LED displays are widely used in industrial and mining enterprises , schools , shopping malls, stores , public places etc. graphic displaying , advertising , information dissemination . In this paper,design a kind of display
consists of four 16 × 16 dot of LED modules, smooth mobile display any a number of text or graphic marks by the microcontroller as controller , the circuit cascades extension realizing display by any number of consisting of 16 × 16 dot LED modules .
1)the circuit design
It is controller of AT89C51 microcontroller in control circuit , display consists of four 16 × 16 dot LED modules, each consists of four 8 × 8 dot LED module, the user can increase any number of 16 × 16 dot LED module according to need of extension.Structure 8 × 8 dot LED module shown as Figure 1 , a total of 8 rows and 8 columns , each light-emitting diodes placed on the intersection of the row and column lines , a total of 64 light-emitting diodes. Corresponding LED light When A column is high level, and a row is low level .
SCM P3.0 pin is connected to series and is shifted serial data inputs of register 74LS164 (U10), eight cascades
74LS164 (U10 ~ U17), P3.1 pin is connected to pulse input of eight clocks 74LSl64 ; eight 74LS164 is respectively connected to eight latch 74LS373 (U18 ~ U25), eight latches data output is connected with row lines of four 16 × 16 dot matrix LED module , each row lines of 16 × 16 dot matrix LED module are independently controlled . P1.O is connected with pulse input of eight clocks 74LS164 (U2 ~ U9) , P1.1 is connected with serial data input U2, U4, U6, U8,every two 74LSl64 (U2 and U3, U4 and U5, U6 and U7, U8 and U9) is cascaded ; parallel data output U2 ~ U9 is connected with 64 column lines of four 16 × 16 dot matrix LED module. P1.2 latch is connected to 0 termination 74LSl64, P1.3 is connected to control termination of latch .
2) the working theory
The circuit uses a serial communication port working on Mode 0 , at the meantime apply P1.O and P1.1 simulate serial output , to realize a character smooth moving display on LED mobile display . Since the LED module is 16 × 16 dot matrix, so the character matrix is 16 × 16 dot,that is to say each character consist of 32 bytes or 16 character of data, each word data determines matter of each column LED light. 16 × 16 dot matrix character data is obtained from withdraw software of character dot matrix .
At first, MCU P1.1 serial output a binary "1" ,loading a high level through 4 groups of 74LSl64 to four 16 × 16 dot matrix LED module, following output a first row of line data of four 16 × 16 dot matrix LED module, i.e. row data of columns Y1, Y17, Y33, Y49, sending to LED display row line after 74LS373 latch , by this time corresponding LED of first column of each LED module lights up.
Rows of data every column is a character data , four of four character data, first byte of every character data is different of 32 in address of character matrix data sheet ,in where each LED module display first column of every character . Then P1.1 serial output a binary "0" , loading a high level after shift by 4 groups of 74LSl64 to second column four 16 × 16 dot matrix LED module,then outputing by P3.O serial rows data of second column of four 16 x 16 dot matrix LED modules , namely row data of column Y2, Y18, Y34, Y50,sending to row line of LED display, by this time corresponding LED of second column of each LED module lights up, namely display second column of every character.circulation so,lighting up in turn corresponding LED till 16th column of every LED module,namely display in turn respectful column of every character.As long as alternate display time of every column is
appropriate ,look like 16 column LED light at the same time by taking advantage of persistence characteristics of human eye's vision,namely entire characters display simultaneously. Then sequentially scanned display from first column to the sixteen , and so many times to ensure the displayed characters have sufficient brightness.
To realize the effect of the smooth movement of the characters, after a certain time of realized four characters static display above,beginning to scan display from second column data of every character in the first column of every LED module when the scan again.the first two starts scanning each character display , ie first LED module display second column of first character ,third column ...... ,16th column and the first column of second character ,
second LED module display second column of second character ,third column ...... ,16th column and the first column of third character, second column......when scanning third time,beginning to scan display from third column data of every character in the first column of every LED module,ie first LED module display third column of first character ,forth column ...... 16th column and the third column of second character,forth column......, second LED module display third column of first character ,forth column ...... ,16th column and the first column of third character, second column...... so realizing a smooth movement of the character display .
3)Program design
According to circuit design and working theory above , mapping out flow diagram of control program of the circuit . Then written control programs according to flow diagram, creating object code file with Wave or Keil software debugging and after pass.
4)Circuit simulation
Adding object code file to microcontroller of simulated diagram with Proteus software drawn LED display circuit control , simulation run , run results .
5) Conclusion
The LED display circuit control uses microcontroller as controller, applying the serial shift output, realizing a row of character display of smooth movement, should be added relevant drive circuit in practical application. This circuit can be extented realizing display control by any number of consisting of 16 × 16 dot LED display module. The practical application shows that the circuit is stable and reliable , and good results.
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