Part I: hardware knowledge
1. Digital signal
1. TTL and TTL signal with buffer
2. RS232 and definition
3. RS485/422 (balanced signal)
4. Dry contact signal
2. Analog signal video. Balanced signal
3. Chip
1, package
2, 747
3, 744
4, 74
5, 74LS573
6, ULN23
7, 74LS244
. 238
11, CPLD(EPM7128)
12, 1161
13, max691
14, max485/75176
15, mc1489
16, mc1488
17. Package
2, resistance: power consumption and capacitance
3, capacitance
1) monolithic capacitor
2) ceramic capacitor
3) electrolytic capacitor
4, inductance
5, power conversion module
6, terminal
7, LED light-emitting tube. Buzzer
5. Minimum system of single chip microcomputer
1, single chip microcomputer
2, watchdog and power-on reset circuit
3, crystal oscillator and ceramic capacitor
6. Serial interface chip
1, eeprom
2, serial I/O interface chip
3, serial AD and DA
4 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. Design idea
1. Power supply: voltage and current
2. Interface: serial port, switch input and switch output
3. Switch signal output conditioning
1) TTL-> Relay
2) TTL->; Relay (reverse logic)
3) TTL->; Solid state relay
4) TTL->; LED(8 characters)
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 capacity
6, consideration of becoming a product:
1) circuit board shape: size, shape, connector and space volume
2) modular design of circuit board
3) cost analysis
4) redundancy of devices
1. Power consumption of resistors
.
2. how to reduce the cost? Choose devices with cheap functions
X. Thinking questions
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. Secondary dimming
4. Design a 33-bit 1 "8-character display board
1) Power supply: DC5V
2) Interface: RS232
3) 3 rows of 11-bit 8-characters, divided into 4, 3 and 4 groups. There is a space between lines
4) Minimum system of single chip microcomputer
5) Decoding logic
6) Display driver and driver
5. Design an interface board of PCL725 and MOXA C168P
1) Power supply: DB37
2) Interface: PCL725/MOXA 8 RS232
. Hole
2. MOXA C168P, DB62 bend
3) Switch output signal conditioning: 6 solid-state relays and 8 relays, which can be controlled and driven by any signal. Interface: solid-state relay 5.8 stands upright, relay 3.81 stands upright
4) Switch input conditioning: dry contact closure is 1 or . Interface: 3.81 vertical
5) RS232 conditioning:
1. LED indication
2. The first four channels are all RS232 signals, and the last four channels only need TX, RX and
3. No photoelectric isolation is needed
4. Interface form: DB9 (needle) vertical
Part II: Software knowledge.
why do you need to master this knowledge?
in fact, an electronic engineer just puts a bunch of devices together, injects ideas (programs), and completes the functions that the original devices can't accomplish when they are separated, so as to make a finished product. The higher the required skills, the more complex the functions, the lower the cost, and the greater the demand for the corresponding things in the market, the more successful it will be. This is the value of electronic engineers themselves. From cost to product sale, the difference between them is the pursuit of enterprises. As the boss of an enterprise, I look for such an application in the
market; For electronic engineers, it is to complete the requirements or applications put forward by the boss in the shortest
time according to certain conception principles (lowest cost, highest reliability, smallest circuit board, most powerful function, etc.). The shortest time is directly related to the proficiency, work efficiency and working hours of electronic engineers. This is the value of electronic engineers.
the electronic product is abstracted into a hardware model, which consists of the following components:
1) input
2) processing core
3) output
basically, the input has the following possibilities:
1) keyboard
2) serial interface (RS232/485/can bus/ Ethernet/. Dry contact)
4) analog (4~2ma, ~1ma, ~5V (balanced and unbalanced signals)
output basically consists of the following components:
1) serial interface (RS232/485/can bus/ Ethernet /USB)
2) switch value (TTL, USB). ~1ma, ~5V (balanced and unbalanced signals)
4) LED display: LED, splay
5) LCD
6) Buzzer
Processing core mainly includes:
1) 8-bit single chip microcomputer, mainly 51 series
2) 32-bit arm single chip microcomputer. You can also add an operating system to arm. The program is
reliable and easy to write.
Recently, Samsung's arm is sought after, and its price is cheap. There are also interfaces between Ethernet and USB, and the development system in Zhou Ligong is also cheap. As a product for learning ARM, it should be the best. As an industrial control, whether it is suitable or not, there are different views and disputes among netizens. A product for outdoor use < P > developed by our company using atmel ARM91 series has been used outdoors in Beijing without any ventilation and heating measures. It has been running well since May last year. There has been a successful application case.
But for beginners, we should start with 51. On the one hand, 51 is still an entry-level chip, and it is better to practice
as a beginner. You can go through the above concepts. Many special single-chip computers also add some I/O, A/D and D/A on the basis of 51 cores. It also lays a foundation for learning higher-level single-chip microcomputer and ARM in the future.
Besides, which boss will put the development of ARM level in the hands of a novice who has not even learned 51?
It is unnecessary to do complicated parallel expansion on 51, for example, expanding I/O port and A/D, D/A, etc.
You can directly buy a single chip microcomputer with A/D and D/A; Or directly use ARM, which has many I/O ports. You can make
chips with I2C interface, expand I/O port and A/D, D/A, and SPI interface to expand LED display, such as
chips such as p>MAX7219.
There are some examples of parallel expansion in some older books on the market, such as RAM, EPROM, A/D,
D/A, etc. I don't think it's necessary to read them, just know that there are these things in history.
these knowledge are the essential elements of all products. Therefore, it is necessary to learn and then apply it concretely.
tell a short story: the exposure of a wild man.
once upon a time, there was a farmer who took a rest and basked in the sun after working in winter. It's so comfortable
He thought, I would like to dedicate this comfortable enjoyment to the king so that he can enjoy it.
So he went to the palace excitedly and dedicated his valuable experience to the king.
I'm like this farmer now, and I'm giving you my valuable experience. I hope you can give us more valuable opinions
; It's okay to pat a brick, but it doesn't matter if you scold me, hehe, whatever.
Lesson 1: 51 Minimum System of Single Chip Microcomputer
In fact, the core peripheral circuit of 51 Single Chip Microcomputer is very simple, with a single chip microcomputer+a watchdog+a crystal oscillator
+2 disk capacitors;
1. Single-chip microcomputer: 89C51 series of atmel, 78E52 series of winbond and philips series, all with little difference
; Now some of them have ISPs (downloaded online), which is better to use;
2. Watchdogs: There are many kinds, among which max691/ca1161 and DS1832 are commonly used, depending on personal habits,
chip working voltage and packaging. Max series and DS series, as well as IMP company's, have many kinds, generally only need to have the most basic functions. Originally, I used max691, but max691 was more expensive, because it had the function of battery switching. Later, when I newly designed the circuit board, I adopted ca1161.
In the circuit design of a long time ago, people may still use the power-on reset circuit made of a resistor and a capacitor. However, such a reset circuit is unreliable. Why is it unreliable? Articles devoted to reset circuits can be found on the Internet. More importantly, the 51-series single-chip microcomputer is more susceptible to interference; It's impossible without a watchdog circuit. When the program flies, it can't come back and die there.
The conventional practice is to buy a special watchdog circuit to complete the functions of reset circuit and watchdog circuit.
the information of these chips is easy to find on the internet, and Baidu search is usually enough; When you see the word
in PDF, click Download; It is also the best to download using flashget Flashget;
These materials are usually in pdf format, so you need a pdf reader.
Baidu website:
flashget download website:
PDF reader download website:
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-ROMs, and there is no need to look everywhere.
The anti-interference ability of single chip microcomputer and single chip microcomputer is different. If your product is working in a noisy environment < P >, you can try to choose different brands of single-chip microcomputer. It turned out that I was working in a photoelectric institute as the control < P > system part of YAG laser therapy machine. When the power supply of the pulse laser machine was discharged, the energy was very large. After taking all conceivable measures such as < P > photoelectric isolation, it still couldn't work. Later, intel's 831 was selected, and it was fine. Whispered
: At that time, philips' single-chip computer had the worst anti-interference performance, which may be related to the fact that Philips was mainly used in civil
fields. I don't know what's going on now. Let me know if anyone knows.
The I/O line of single chip microcomputer is the place where interference is most likely to be introduced; In the case of serious interference, it is necessary to photoelectric isolate all
ports.
3. crystal oscillator: generally, 11.592M is selected, because 96 baud rate and 192 baud rate can be accurately obtained; Also
you can use 36.864M, which is 2 times as high as 1.8432M Seeing that other people's circuit boards have used it, I didn't
use it. These two kinds of crystal oscillators are easy to buy, and the price is the same as that of 12M. It is said in the book that a 12M crystal oscillator can also get a baud rate of
96. However, when it is actually used, it will make an error every once in a while, which is strange, as if the accumulated error is < P >.
Even if your MCU system doesn't use Rs232 interface, you can make an RS232, keep it for testing, or
reserve it in advance, etc. There is no harm. Unless the port line of your single chip microcomputer system is not enough.
4. Disk capacitance: 22pf～3pf. What crystal oscillation frequency can be found in some books?