Design of traffic light control system based on MCU

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send out ： SCM traffic lights
Access to the source code + The report + Schematic diagram and simulation

1、 With a single chip microcomputer STC89C52 Design a traffic light system , And use digital tube to display time ,LED Indicate passage .
2、 use 74HC245 To drive 4 A digital tube , Make the nixie tube appear brighter during the day .
3、 Key function ： The yellow light is always on （ Late night mode ）、 No way 、 East West traffic 、 North south traffic 、 Time plus 、 Less time 、 Switch 、 determine .

Overall block diagram of system design

Principle description of each module
Minimum system AT89C52 modular
AT89C52 It's a low voltage , High performance CMOS 8 Bit MCU , Film inclusion 8k bytes Rewritable Flash Read only program memory and 256 bytes Random access data memory （RAM）, The device adopts ATMEL The company's high density 、 Non volatile storage technology production , Compatible standards MCS-51 Command system , Built in universal 8 Bit CPU and Flash Storage unit ,AT89C52 SCM is widely used in electronic industry .
52 Principle description of minimum system of single chip microcomputer ：
4.5V Power Supply ： Power the system .
Crystal oscillator ： Provide pulses for the operation of single chip microcomputer .
EA Connected to high level ： Indicates that the program downloaded from the internal program memory is run .

Description of main pins ：
VCC（40 foot ）： Supply voltage
GND（20 foot ）： Grounding .
RST： Reset input .
/EA/VPP(31 foot )： When /EA Keep the battery low , Then during this period, the external program memory （0000H-FFFFH）, Whether or not there is internal program memory . Only use external memory , Otherwise, the on-chip program memory is selected after the MCU is powered on or reset .
XTAL1（19 foot ）： The input of the reverse oscillation amplifier and the input of the internal clock working circuit .
XTAL2(18 foot )： Output from the reverse oscillator .

74HC245 Chip module
74HC245 It's a high-speed CMOS device ,74HC245 Pin compatible with low power Schottky TTL（LSTTL） series . 74HC245 The eight way transceiver has positive phase tri state bus compatible output in both sending and receiving directions .74HC245 The output enable end of （OE） For easy cascading , And send / The receiver （DIR） Used to control direction .OE Control output , The bus is effectively isolated .） Output .
Pin instructions ：

（1） The first 1 foot DIR, For input / output port conversion ,DIR=“1” High level signal is generated by “A” End input “B” End output ,DIR=“0” The low level signal is generated by “B” End input “A” End output .
（2） The first 2~9 foot “A” Signal input and output terminals ,A0=B0…A7=B7,A0 And B0 It's a group. , If DIR=“1”OE=“0” be A1 Input B1 Output , Other similar . If DIR=“0”OE=“0” be B1 Input A1 Output , Other similar .
（3） The first 11~18 foot “B” Signal input and output terminals , Function and “A” The same , No more description .
（4） The first 19 foot OE, Enable end , If the foot is “1”A/B The signal at the terminal will not be connected , Only for “0” when A/B End is enabled , This foot also acts as a switch .
（5） The first 10 foot GND, Power ground .
（6） The first 20 foot VCC, Positive pole of power supply .

Display module functions
The display modules are code tube display and LED Show , The digital tube countdown display can remind the driver of the time when the signal light color changes 、 stay “ stop it ” and “ adopt ” Choose between the two . Drivers and pedestrians are generally willing to choose the signal control mode with countdown display , And think that the intersection with countdown display is safer . Countdown display is a method used to reduce the driver's complex judgment at the critical moment of signal color change , It can remind the driver of the time when the light color changes , Help the driver in “ stop it ” and “ adopt ” Choose between the two . Through the combination of two displays , This design is more reasonable and reliable . Here's the picture 3-4 Shown .

Control button module
This system requires few key controls , And I／0 Enough mouth , Independent type can be adopted directly . Press the key to set the running state of the system , The forbidden status is displayed on the nixie tube “00”, All the red lights are on ; The reset button can reset the whole system ; East West traffic is the green light in the east-west direction , The red light in the north-south direction is on ; The green light on the north-south direction is on when you travel from north to South , The red light in the east-west direction is on ; Time addition and subtraction can set the time of passing and waiting for passing ; The switch button can switch the direction and time of addition and subtraction . Through the control of the security check module , Make the whole system flexible , practical . Here's the picture 3-5 Shown .

Description of the general schematic diagram of the system
When on 4.5v After power supply , Press the power switch , North south direction nixie tube display “25”. The nixie tube begins to count down , To 5 seconds , Yellow light and buzzer sound 5 Next , The red, green and yellow lights will be switched . Key 1 function 、 Key 2 The yellow light is always on （ Late night mode ）、 Key 3 The red light is always on （ Emergency mode ）、 Key 4 Reset 、 Key 5 East West traffic 、 Key 6 North south traffic 、 Key 7 Time plus 、 Key 8 Less time 、 Key 9 stop it . The general schematic diagram of the system is shown in Annex 1.