Knowledge and skills required for qualified electronic engineers
I think that if you master the following hardware and software knowledge, you can basically become a qualified electronic engineer:
Part I: Hardware knowledge
I. Digital signal
1. TTL and buffered TTL signal
2. RS232 and definition
3. RS485/422 (balanced signal)
4. Dry contact signal
II. Analog signal video
1. Unbalanced signal
2. Balanced signal
III. Chip
1. Package
2. 7407
3. 7404
4. 7400
5. 74LS573
6. ULN2003
7. 74LS244
8. 74LS240 9. 74LS245
10.
74LS138/238
11. CPLD (EPM7128)
12. 1161
13. max691
14. max485/75176
15. mc1489
16. mc1488
17. ICL232/max232
18. 89C51
IV. Discrete devices
1. Package
2. Resistors: power consumption and capacitance
3. Capacitors
1) Monolithic capacitors
2) Ceramic capacitors
3) Electrolytic capacitors
4. Inductors
5. Power conversion module
6. Terminal blocks 7.
LED light-emitting tubes
8. 8-digit (common anode and common cathode)
9. Transistor 2N5551
10. Buzzer
V. MCU minimum system
1. MCU
2. Watchdog and power-on reset circuit
3. Crystal oscillator and ceramic capacitors
VI. Serial interface chip
1. EEPROM
2. Serial I/O interface chip
3. Serial AD, DA
4. Serial LED driver, max7129
VII. Power supply design
1. Switching power supply: device selection
2. Linear power supply:
1) Transformer
2) Bridge
3) Electrolytic capacitor
3. Power supply protection
1) Bridge protection
2) Single diode protection
VIII. Maintenance
1. Power supply
2. Watchdog
3. Signal
IX. Design ideas
1. Power supply: voltage and current
2. Interface: serial port, switch input, switch output
3. Switch signal output conditioning
1) TTL->Relay
2) TTL->Relay (reverse logic)
3) TTL->Solid state relay
4) TTL->LED (8-digit)
5) Relay->Relay
6) Relay->Solid state relay
4. Switch signal input conditioning
1) Dry contact->Optocoupler
2) TTL->Optocoupler
5. Consideration of CPU processing power
6. Consideration of becoming a product:
1) PCB appearance: size, shape, connector, space volume
2) PCB modular design
3) Cost analysis
4) Component redundancy
1. Power consumption of resistors
2. Withstand voltage of capacitors, etc.
5) Chassis
6) Power supply selection
7) Modular design
8) Cost accounting
1. How to calculate the cost of PCB?
2. How to reduce costs? Choose devices with functions that meet the requirements and are inexpensive
10. Questions to think about
1. How to detect and indicate RS422 signals
2. How to detect and indicate RS232 signals
3. Design a 4-bit 8-word display board
1) Power supply: DC12
2) Interface: RS232
3) 4-bit 3" 8-word (connected together)
4) Brightness detection
5) Secondary dimming
4. Design a 33-bit 1" 8-word display board
1) Power supply: DC5V
2) Interface: RS232
3) 3 rows of 11-bit 8-word, divided into 4, 3, 4 groups, with intervals between rows
4) Minimum system of single-chip microcomputer
5) Decoding logic
6) Display driver and driver device
5. Design an interface board for PCL725 and MOXA C168P
1) Power supply: DC5V
2) Interface: PCL725/MOXA 8 RS232
1. PCL725, upright DB37, hole
2. MOXA C168P, DB62 bend
3) Switch output signal conditioning: 6 solid-state relays and 8 relays, can be controlled and driven by any signal, interface: solid-state relay 5.08 vertical, relay 3.81 vertical
4) Switch input conditioning: dry contact closure is optional 1 or 0, interface: 3.81 vertical
5) RS232 conditioning:
1. LED indication
2. The first 4 channels are full RS232 signals, and the last 4 channels only need TX, RX, and 0
3. No need for photoelectric isolation
4. Interface form: DB9 (pin) upright
Part 2: Software knowledge
I. Assembly language
II. C51
This part can be learned from N development boards available on the market. As for the first part, someone needs to guide you.
Why should we master this knowledge?
In fact, electronic engineers put a bunch of devices together, inject ideas (programs), and complete the original
The higher the skill required, the more complex the function,
The lower the cost and the greater the demand for the corresponding things in the market, the more successful it is. This is the essence of electronic engineers.
The difference between the cost and the product sold is what the company is pursuing.
To find such applications in the market; for electronic engineers, it is to follow the requirements or applications proposed by the boss
Certain design principles (lowest cost, highest reliability, smallest circuit board, most powerful function, etc.) are implemented in the shortest possible time.
The shortest time is directly related to the proficiency, work efficiency and working time of the electronic engineer.
That's the value of an electronics engineer.
Abstracting electronic products into a hardware model consists of the following components:
1) Input
2) Processing core
3) Output
The input possibilities are basically:
1) Keyboard
2) Serial interface (RS232/485/can bus/Ethernet/USB)
3) Switching quantity (TTL, current loop, dry contact)
4) Analog quantity (4~20ma, 0~10ma, 0~5V (balanced and unbalanced signal))
The output basically consists of:
1) Serial interface (RS232/485/can bus/Ethernet/USB)
2) Switching quantity (TTL, current loop, dry contact, power drive)
3) Analog quantity (4~20ma, 0~10ma, 0~5V (balanced and unbalanced signal))
4) LED display: light-emitting tube, eight-character
5) LCD display
6) Buzzer
The main processing cores are:
1) 8-bit MCU, mainly 51 series
2) 32-bit ARM MCU, mainly atmel and Samsung series
The 51 series of single-chip microcomputers can only be used for some simple applications. To put it bluntly, this chip is only used for single
If you do too much, it is better to use arm to do it; you can also add an operating system on arm, and the program can
Reliable and easy to write.
Samsung's ARM has been popular recently. It is cheap and has Ethernet and USB interfaces. Zhou Ligong's development system
It is also cheap. As a product for learning ARM, it should be the best; as an industrial-grade control, is it suitable?
The company uses the atmel ARM91 series to develop an outdoor
The product was used outdoors in Beijing without any ventilation or heating measures from May last year to now.
It is running well and there is already a successful application case.
But for beginners, they should start with 51. On the one hand, 51 is still an entry-level chip.
If you have a good hand, you can go through the above concepts; many special microcontrollers are also based on the 51 core.
On this basis, some I/O, A/D and D/A are added; it also lays the foundation for learning higher-level microcontrollers and ARM in the future.
Besides, which boss would put ARM-level development in the hands of a novice who has not even learned 51?
It is not necessary to do complex parallel expansion on 51, such as expanding I/O ports and A/D, D/A, etc.
You can directly buy a microcontroller with A/D and D/A; or directly use ARM, which has many I/O ports.
Use I2C interface chips to expand I/O ports and A/D, D/A, and SPI interface to expand LED display, for example:
MAX7219 and other chips.
Some older books on the market contain some examples of parallel expansion, such as: RAM, EPROM, A/D,
D/A, etc., I don't think it's necessary to read them anymore, just know that they existed in history;
This knowledge is an element that all products have, so you need to learn it and then apply it in a specific way.
Let me tell you a little story: a savage exposing himself.
Once upon a time, there was a farmer who rested in the sun after working in winter. It was so comfortable.
He thought, I should present such a comfortable enjoyment to the king so that he can also enjoy it.
So he excitedly went to the palace and presented his valuable experience to the king.
I am now like this farmer, sharing my valuable experience with you. I hope you can give me more valuable suggestions.
; You can hit me with a brick, or scold me, it doesn’t matter, haha, whatever.
Lesson 1: 51 MCU Minimum System
In fact, the core peripheral circuit of the 51 single-chip microcomputer is very simple, a single-chip microcomputer + a watchdog + a crystal oscillator
+2 magnetic sheet capacitors;
1. MCU: Atmel's 89C51 series, Winbond's 78E52 series, and Philips' series are all inferior.
Not much; now there are some ISPs (online downloads), which makes it easier to use;
2. Watchdog: There are many types. I often use max691/ca1161 and DS1832. It depends on personal habits.
Chip operating voltage, packaging, etc. Max series and DS series, as well as IMP company, there are many types, generally only need
It only needs to have the most basic functions. I used max691 before, but max691 is more expensive because it has a power supply.
The battery switching function was added, and later new circuit boards were all designed using CA1161.
In circuit design a long time ago, some people may still use it now, using a resistor and a capacitor to achieve the same
However, such a reset circuit is unreliable. Why is it unreliable? You can find it on the Internet.
More importantly, the 51 series of single-chip microcomputers are more susceptible to interference;
Having a watchdog circuit is not enough. When the program runs away, it cannot come back and will die.
The usual practice is to buy a dedicated watchdog circuit to complete the functions of the reset circuit and the watchdog circuit.
The information of these chips is easy to find on the Internet, usually using Baidu search; see the PDF
If you see the words, click to download; it is also best to use FlashGet to download;
These materials are usually in PDF format, so a PDF reader is also required.
Baidu website: http://www.baidu.com
Skycn download URL: http://www.skycn.com/soft/879.html
PDF reader download website: http://www.chinapdf.com/download.htm
In fact, with Baidu and other search engines, it is very convenient to download the information of these chips, which is more convenient than CD-ROM.
No need to look for it everywhere.
The anti-interference ability of single-chip microcomputers is different. If your product is working in an environment with relatively large interference
You can try different brands of single-chip microcomputers. I used to work in an optoelectronics institute, doing the control of YAG laser therapy machines.
When the pulse laser power is discharged, the energy is very large.
After taking measures such as photoelectric isolation, it still didn't work; later, we chose Intel's 8031 and it worked.
He said: At that time, Philips' microcontroller had the worst anti-interference performance, which might be because Philips was mainly used in civilian applications.
I don't know what's going on now, if anyone knows please tell me.
The input and output lines of the microcontroller are the most likely to introduce interference; in the case of severe interference, all
Some lines are optically isolated.
3. Crystal oscillator: 11.0592M is generally used because it can accurately obtain 9600 baud rate and 19200 baud rate;
You can use 36.864M, which is 20 times the frequency of 1.8432M. I have seen it used on other people's circuit boards, but I don't have it either.
These two crystals are easy to buy and the price is the same as the 12M one. The book says that the 12M crystal can also be obtained.
The baud rate is 9600, but when it is actually used, it will make mistakes every once in a while, as if the error is accumulated.
Same, quite strange.
Even if your microcontroller system does not use the RS232 interface, you can also make an RS232 for testing or pre-
There is no harm in waiting, unless your microcontroller system does not have enough ports.
4. Magnetic sheet capacitor: 22pf~30pf. You can find out in some books what crystal frequency corresponds to what magnetic capacity.
However, I just use them casually. Anyway, there is no problem under 11.0592M.
When you reach a higher frequency, it is best to look for information.
See the following circuit diagram:
If your MCU system does not work, check the following steps:
1. Check the reset output of the watchdog. If possible, add an LED to the board and pull it down so it looks better.
Convenient; if the watchdog reset signal is present, go down;
2. Check the MCU to see if there is any problem with the pins; generally, the programmer can write the program, which means the MCU is
Good; it is best to have a verified microcontroller on hand with a simple program inside, such as
A square wave with a duty cycle of 1 second is output on each port line, etc., which can be measured using a multimeter.
One more sentence: When designing a product, you should pay attention to the key areas: power supply, serial port, watchdog output and input, I/O
Different colors of LED indicators can be added to the ports to facilitate debugging; for large-volume products, some LEDs can be removed.
On one hand, it reduces costs, and on the other hand, it keeps the process confidential;
3. Check the magnetic chip capacitors again. Some ceramic chip capacitors are of poor quality, so just replace them. By the way, it is best to replace the device.
Use solder desoldering tape to absorb the tin in the pad, and then pull out the device, so as not to damage the vias in the pad;
When soldering the new ceramic capacitor, use a multimeter to measure it to make sure it is good before soldering;
4. Finally, you have no choice but to replace the crystal oscillator; remember to buy a good crystal oscillator, some brands are of better quality.
5. When testing according to the above steps, remove the irrelevant peripheral chips; because some of them are peripheral devices
The fault caused the microcontroller minimum system to not work.
Lesson 2 Basic chips and discrete devices
2.1 Brief description
2.2 74 series
2.3 CD4000 series
2.4 Optocoupler and phototube
2.5 Transistor
2.6 Capacitor and resistor
2.7 Solid-state relay
2.8 Relay
2.9 Transformer and three-terminal regulator
2.10 Switching power supply chip
2.11 Packaging knowledge, chip batch number, etc.
2.12 Connectors
2.13 Knowledge of device selection
Lesson 3 Digital input and output
Lesson 4 Communication interface of single-chip microcomputer
Lesson 5 Hardware concept of single-chip microcomputer system design
Lesson 6 Framework of single-chip microcomputer program (assembly version)
Lesson 7 Analog input and output
...
Please give more valuable suggestions.
Guaranteed practicality. If there are some routines in the program, they have been tested and can be used; in fact
This is part of the program of some of my early products; sorry, it's all compiled.
I only have more time to write on weekends, and I can guarantee one lesson a week; I try to be ahead of schedule, but it depends on
It depends on whether I am busy at work.
There are some reference books on the market. I went to Beijing Zhongfa Market this morning and I remember the following reference books.
Better:
1. Zhou Hangci: "Microcontroller Programming"
2. Xu Hanfang: "MCS-51 Microcontroller Structure and Design"
3. He Limin: "......"
These are basically enough; many of the others are translations of materials; if you are not good at English, you can take a look;
If you are good at English, you don't need to do this. You can save money on electricity and buy development systems, programmers, development boards, etc. What do you need?
Just download the PDF file.
If you want to be an electronic engineer, you need broadband. It is definitely worth installing a monthly adsl or long and wide bandwidth at home.
In fact, everything is available on the Internet. It is a network database. Make good use of it.
The Internet has its own golden house and its own beautiful woman...
Lesson 2 Basic Chips and Discrete Devices
2.1 Brief Introduction
It is necessary to introduce the following series of chips and discrete devices.
In addition to the microcontroller as the core of the controller, as a product, it is composed of many things; therefore, when talking about the system
Before we start building a new system, let's first take care of all these little bits and pieces. Just like a house, it has various components.
The following things are like bricks and tiles, and they are indispensable.
2.2 74 series chips
Download addresses for 74 series chips:
http://www.dainau.com/TTLDATASHEET.htm
http://www.100y.com.tw/asp/class36_40.htm
http://www.mcu51.com/download/digitpdf/74xx/default.htm
The 74 series chips are an old family, and most of them are no longer used. However, in fact,
In the previous system, some chips can still be seen, and some chips are still used in the system, such as:
1. 7404 – 6 inverting gates
Download address:
http://www.hqew.com/document/detail.asp?pdid=125533
Invert the input TTL logic, such as: 0->1, 1->0
2. 7407 – 6 open collector gates
Download address:
http://www.hqew.com/document/detail.asp?pdid=125518
Since the collector open gate can be connected to a high voltage, up to DC30V, and the maximum current is 39mA, I usually
It is used to drive high current loads such as 8-digit digital tubes and relays; the internal structure of the open circuit gate is a Darlington tube, and the input
The logic output is positive;
a similar chip is 7406, which is just an inverting open-circuit gate.
3. 74LS573 and 74LS373 – 8 Data Latch
74LS373 download address:
http://www.hqew.com/document/detail.asp?pdid=129171
74LS573 download address:
http://www.yddz.net/yddzsourse/pdf/74hc573.pdf
Introduce several concepts:
1. Truth table
See page 2 of the PDF for 74LS373:
Dn LE OE On
H H L H L
H L L
X L L Qo
X X H Z
This is the truth table, which shows the output of this chip under certain inputs and other conditions.
Each chip's datasheet has a truth table.
Boolean logic is relatively simple, so I won't go into details here.
2. High impedance state
That is, the output is neither high level nor low level, but high impedance state; in this state, you can
Multiple chips are connected in parallel for output; however, only one of these chips can be in a non-high impedance state, otherwise the chip
The chip is burned;
the concept of high impedance state can also be used in RS232 and RS422 communications.
3. Data latch
When the input data disappears, the data still remains at the output of the chip;
this concept is often used in parallel data expansion.
4. Data Buffering
Enhanced drive capability. 74LS244/74LS245/74LS373/74LS573 all have data buffering capabilities.
OE: output_enable, output enable;
LE: latch_enable, data latch enable, latch means latch;
Dn: nth input data;
On: nth output data;
Let's look at this truth table again. The meaning is as follows:
Row 4: When OE = 1, the output is in high impedance regardless of Dn and LE;
Row 3: When OE = 0 and LE = 0, the output remains unchanged;
Row 2 and Row 1: When OE = 0 and LE = 1, the output data is equal to the input data;
Combined with the waveform diagram below, this is how it is done in actual application:
a. OE = 0;
b. First output the data from the microcontroller's port line to Dn;
c. Then change LE from 0->1->0
d. At this time, the data you need to output is locked in On, and the input data will not affect the output even if it changes.
In fact, the microcontroller is now busy doing other things, such as serial communication, scanning the keyboard...
The resources of the microcontroller are limited.
When the microcontroller expands parallel data in RAM mode, using the instruction movx @dptr, A, this
These timings are implemented by the microcontroller.
There are also parameters that require time in the table below, you don't need to worry about them, because these parameters are in the order of tens of ns.
In addition, for the MCU under 12M, each instruction cycle is at least 1us, which can be fully realized;
If you implement this logic yourself, similar instructions are as follows:
mov P0,A ; output data to parallel data port
clr LE
setb LE
clr LE ; the above three instructions complete the change of LE waveform from 0->1->0
74LS573 is logically identical to 74LS373, except that the pin definitions are different.
Each is on one side, making it easy to route the PCB; so everyone likes to use this chip.
4. 74LS244 – Data Buffer
Download address:
http://www.mcu51.com/download/digitpdf/74xx/74F244.pdf
The data output capability is relatively strong, and the output current can reach more than 40mA;
4 buffers are divided into 2 groups, with high-impedance control ports
5. 74LS245 – Bus Buffer
http://www.mcu51.com/download/digitpdf/74xx/74F245.pdf
Bidirectional data interface, usually seen on ISA boards;
in early 51 systems, this chip was often seen in order to expand RAM, eprom, A/D, D/A, I/O, etc.
;
In order to enhance the driving ability, sometimes to isolate the input and output, mainly for the convenience of wiring, such as 74LS573
Like this, the input and output are on one side, this piece is often used
6. 74LS138 – Three to Eight Decoder
http://www.mcu51.com/download/digitpdf/74xx/74F138.pdf
In the early expansion of the 51 system, this chip was often used as an address selector.
Another similar chip is the 74LS154, which is a 4-16 decoder, but is even rarer now.
If you are interested, you can study the relevant chapters in He Limin's classic book.
It is enough to know that there is such a chip.
2.3 CD4000 Series
The CD4000 series chips have some electrical characteristics that are different from the 74 series, such as:
1) a wide voltage range, which should be able to work in the range of 3V to 15V, high input impedance, and poor driving ability.
1) The functions of the two devices are basically the same;
2) When inputting, 0 is below 1/2 of the working voltage, and 1 is above 1/2 of the working voltage;
3) When outputting, 1=working voltage; 0=0V
4) The driving capability is very poor, and it can only carry 1 TTL load at most when designed;
5) If a pull-up resistor is added, it must be at least 100K resistor;
6) The only thing that can be used now is the counter. The counter of CD4060 can count to 14 levels of binary serial/
The frequency divider of this 74 series cannot reach such a high level;
Download address:
http://www.100y.com.tw/asp/class36_40.htm
http://www.100y.com.tw/pdf_file/CD4060.PDF
2.4 ULN2003/ULN2008
Its internal structure is also Darlington, a chip specially designed to drive relays.
The output of ULN2003 allows 200mA of current to pass through the IC, and the saturation voltage drop is
VCE is about 1V, and the withstand voltage BVCEO is about 36V. The external load of the user output port can be estimated based on the above parameters.
. It adopts open collector output and has large output current, so it can directly drive relays or solid state relays (SSR)
And other external control devices, can also directly drive low-voltage bulbs.
This chip is often seen in industrial control boards.
There is an identical model: MC1413, but it seems that this model is rarely seen now, but the pins are similar.
2003 fully compatible.
ULN2003 can drive 7 relays; ULN2008 drives 8 relays.
ULN2003 download address:
http://www.hqew.com/document/detail.asp?pdid=148212
ULN2008 download address:
Not found. Strange.
2.5 Optocoupler
What is the use of optocouplers? Optocouplers are used to isolate input and output, mainly to isolate input signals.
In various applications, there are often some long-distance switch signals that need to be transmitted to the controller. If these signals are directly
When these signals are connected to the I/O of the microcontroller, there are the following problems:
1) The signal does not match. The input signal may be an AC signal, a high voltage signal, a button or other dry contact signal.
2) Long connection lines are prone to interference, lightning strikes, induced electricity, etc., and are unreliable without isolation.
Therefore, an optocoupler is needed for isolation and access to the microcontroller system.
Common optocouplers include:
1) TLP521-1/ TLP521-2/ TLP521-4, which are 1 optocoupler, 2 optocouplers and 4 optocouplers respectively, from HP
And ***'s Toshiba Corporation produced.
Download address:
http://www.100y.com.tw/pdf_file/TLP521-1-2,4.PDF
The working current of the light-emitting tube should be 10mA, with a high conversion rate;
when working at 5V, the pull-up resistor should be no less than 5K, generally 10K; if it is too small, it is easy to damage the optocoupler;
2) 4N25/4N35, manufactured by Motorola
Download address:
http://www.100y.com.tw/pdf_file/4N25-8,35-7,H11A1-5.PDFIsolation
voltage up to 5000V;
3) 6N136, manufactured by HP
Download address:
http://www.100y.com.tw/pdf_file/6N135-6.PDF
To open 6N136, a relatively large current is required, about 15~20mA, in order to achieve high-speed data transmission.
If the speed requirement is not high
, TLP521-1 can also be used, and the actual transmission speed can reach 19200 baud rate
.
The choice of optocoupler depends on the application scenario. TLP521-1 is the most commonly used and cheap, about 0.7 to 1 yuan.
If a high isolation voltage is required, choose 4N25/4N35, which is about 3 yuan.
If high-speed data transmission is required in communication, choose 6N136, which is about 4 yuan.
The principle block diagram of the optocoupler application is as follows:
1. Input dry contact isolation
2. Input TTL level isolation
3. Input AC signal isolation
4. Output RS232 signal isolation
5. Output RS422 signal isolation
In addition to isolating digital quantities, optocouplers can also be used to isolate analog quantities, which will be described in later chapters.
2.6 Transistor
2.7 Photoelectric tube
2.8 Capacitor
2.9 Resistor
2.10 Solid-state relay
2.11 Relay
2.12 Transformer and rectifier bridge
2.13 Three-terminal regulator
2.14 Switching power supply chip
2.15 Packaging knowledge, chip batch number, etc.
2.16 Connector
2.17 Knowledge of device selection
2.6 Transistor
2.6.1 Four working states of transistors
1) Saturated conduction state
Saturation conduction = 0
2) Cut-off status
Saturation conduction = 1
3) Linear amplification state
When used as a low-frequency amplifier, please refer to books on electronic circuits for details;
4) Non-linear working state
In radio communication systems, it is used as a mixer, etc. For details, please refer to books on electronic circuits;
I remember that Nanjing Institute of Technology, now Southeast University, had a set of 5 books on "Electronic Circuits" in the early 1980s.
It is a book for electronics majors, which is difficult to understand. Now, even among students majoring in electronics, the difficulty should be reduced.
What are the complex parameters of the transistor? In actual use, even analog circuits and nonlinear
Circuits are all integrated circuits, so who would still use transistors to make them themselves? If you need it, you can learn it now.
And. This set of books is very strong. The authors must have been great people in that era.
Learning the parameters of triodes is very complicated. If current non-electronics college students or junior college students still learn these
I can only say that the school is misleading its students.
Many schools are expanding enrollment. Many students have studied for four years and learned a lot of outdated theories that are not relevant to practical things.
There is no connection at all. I don't know what 7407 is used for, and I don't know the states of the transistor. I can only be speechless.
It can be said.
Therefore, after studying for 4 years, there is still a gap between what companies need and what they need to do. Smart students need to start all over again.
Seize the opportunity to study and do an internship, so that you can quickly make up for this lesson in practical application.
Let’s get back to the topic.
See the figure below:
When the microcontroller's port line output level is 1, the be junction of the transistor is turned on, the ce junction is turned on, and the output voltage value is
0V;
when the output level of the microcontroller port line is 0, the be junction of the transistor is not conducting, the ce junction is cut off, and the output voltage value is
5V;
In the application of this digital circuit, the transistor is equivalent to an inverting open gate.
To calculate whether it is conductive, the formula is as follows:
I = B (magnification, the Greek letter beta) × Ibe
When Ice<I, it is saturated conduction;
The greater the phase difference, the deeper the saturation, the smaller the Vce, and the smaller the output internal resistance of the transistor;
This concept is used in photoelectric tubes.
When designing, do some calculations and have an idea in mind; try it on a circuit board, and if it works, then that's it.
Measure the Vce value, it should be at least less than 0.1V.
The commonly used PNP transistor is 2N5551, which has no problem driving 40mA LED (voltage at 24V), buzzer, etc.
.
2.6.2 Specific Applications of Transistors
In fact, there are already products like 7407 and ULN2003 that can replace the role of triodes in digital circuits; however,
Sometimes it is limited by the PCB area, sometimes it is to reduce costs, and sometimes it is for layout convenience.
When outputting, you can still use transistors for driving.
For example: driving a buzzer; often the buzzer in the system is far away from other driving devices, relays, etc.
Far; at this time, there is no need to use a 7407 or ULN2003 to drive; the driver interface is as follows:
Re: From 51 Beginner to Electronic Engineer (Repost)
2.7 Photocell
There are two types of phototubes:
1) Reflective photocell
2) Through-beam photocell
These two products can be divided into conditioned and unconditioned products on the market;
These two types of phototubes are heavily advertised in Electronics World and Electronic Technology Applications magazines.
Both.
What I mean by well-conditioned is that the internal current limiting resistor and output amplifier drive circuit have been added.
The point is that there are only 3 wires, 2 for power supply and 1 for output signal, TTL level; however, sometimes there are some restrictions
, what should I do if I need to use something that has not been conditioned?
See the figure below: Photoelectric tube principle block diagram
When using this unconditioned photoelectric tube, you need to make a small circuit board and add a current limiting resistor to the light-emitting tube.
, add a pull-up resistor to the collector of the phototransistor to 5V, as shown in the figure below: Phototransistor working block diagram 1.
However, I found that the output signal was unstable, especially when using a relatively long cable to transmit to a single
The reason, I think, is that the reflected or incident infrared light falls on the target of the phototransistor.
On the surface, the light intensity fails to cause the phototransistor to be deeply saturated, making the output internal resistance too large, and the environmental noise and electrical
The interference signal of the cable is easily superimposed on the line;
In order to work reliably, a current limiting resistor is added to the output end of the phototransistor, following the structure of the Darlington tube.
When there is no light, the B junction of NPN is saturated and turned on, and the output voltage is 0V; the actual measurement is less than 0.1V;
When there is light, even weak light, the 2N5551 is turned off and the output voltage is 5V. Replace the 3K resistor with a larger or smaller
The resistor can adjust the sensitivity of the phototransistor output.
You can analyze the specific working process yourself and do an experiment.
2.8 Capacitors
2.8.1 Main types of capacitors
There are several major categories of capacitors:
1) Electrolytic capacitor
2) Monolithic capacitor
3) Magnetic sheet capacitor
4) Gallbladder (gold on the left and dart on the right) electrolytic capacitor
5) Polyester capacitor, etc.
The indicators of capacitors are: withstand voltage and capacitance. For example: 220u/50V, that is, the withstand voltage of this electrolytic capacitor is
The value is 50V and the capacity is 220u.
The capacity of a capacitor is related to the dielectric of the capacitor.
As the name implies:
Electrolytic capacitors use electrolyte as the medium and aluminum as the electrode;
Monolithic capacitors use stone as a dielectric;
Magnetic sheet capacitors use magnetic sheets as the medium;
The electrolytic capacitor uses electrolyte as the medium, but the electrodes are made of gold.
Polyester
capacitors use polyester as the dielectric.
Interested netizens can take apart a capacitor and take a look.
2.8.2 Application scenarios of capacitors
1. Power supply stabilization and filtering
Electrolytic capacitors are mainly used for voltage stabilization and low-frequency AC filtering; high-frequency filtering uses magnetic sheet capacitors and monolithic capacitors.
When the electrolytic capacitor is used as a voltage stabilizer, it is connected to the output end of the rectifier bridge and the three-terminal voltage stabilizer to stabilize the voltage .
Its working mechanism is equivalent to a reservoir. When the wavy water from upstream reaches the reservoir, it becomes smooth.
.
However, the electrolyte of aluminum electrolytic capacitors will dry up over time, so a margin needs to be left when designing.
Ensure the system works properly throughout its lifespan.
When some remotely powered DC power supplies are connected to the input terminal of a circuit board, it is necessary to add a
A large electrolytic capacitor, usually 220u/25V, so that when the circuit board needs power, it is not directly
Instead of taking power from the power supply, it takes power from the capacitor, which can provide a stable current supply;
However, electrolytic capacitors can only filter out low-frequency fluctuations; for high-frequency fluctuations in the DC power supply, you can add a
0.1u or 0.01u monolithic capacitor or magnetic chip capacitor.
Many textbooks point out that a 0.1u or 0.01u monolithic capacitor should be connected to the power supply and ground of each chip.
Or ceramic capacitors to solve the power switching noise caused by the wiring inductance of the circuit board during the power supply process of the chip.
Acoustic spikes. The capacitor under this effect is called a decoupling capacitor. This is the conventional design of the circuit board;
2. Timing parameters
For devices like 555 that require external capacitors to generate stable pulses, polyester capacitors are the first choice.
, the polyester is wound layer by layer, and the relative value of the change in the area of the polyester caused by temperature change is much smaller
The change value of the dielectric stone of the monolithic capacitor caused by temperature change.
3. Generate other voltages
Some chips that need to generate other voltages from a single voltage, such as max232, require external capacitors to achieve this.
.
Refer to the max232 technical data.
External 01.u tube capacitor.
2.8.3 Capacitor Packaging
Capacitors come in different packages: through-hole and surface mount.
The normal withstand voltage of electrolytic capacitors in surface mount packaging does not exceed 25V, and the capacitance does not exceed 100u.
The other capacitors, magnetic discs and monolithic components are all in surface mount packaging.
2.9 Resistors and Potentiometers
2.9.1 Types of resistors
2.9.1.1 Ordinary resistor
Resistors can be divided into carbon film resistors and metal film resistors according to the process;
According to the power, it can be divided into low-power resistors and high-power resistors. High-power resistors are usually metal resistors.
A metal (aluminum) heat sink should be added outside the metal, so that the power can be more than 10W;
It can be easily seen in the electronic accessories market that specializes in selling resistors.
Metal resistors are usually used as loads or as outdoor heaters for small devices, such as some decoding devices in CCTV.
It can be seen in the instrument box and all-weather protection cover.
Resistors play the role of current limiting and voltage dividing in circuits. Usually 1/8W resistors are sufficient.
In the 7-segment LED, the difference between the voltage drop of the LED and the supply voltage must be considered, and then the maximum current of the LED must be considered.
Usually it is 20mA (ultra-bright LEDs), and if it is 2×6 (2 rows of 6 in series), the current is 40mA.
Different manufacturers use different materials, and the voltage drop is different. Therefore, it is necessary to add an electrical test, but don't
If the LED current exceeds 20mA (single LED), increasing the current will not increase the brightness, but the LED life will be shortened.
The life will drop, and the size of the current limiting resistor is the voltage drop divided by the current. The power of the resistor can then be calculated.
This uses junior high school knowledge is enough.
2.9.1.2 Potentiometer
A potentiometer is an adjustable resistor. When I was studying physics in junior high school, the teacher took a large cylindrical object and
There is a slider on the side, which is very similar to this thing.
Its resistance value varies between 1 and n.
N=102, 502, 103...
102=10*10 to the power of 2, which is 1000 ohms
. The same goes for 1K, 502=5K.
This method of expression is the same as that of capacitance.
Capacitance 104 = 10*10 to the fourth power pf. The basic unit of capacitance is pf. 1u = 1000000pf. Therefore,
104=100000pf=0.1u;
Potentiometers are divided into single-turn and multi-turn potentiometers.
Single-turn potentiometers are usually grayish white, with a cross-shaped adjustable knob on the surface. They are placed in a fixed position before leaving the factory.
In terms of position, it is not at the 2nd end;
Multi-turn potentiometers are usually blue, and the adjustment knob is a flat-blade, which can be adjusted with a small flat-blade screwdriver;
Multi-turn potentiometers are divided into two types: top adjustment and side adjustment. They are mainly convenient for circuit board debugging.
Some are instrumentation equipment, usually analog circuits, with some uncertain factors that need to be adjusted to achieve
The most ideal effect; some devices themselves need to output a variable thing, such as voltage and current,
Need a potentiometer.
2.9.1.3 Resistor array
It is a SIP n package. The most commonly used ones are 9-pin resistors with resistance values of 502 and 103; SIP9 is an 8-pin resistor.
The resistors are packaged together, and one end of the 8 resistors is connected together, which is the common end. A small white dot is used on the resistor array.
The resistor is usually black, but also yellow; P0 of the 51 system needs a resistor to pull it up, otherwise,
When used as input, data cannot be read normally; when used as output, it is OK to connect to 7407, and no need to connect to
Pull resistor; however, it still doesn't work when connected to other chips. If you are interested, you can look at the structure of P0 of 51; if you are not interested,
Fun, just follow the example and do as you are told.
2.9.1.4 Photoresistor
When the light intensity shining on the photoresistor changes, the resistance value also changes. Obviously, this is the characteristic of semiconductor materials.
Using a photoresistor can detect changes in light intensity.
Question 1:
There is an LED display device that requires that when the light intensity changes, the brightness of the LED changes with the light intensity;
The stronger the voltage, the brighter the LED; vice versa. How to use a microcontroller to achieve this function? It can be multi-level dimming, such as 8 levels
Dimming; it can also be made into stepless dimming.
2.9.2 Resistor Packaging
The resistor packaging includes surface mount and axial packaging.
Axial packages include: axial0.4, axial0.6, axial0.8, etc.; axial means axis in English.
The most commonly used package for surface mount resistors is 0805 ;
of course there are larger ones; but I don't think larger resistors
It is very commonly used.
The package of the potentiometer can be easily found in the Protel book. However, if it is used directly, there may be a
Lao Shu made this mistake in the early days, which made it difficult to install the components next to the potentiometer.
There is a difference between working on hardware and software. People who work on hardware must be precise.
A small mistake in the hardware will cause the board to be rebuilt; because the product cannot have flying wires.
This small error is equivalent to a statement in the software, which can be quietly changed during the software debugging stage.
Unnoticed; on the PCB, especially disgusting. And everyone knows it - the boss knows best.
What is precision?
1. Have an accurate understanding of the goals of the work you want to achieve;
2. Be clear about the role of each component in your circuit diagram; if you don’t understand, you can find a
Ask an expert and get confirmation; if you are not sure, you can try it first;
3. The packaging of each device must be strictly controlled, and the shape and appearance must be completely consistent; and
Consider whether the space has an impact on other board components; the space between the edge connector and the edge of the circuit board.
The distance between the ISA and PCI edge connectors and the baffle must be fully understood before making the circuit board;
It's just a waste of money and time;
If you are not sure about the distance between the edge device and the edge, you can find 3 people, each of whom calculates
Do it once and take an average value, and that's basically it.
4. You must be sure whether the resources of the microcontroller can accomplish this task, such as the CPU speed, word length, and internal memory.
Whether the memory is large enough and whether the program memory is large enough requires careful planning;
5. After the schematic diagram is approved by the experts, the drawn PCB needs to be checked for network to ensure that it is consistent with the schematic diagram.
All consistent;
2.10 Relays, solid-state relays
2.10.1 Relay
A relay uses the magnetic force generated by the relay coil after power is applied to attract two electrodes together.
The physics in middle school or high school has its principles. If you are interested, you can open one and take a look. It is very interesting.
Relays have:
1) Common terminal: COM
2) Normal open: normal open, NO
3) Normal close: normal close, NC
Main indicators of relay:
Operating Voltage:
There are 2 types of working voltage: DC and AC;
On the PCB, it is usually DC; AC relays are usually AC24V, of course, there are also AC220V
. Domestic AC relays are much cheaper than imported ones, such as idec, OMRON, and fujitsu. Of course,
The quality is also worse.
You can search for relays specifically on Baidu, which will provide introductions to some manufacturers' products.
The commonly used low-power relays are mostly national, OMRON also has them, which are cheaper and come in a box of 50.
Commonly used voltages are:
DC5V/DC9V/DC12V/DC24V, etc.;
According to the number of contacts, it can be divided into:
Single Pole Single Throw/SPST
Single Pole Double Throw/SPDT
Double Pole Double Throw/DPDT
Quad-pole double-throw, etc./?
It is also divided according to the contact capacity.
Generally, the voltage is DC30V/1A or DC30V/2A, AC110V/0.2A. If the voltage is larger than that, the relay cannot be used.
Because when the contacts switch and the current passes through, an arc will be generated, burning the contacts and making the switching unreliable;
Yes, solid state relays can be used.
In fact, the task of the relay on the PCB is to give a dry contact signal, which is used as a control signal.
What is transmitted is a signal, not energy. Or control a high-power switch, etc.
To control the transfer of power; however, the latter is not as convenient as a solid-state relay.
Relays are usually packaged in DIP16 or larger. There are also smaller relays, but the price is much lower than that of DIP16.
not much.
Note: DIP16 relays only have 8 pins; so when designing the package, do not use DIP16 directly for the sake of convenience.
, which makes it easy to solder the wrong part when soldering, resulting in errors. To design a special package for a relay, there should be several
Just use a few feet.
2.10.2 Solid State Relay
To put it simply, a solid-state relay is a zero-crossing triggered thyristor that is triggered by a light-emitting diode.
It can be said that it is very similar to an optocoupler, and also has 4 pins, but the difference is:
4) Directly use DC voltage control; it can be considered that there is already a current limiting resistor inside;
5) The end that receives the optical signal is a zero-crossing triggered thyristor;
It can be said to be an electronic switch, a contactless relay.
Because there are no contacts, large currents can pass without arcing, and the service life has nothing to do with the number of switches.
The working life of the relay whose contacts are used as signals is 1 million to 3 million times. You can check the technical
manual;
Solid-state relays can be considered to have unlimited times, so solid-state relays are used in situations with high current and frequent switching.
device.
The signal passing through the solid-state relay contacts is usually an AC voltage, but there is also a DC voltage.
Solid-state relays can pass AC220V or AC380V or below; its two indicators are:
1) Working voltage, usually DC5V and DC12V, there are also DC24V;
2) Working current: AC220V/1A/2A/4A.
The quality of domestic solid-state relays is good, no different from imported ones, but the quality of the packaging is too poor.
They are all different, and the soldering on the circuit board is crooked and unsightly; as for the low-power domestic relays
It is relatively rare on the market and people don’t dare to use it even if they have it.
Imported solid-state relays are from the United States and Japan. Those above 4A are more expensive. The most expensive OMRON solid-state relays are
The 2A version is only 8 yuan, and it is estimated to be cheaper if you bargain. It is small in size, and the packaging is absolutely accurate, and it can be neatly
Arrange on the circuit board, not taking up space;
2.12 Linear Power Supply: Transformer, Rectifier Bridge and Three-Terminal Regulator
What is a linear power supply? Why is it called linear? Lao Shu searched the Internet for information, but there was no answer. He had to wait.
Gao Ming taught me.
If the PCB needs power, it needs a power supply. There are two types of power supplies. One is a linear power supply, such as 7805, which is a linear power supply.
source;
One is a switching power supply, which directly rectifies and filters AC220V into high voltage, driving the power tube to work above 100Khz
, and then rectified and filtered into low voltage.
The working principle of the switching power supply can be found on Baidu.
Linear power supply needs power frequency transformer to transform AC220V into low voltage, which is rectified by full bridge and filtered by large capacitor.
The wave becomes a pulsating DC, which then passes through a three-terminal regulator to output a DC voltage.
The output end also needs a large electrolytic capacitor for filtering. Note that you need to choose a capacitor with a large enough capacitance and a high withstand voltage.
If the withstand voltage is not high enough, you will hear a sound. If the capacitor capacity is not high enough, the rectifier output voltage and output
If the voltage difference is not enough, the output voltage will have ripples and the microcontroller system will not work properly.
Usually the circuit board needs DC5V. Generally speaking, a 7805 circuit board plus a heat sink can also
The greater the power, the larger the heat sink.
Transformers come in a variety of sizes:
1. The transformers wound with ordinary E-type silicon steel sheets are now produced in the largest quantities by Xiongying in Puning, Guangxi.
It has passed the Great Wall certification, the quality is good, the biggest advantage is that it is cheap and has a large stock; the usual specification is single 9V
, 12V, dual 9V, 12V, etc.; maybe this place produces silicon steel sheets and has such mineral deposits.
2. Toroidal transformer, like an ellipse;
3. Recently, there seems to be more and more round transformers. The latter two types of transformers should have small magnetic leakage, less heat, and high efficiency.
The rate is high and it is used for high-power rectification. Of course, the unit wattage is also expensive. According to 1 yuan/W, the budget should be about the same.
More.
Both types of transformers need to be customized, and various specifications can be customized.
4. The transformers soldered on the circuit board are more famous for the Bingzi brand.
There is one in Qinhuangdao, which seems to be called Yaohua.
How to calculate how much power the transformer needs?
First, calculate the power consumption. For example: Dc5V/0.25A, which is 1.25W of power consumption.
The efficiency of 7805 is 50%, and the efficiency of the transformer is 50%, which means that a 6W transformer is needed.
The input voltage difference of Dc5V/0.25A is about 3V, and the voltage rectified by the 6V transformer is about 6×1.4＝8.4V
, which is almost the same. All choose AC6V/6W transformer. Then find a similar transformer on the market.
Just go up.
Note: The greater the current, the greater the voltage difference; when the circuit is working, you can use an oscilloscope to see the waveform of the power supply.
Not stable.
The 78 series chips are made by National Semiconductor Corporation, which is the largest and best manufacturer of them.
)'s LM780X and Motorola's MC780X.
The 78 series is a high-voltage differential voltage regulator chip. Now there is a low-voltage differential voltage regulator chip. For its mechanism, please refer to Mr. Sha Zhanyou's
Books. There are 4 series: LM2930, LM2937, LM2940C, LM2990.
If you need a larger power supply, either use a switching power supply or buy a ready-made linear power supply, such as Liaoning
Chaoyang 4NIC power supply has good quality and good price.
Appendix: An article found on the Internet:
The difference between switching power supply and linear power supply
The adjustment tube of the linear power supply works in the amplification state, so it generates a lot of heat and has low efficiency (about 35%).
In addition to the bulky heat sink, a large power frequency transformer is also required.
The transformer will be larger when the voltage output is high. The adjustment tube of the switching power supply works in saturation and cut-off state, thus generating heat.
Small, high efficiency (over 75%) and saves the bulky transformer.
A larger ripple (50mV at 5V output typical) will be superimposed. Connecting a Zener diode in parallel at the output can
To improve, in addition, because the switch tube will produce a lot of spike pulse interference, it is also necessary to connect in series in the circuit
Relatively speaking, linear power supply does not have the above defects, and its ripple can be made very small (5mV
Below). For places with requirements on power efficiency and installation volume, switching power supply is preferred.
Where power purity is required (such as capacitor leakage detection), linear power supplies are often used.
When isolation is required, DC-DC is now mostly used to power the isolated part (DC-DC has a high working principle).
Also, the high-frequency transformer used in the switching power supply may be difficult to wind.
2.14 Switching Power Supply Chip
Compared with linear regulators, switching power supplies are used on computer motherboards, industrial computer motherboards and various circuits.
The board plays the role of voltage conversion. For example, it converts low voltage, such as batteries, into a stable 3.3V or 5V
, or convert high voltage into DC5V, DC3.3V, or convert DC5V into 3.3V and 1.8V, for example, ARM
The circuit board needs such a chip, 3.3V to power ARM, 1.8V to power the core of ARM.
Because of the switch circuit, the power chip has a high operating frequency, low heat and high efficiency.
Similarly, chip giants such as MAXIM, LINEAR and TI are the most outstanding in power conversion chips.
Yue, both in terms of product variety and quality are excellent;
Netizens who often read the world of electronic products and electronic technology applications must have a deep impression of maxim's power chips.
There are so many different power chips that you can't choose the one you need.
In the maxim product tree, power supplies are classified as follows:
Power Supplies and Battery Management
Switchmode DC-DC Power Supplies 408
Isolated Power Supplies 22
Low-Dropout Linear Regulators 75
White LED Drivers 13
Low-Side MOSFET Drivers 14
High-Side MOSFET Drivers 6
ORing MOSFET Controllers 2
Battery Chargers 36
Battery Protectors, Selectors and Monitors 17
Regulator + Reset Circuits 4
Current Sense Amplifiers 22
LCD/ECB/CCFL Display Bias Supply 87
ALSO SEE: Hot-Swap and Power Switching
ALSO SEE: Voltage References
We often use Switchmode DC-DC Power Supplies, which are divided into n types.
The more familiar one is the step-down power chip, which is the so-called chip that drops from high voltage to low voltage.
; From low to high, of course it is the step-up power chip.
Electric shavers like Philips must have a power management chip inside. When the battery voltage drops, the power
When the battery is full of power, it can output a constant voltage, squeeze out the last bit of power in the battery, and be able to comfortably
Use for a long period of time.
For example, your circuit board only has DC24V voltage, but you also need a DC5V/2A power supply.
It is obviously not appropriate to use a linear regulator. If a DC/DC module is used, the cost is too high and the volume is relatively large.
Therefore, a chip must be selected to complete this function.
According to the complex choices given by maxim, select a few more items according to your requirements, and maxim will give a list
, select the chip from the list that best suits your needs.
The chips that Laoshu used to complete this function are: MAX724, LT1076; these two chips require 1
50uH inductor can output DC5V power supply; however, this switching power supply chip has an advantage that the input only needs
When the voltage fluctuates within the allowable range or the load changes, the output DC5V power supply is very stable.
The power supply range is from DC10V to DC40V, and max724 can output 5A DC5V power supply.
Maxim724 download link:
http://www.hqew.com/document/detail.asp?pdid=153160
LT1076 download link:
http://www.hqew.com/document/detail.asp?pdid=157742
The power chip used on ARM is TPS767D318 from TI.
Download Link:
http://www.hqew.com/document/detail.asp?pdid=122122
In Mr. Sha’s book, several power conversion chips are also introduced for reference.
If it is generated as an isolated voltage, for example, 5V is converted into isolated 5V and used in optocoupler, communication and other circuits,
It is not cost-effective to make the isolation circuit by yourself. It is better to buy a ready-made DC/DC module.
The ones are pretty good, like the Dc12V/DC5V500mA module that Laoshu often uses, which costs about 30 yuan and has good quality.
2.15 Device selection, chip batch number, packaging knowledge, etc.
When buying chips in the market, be careful not to buy old chips or disassembled chips; some old chips or disassembled chips can be used.
Some simply don’t work; even if they can be used now, their lifespan is definitely limited;
Old is old, and it is definitely not hidden from those who are interested; mainly from the newness of the chip pins, the chip printing
Observe the quality carefully.
Old chips often have uneven pins, dark tin, and the packaging tubes are not new enough; and the surface of the chip is often
The surface is white because it has been polished, and then the manufacturer's name, batch number, etc. are re-screened;
Therefore, it is best to buy laser-marked devices. Laser-marked products must be new or unused.
; And when buying, you need to pay attention to the batch number of the device, preferably the one produced in the last year or the last few weeks.
In short, don't waste your money and affect the quality of the product.
The same product has different quality from different manufacturers. I prefer American TI, Motorola MC,
MAXIM and LINEAR products; there are few fake ones;
For example, the max7219 chip has the following logo:
MAXIM
MAX7219CNG
0323PY
MAXIM is the manufacturer of the chip;
MAX7219CNG is the manufacturer's model number. CNG is related to the packaging and the subtle differences in the 7219 series of products;
03 refers to the year 2003; 23 refers to the 23rd week of the year; there are 52 weeks in a year, so this number will not exceed 52;
Laser marking is to form a dark mark on the chip that has a clear contrast with the chip surface;
Daheng Company has a laser marking machine business, but it does not necessarily mark on chips;
Sometimes, laser marking will produce a dark yellow mark, which is related to the laser power and chip packaging material.
From Beginner to Electronic Engineer Lesson 3 How to become a qualified electronic engineer?
Sorry, I haven't finished the second lesson yet, so I'll start another one. Old Tree used to be a teacher, and he has a habit of destroying people.
I have thought about this problem for a long time and have basically figured it out.
Many beginners on the Internet are asking: How to become a qualified electronic engineer?
There are many answers to this question. Lao Shu shares his own views.
Step 1 Getting Started - 51 Core and Basic Circuits
There are 1 billion Chinese people. How many college students graduate every year? I don't know. But I saw a photo.
The job fair was bustling with people coming and going, which was very shocking. There was never a moment when I felt that the Chinese people
The human resources are so abundant. But what have the students who graduate from today's universities learned?
These are theories that are disconnected from reality. Are they useful? Somewhat useful. However, in business, what is needed is reality.
So many companies don't want college graduates.
, I don't have the hands-on ability, I don't know what resistors and capacitors look like, what can I do?
They have high expectations for wages. When they are able to do something, they just leave.
The industry now prefers to use children trained in colleges, technical secondary schools, or even vocational schools. At least these children know how to
You know, many of them are talented, and some of them are even
They can be said to be smart, but it is because many people come from poor families and have been poor children since childhood, and have no conditions to receive good education.
Good education. Once given an opportunity, they will cherish it.
Today's universities are misleading many students. There is nothing wrong with expanding enrollment, but have the laboratories and classrooms been expanded?
Has the faculty expanded? At least the labs have not expanded. A graduate student I know said that only at a certain stage
Many instructors treat students like slaves.
If you learn something, you are lucky; if you are unlucky, you will just be the cheap labor of the tutor and learn nothing.
Things, but I did a lot of work.
However, since students have to get diplomas and take exams, there is no other way. How can they save themselves?
If you want to be an outstanding electronic engineer, Lao Shu can talk about his own views.
It is generally acknowledged that to be an electronic engineer, one should start from 51. No need for Lao Shu to ramble.
First, buy a development board, the cheaper the better, on which you can practice Keil C. It is best to buy a replica
Of course, this is not cheap, but I think it can be done by like-minded brothers.
Anyway, there are 24 hours a day, and each person takes 8 hours in turn. After a few months, the C51 language will be almost mastered.
Secondly, read Lao Shu's article to see what basic things you need to learn.
Go to Zhongfa to check out what resistors, capacitors, transistors, chips, and connectors are mentioned in Laoshu's article.
What, look at how the motherboard, network card, sound card, and graphics card on your computer are drawn, and get a feel for it.
These boards are masterpieces of masters.
Conceive a small product, follow the questions in Laoshu's article, find a book on protel99se, and start from each menu
Start from the minimum system of MCU->input->LED->RS232/RS422/RS485->solid-state relay
Start with schematic diagrams of devices, relays, etc., learn as you go, do it little by little, and when you are done, it is best to find an expert to look at it.
Find out where the problem is and make improvements repeatedly. Get a feel for it through such simulations.
I recommend Tiger Studio's Protel 99 series of 4 books, which are written in a step-by-step manner. Of course, they are not cheap; grit your teeth.
, you can buy a set together and take turns to watch it.
By the way, let me share my opinion on the development boards on the market. These development boards are certainly good, but you can only learn
Language cannot teach you how to draw schematics and PCB. When you actually do it, it will be fastest if you are guided by an expert.
I was taught by a friend, and it took me only half a day to learn it. At that time, it was Protel 3.16 under DOS
Version.
Find a company or enterprise and help them make a small product. You can get guidance from the company's experts and
Wouldn't it be great if you could earn some money? At this point, the cost of your development board and emulator comes out.
Picture->PCB->C51, and you have learned how to use microcontrollers.
Step 2: Master the circuit knowledge of the system
At this time, you need to have a comprehensive understanding of all electronic technology, mainly by reading magazines, BBS, websites
The technical articles on the Internet and the "Microcontroller Application Technology Encyclopedia" series edited by Mr. He Limin, which combines microcontrollers and
Its supporting circuits, input and output, communication, etc. have a comprehensive understanding. What is the goal?
Technical reserves. Know what problems can be solved by what methods and where the solutions may be found.
This will be very helpful for you to solve practical problems when you enter the workplace in the future. If you can really do this,
Then, you will definitely be better than the old comrades in the unit in the future.
When Lao Shu was in the state-owned research institute, he had nothing to do for a while. It was during that one or two years that he
I read the technical magazines of the institute, especially "Application of Electronic Technology", which laid a good foundation.
At this time, seize the opportunity to learn hardware design from experts. A faster way is to go to the manufacturer of industrial computers.
There, see how the industrial computer boards and conditioning boards are designed and what they use.
I once saw a device from abroad and asked around, but I still didn’t know what it was.
I saw that it was a solid-state relay. At this moment, all the knowledge about solid-state relays came to my mind.
At first glance, there is a huge supporting market.
This is how things are. If you don't know what it is used for, you will see it every day but ignore it.
People with aspirations are like this. They can slowly accumulate knowledge and strength in any situation. After all, a product,
It is not enough to just know the microcontroller, but it still requires a lot of peripheral circuits. According to Mr. He’s classification, forward,
A product can only be made through backward, human-machine, mutual channels, etc.
At this time, seize any opportunity to participate in a large-scale product development and do one thing in it.
Learn some elements of product development such as communication, collaboration, and interface.
Step 3: Diligence to Excellence
There are so many Chinese people, and everyone has an IQ of 100. Who is dumber than who? Why are you better than others?
With a good job and a good income, can you have a luxury car, fine wine and beautiful women? Lao Shu believes that there is no other way, just hard work.
Excited.
Study hard - everyone knows this truth, knowledge is money;
Hard work - If you want to make more money than others, you just need to work harder and earn more money.
High work efficiency. Others work 5×8 hours, you work 7×16 hours, if you double your work efficiency, you will soon
Did you make 5 times more money than others? There are two employees in Laoshu Company. They used to grow apples in their hometown but didn’t make any money.
I went to work at Lao Shu's company, on a piecework basis. When the work was busy, I got up at 8:00 in the morning and finished work at 12:00 at night.
At the end of the year, I made some money and went home happily. The old tree was also happy. The work that used to be done by a whole room of people was now done by two people.
If this is done, the company management will be easier and the employees will also make money.
The same is true for development. Of course, this requires your company to have this mechanism, a mechanism of more work, more pay.
There is no such thing now, do you want to do this?
I think it is necessary. On the one hand, do other people's work, practice your own skills, and improve your own abilities. On the other hand,
Only by working harder can you quickly improve your skills, achieve breakthroughs, and become proficient in your craft.
At least, there should be no problem with skilled trades.
It's like a pot of water. If you keep it on low heat, it will still be lukewarm after a long time. But if you turn on the high heat, it will soon boil over.
That's what I mean.
Look at Guo Jing in "The Legend of the Condor Heroes". He has no other skills, but he just practices foolishly. One day, he suddenly gets it, as if he has divine power.
Technology is like this. Once you break through the threshold, the road ahead is smooth. You need to be diligent, diligent, and diligent again.
When this day comes, your suffering will be over and your happiness will be rewarded.
Diligence also has another meaning, which is that God rewards diligence. In fact, everyone who sees a diligent person will give him a chance.
Yes, I feel happy to help such a person, and I feel at ease to put things in his hands.
Another meaning is to draw inferences from one instance to another. Knowledge requires a lot of references to compare, associate, extract and sublimate.
In other words, you may put in n times the effort of others, but you get n times more rewards.
The knowledge we have acquired is no longer a simple accumulation, it has undergone a qualitative change.
If you work hard and achieve results in this company, it doesn't matter if you are not treated fairly.
. Just change your environment, there will always be someone who will appreciate you. Besides, hard work always pays off.
Some people are used to complaining about their life, not having good parents, not having good teachers, not having good companions, not having good
environment, there is no good boss. These people need to read Zhou Ligong's article to see how Mr. Zhou
Growing.
Step 4: Communication and collaboration
There used to be some, but now there are fewer and fewer. By making a small product, you can live a worry-free life.
Step 5: Gain a Deeper Understanding of an Industry
Everyone needs to have a unique skill to survive in this world; especially if you are a reader of this forum,
;
Some people are born with a thousand charms, some people are born with golden voices, and some people have good parents; these are not enough
What's more, I don't have these talents?
When you master high-end technologies such as MCU, ARM, CPLD/FPGA, etc., it should be said that you will have no problem maintaining your health and making a living.
If you have mastered the basics of life, you can solve the basic problems of life; however, if you want to go a step further, you need to have a deep understanding of a certain industry.
Understanding and exploration of the
The engineers I know who live a life of luxury with BMWs by relying on their skills were not technically outstanding from the beginning.
The difference is not that his products are much better than others at the beginning, but that they are all very resilient people.
Seize the opportunities in a certain industry, work hard in a certain industry, and persevere, while others are doing other things.
Only he is still in this industry, taking his time, and after 5 years or more, he will gradually gain the recognition of people in the industry.
I was recognized, and I kept improving my products. I gradually opened up sales channels, and finally I was able to gain a foothold. When the opportunity came, I became rich.
A friend of mine achieved enlightenment through cultivation in this way.
There is a joke that says: The industry you just left develops the fastest. This is exactly the truth.
China is big and the market is huge. As long as you work hard, you will reap rewards.
Therefore, in China today, technicians still have opportunities, but in another 10 years, there may be no opportunities at all.
.
Do you need to work in multiple industries? As an individual, no. There is gold in every industry.
As far as the company is concerned, is it necessary? That depends on whether your company has talents in this area; it also depends on whether there is such
Otherwise, blindly expanding into multiple industries is unnecessary. What needs to be done is to at least
Rank among the top three in each industry.
You see, the original LOTUS notes were sold to IBM. Only 3 million copies were sold.
When the sales volume reaches 10 million copies (approximately). This is how products work. When you occupy the market, you will make profits.
A company does not need too many products, but it needs to sell a lot.
The output value is 1 million. The difference between one product and 10 products is huge. The R&D, service, and maintenance are very different.
Woolen cloth.
Like Gillette, it is just a small razor blade, but it has become such a big company. How comfortable it is.
Like GE, every industry is the leader in the industry, which is the result of 200 years of technological accumulation in capitalist society.
What needs to be done is that every small company has a product that is the most prominent. Start with a small product and become the best in the country.
Good, the best in Asia, the best in the world. That's it. China will be strong.
Only then will it be possible for a large company like GE to emerge and have the technological foundation to form such a large company.
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