signal is amplified, and then the high-frequency current flows through the antenna to form a radio wave to be emitted outward, and the radio wave propagation speed is 3×108 m/s. The radio wave is received by the radio antenna, then amplified, demodulated, restored to an audio electrical signal, sent into the voice coil of the speaker, causing the corresponding vibration of the paper cone, the sound can be restored, that is, the sound and electricity conversion transmission - electricity The process of acoustic conversion. The frequency of the medium wave is specified as 525-1605khz. The shortwave frequency range is 3500-18000khz

2. Radio Broadcasting and Receiving Process: The transmission of a broadcast program is performed on a radio station. The sound wave of the broadcast program is converted into an audio electric signal by the electro-acoustic device, and amplified by an audio amplifier, and the oscillator generates a high-frequency equal-amplitude oscillating signal modulator to modulate the high-frequency equal-amplitude oscillating signal by the audio signal; the modulated high-frequency The oscillating signal is amplified and sent to the transmitting squall line, which is converted into radio wave radiation. The reception of radio broadcasts is done by radio. The receiving line of the radio receives the electric wave in the air; the tuning circuit selects the signal of the desired frequency; the detector restores the high frequency signal into an audio signal; the demodulated audio signal is amplified to obtain sufficient driving power; Electroacoustic conversion restores the broadcast content.

3. The working principle and process of radio frequency modulation system and amplitude modulation system

AM radio: used to receive AM broadcast programs. The demodulation process uses a detector to demodulate the amplitude modulated high frequency signal. The circuit structure is shown in the figure. AM radios generally work in medium, short or long wave bands

FM radio: used to receive FM radio programs. The demodulation process uses a frequency discriminator to demodulate the frequency modulated high frequency signal. In the transmission process, the amplitude of the FM signal is fluctuated due to various interferences. In order to eliminate the influence of the interference, the limiter is often used to limit the amplitude of the frequency modulation signal before the frequency discriminator, so that the frequency modulation signal is restored to the equal amplitude state, and the circuit structure is shown in the figure. FM radio generally works in the ultra-short wave band, and its anti-interference ability is strong, the noise is small, the audio frequency is wide, and the sound quality is better than the AM radio. High-fidelity radios and stereo radios are FM radios. The FM bands are in the UHF band, and the international regulations are 87-108b.

4·edt—2901 radio circuit principle

Am`fm switch is composed of q2`q3`r5~r8`c7 frequency modulation and amplitude conversion circuit. After the power switch sw3 is switched to the on state, the q2 is turned on, q3 is turned off, and the a/f is connected to the output high level. Connect to the motherboard a/f connection 埠, one way through r107 to u1's 15 feet, 15 feet high level 1c automatically switch to the FM band.

The FM high-frequency signal received from the whip antenna is amplified by c101 to q101, and the band-pass filter composed of components such as c104`l101`c106 is selected, and the FM signal of fm is sent to the 12-pin of u1, and the FM signal of 12-pin of u1 The internal frequency selective amplifier and the peripheral pvc`c109`l103 form a frequency selective channel frequency selective amplification, the local oscillator circuit composed of pvc`c110`l104, etc., the local oscillator signal is input from the 7-pin, and is sent together with the frequency-modulated frequency-selected signal. U1 internal mixing circuit mixing to get 10.7mhz FM IF signal output from 14 feet. The 10.7mhz IF signal is sent to the cf2 ceramic filter via r109, and most of the clutter outside the 10.7mhz wideband is filtered out. The 10.7nhz IF signal is input from the 17th pin of u1 and the 1c internal IF is amplified. The frequency-corrected audio signal is output from pin 23 of u1. The other frequency of the local oscillator is sent to the display driver sc3610. The 35th pin input 1c internally wakes up and the frequency is accurately displayed on the screen.

Press sw7, q2 cuts q3 to turn on u1, pin 15 is low level, u1 internally switches to amplitude modulation band, and when medium wave `short wave switch is to mw, the high frequency amplitude modulated medium wave signal sensed by the magnetic bar antenna Pvc frequency selection, converted by the band switch sw1 into the 10 feet of u1. The medium wave band local oscillator circuit is composed of t101`pvc and other components. The 5-pin local oscillator signal of u1 and the 10-pin frequency selective signal are simultaneously applied to the internal mixer, and the mixing frequency is 455khz amplitude-modulated intermediate frequency signal, 455khz intermediate frequency. The signal is output from pin 14. Push the short-wave switch to select the short-wave 1~8 band. The short-wave high-frequency signal received from the whip antenna is amplified by c101 to q101. The c102 is coupled to the medium-short-wave switch sw1 band switch to convert from the u1 pin 10 input. The short-wavelength circuit of short-wave 1~8 consists of components such as t102`t103`pvc`c112`c113. The local oscillator signal is input from the 5-pin by the band switch sw1, and is sent to the mixer for mixing with the short-wave high-frequency signal of the 10-pin. The intermediate frequency signal of 455khz is output from the 4-pin. The amplitude-modulated IF signal of the 14-pin output is frequency-selected by r106`t104`cf1. After filtering out most of the clutter except 455khz wide-band, it is sent to the 16-pin input of u1. The IF signal is amplified inside 1c and detected. The audio signal is output by pin 23. The AM local oscillator signal is sent to the display driver sc3610 through the c114 pin input to the inside for processing, and the processed frequency number is accurately displayed on the screen.

The audio signal output from the 23 pin of u1 is input from the 24 pin via c123 coupling, and w1 is the electronic volume control potentiometer, which controls the level of the 4th pin of u1 to control the volume. The audio signal output from the 23 pin of u1 is sent to the 24 pin of u1 via c123, such as 1c internal power amplifier, and the amplified audio signal is driven from the 27 pin to push the speaker or earphone.

The clock control and drive display circuit are composed of liquid crystal display, sc3610, x1, c1~c6, r1~r5`sw1~sw8`q1, etc. The 1~16 pins of sc3610 are the display drive output, and the 17 and 18 feet are the oscillation input. , output, 23, 24 feet adjustment time control, 26 feet is clock, frequency mode conversion, 27 feet for timing switch output, 32 feet am / fm selection control, 33 feet for amrf input, 35 feet for fmrf input, 36 feet Positive power supply.

Five: debugging

Fm band prompt: the first step, adjust the receiving frequency range, connect the power supply, press the fm button, work in the fm state, adjust the quadruple variable capacitor to the lowest end, the display shows the fm frequency, and adjust the l104 oscillation coil with a screwdriver. The digital display shows about 59mhz, and adjusts the quadruple variable capacitance to the highest end of the frequency display. Use the driver to adjust the variable capacitor on the top of the oscillation to connect the fine-tuning capacitor f/o so that the number on the display is displayed at about 108.5mhz. Repeat the above adjustment to make the fm frequency. In the range of 59~108.5mhz. The second step, adjust the sensitivity, adjust the quadruple capacitor to about 70mhz, receive a radio to adjust l103 to make the speaker output the loudest, then adjust the quadruple variable capacitor to display 106mhz to receive a radio, adjust the quadruple variable capacitor Another trimming capacitor f/a makes the speaker output the loudest. Repeat the above adjustment to achieve the best sensitivity, and seal the coil with wax.

Short adjustment of the medium wave: the first step, adjust the receiving frequency range, connect the power supply, press the am button, work in the am state, push the am band switch to the mw position, turn the quadruple variable capacitor to the lowest end, and the display shows Am frequency, use the screwdriver to adjust the t101 medium wave oscillation so that the digital display is around 515khz, adjust the quadruple variable capacitance to the highest end of the frequency display, and use the driver to adjust the variable capacitor to oscillate the fine-tuning capacitor a/o to make the number on the display Displayed around 1630khz, repeat the above adjustment mw frequency in the range of 15~1630khz, the second step, adjust the sensitivity, adjust the quadruple variable capacitance to about 600mhz, receive a radio to adjust the magnetic rod coil position to make the speaker output sound the loudest, then Adjust the quadruple variable capacitor to display a radio station around 1400mhz, adjust the quadruple variable capacitor mw and another trimmer capacitor a/a to maximize the speaker output. Repeating the above adjustments is the best sensitivity. The coil is sealed with wax.

Short-band adjustment: Short-band adjustment is relatively simple, short-wave uses a high-frequency amplifier circuit without adjusting sensitivity, as long as the frequency is adjusted. The frequency adjustment is also very simple. First adjust the medium wave and then push the band switch to sw1. The quadruple variable capacitor is adjusted to the lowest end. t102 The short-wave oscillation frequency is displayed at 3.8mhz, and the short-wave 1~5 is automatically synchronized. The switch is pushed to the sw8 position, and the t103 short-wave oscillation is adjusted to make the frequency appear around 17.9mhz, and the short-wave 6~8 is automatically synchronized.

Amif mid-week t104 adjustment: find a strong short-wave radio station, t104 to make the speaker output sound the most clearest.

Six: experience

In the one-week electronic process internship, the harvest was quite high. If we have learned some theoretical knowledge before, then this internship has let us experience a real practice. From the simplest identification of resistors and capacitors, as well as the identification, use and detection of various electronic components, to the correct use of soldering irons and proper soldering, the layout and fabrication of pcb boards are known. It is all we feel a sense of freshness, a strong desire for knowledge rises in our chest.

This internship is undoubtedly a good opportunity for us to exercise, so we have a more serious attitude from the beginning, whether it is from understanding the basics of radio broadcasting and its realization principle, or later welding for me. It is an improvement. The key task of this internship is welding. Since some simple boards have been soldered before, welding is not difficult for us, but due to the tight layout of electronic components, soldering should be handled with care. If the welding is wrong, it will take some effort to remove it, and it may not be able to take it down. Therefore, I dare not neglect. There was still a small problem during debugging, and the display was a bit unstable, but with the help of my classmates, I finally solved it perfectly.

This internship made me understand that in modern high-speed development, it is not enough to use only some theoretical knowledge to arm the brain. We also need to use practical hands-on ability to dress up our hands. Only then can we live up to the motherland. We cultivate, do the successor of the motherland, and contribute our own strength to the motherland.