Driving four 7-segment array by using multiplexing

This project uses a LIM-5652G 4 X 7-segment array which was rescued from an old satellite receiver. Any similar array will do as long as it is a common anode display. The array has the seven segments wired internally and supply output pins for the a, b, c, d, e f and g interconnected segments and four pins which select the segment required. As these supply the current for the diodes, they are driven via four BCY51 or similar transistors. The bases of the transistors are connected to the upper four digital output lines of the Velleman board.

As this leaves only four more lines and we require seven lines to drive the segments, I used a 7447 logic chip. This is a BCD to 7-segment decoder/driver. The four BCD input pins are connected to the lower four digital output pins of the Velleman board.

The arrangement is shown above. The only pin of the 7-segment display not connected drives the decimal points. A suggested PCB layout is shown on the right above. The PCB made from this negative was used for the circuit board in the photograph.

Programming the board

I have kept the program as simple as possible. It gives 5 choices. 1 to 4 select one of the four digits and count with it. Option 5 is the interesting bit. This counts from one to 9999 using multiplexing, i.e. switching between the four arrays so fast that the human eye is fooled into thinking it is looking at a continuous display. The work is done by lines 750 to 800.

750 DEFPROCscan(D1%,D2%,D3%,D4%) 760 SYS K8055_WriteAllDigital%,N%(D1%) OR Dis%(1) 770 SYS K8055_WriteAllDigital%,N%(D2%) OR Dis%(2) 780 SYS K8055_WriteAllDigital%,N%(D3%) OR Dis%(3) 790 SYS K8055_WriteAllDigital%,N%(D4%) OR Dis%(4) 800 ENDPROC

N%(D1%) to N%(D4%) supply the bit pattern for the number to be displayed. Dis%(1) to Dis%(4) contain the pattern that selects the current 7-segment array.

For instance, to write the number 9 to display 2 would return the binary numbers 1100, which is the pattern that writes the 9 and 01110000, which selects array 2. The two numbers are ORed, which makes 01111100 and this pattern is then sent to the output ports in rapid succession with the other three patterns. This scheme worked extremely well. With a K8055N board there is no flicker at all. The much slower K8055 shows a slight flicker, but the principle is well demonstrated - and this is all this project is designed to do.

As usual I supply a zip file with the BBC BASIC for Windows code and also a .exe file, should you not have BBC4W

K8055_7_seg_x4_1_1_N.zip

And here are the two files adapted for the K8061

K8061_7_seg_x4_1_0.zip

10 REM K8055_7-seg_x4 20 REM Multiplex four 7-segment displays 30 REM Jochen Lueg 40 REM http://roevalley.com 50 REM Limavady, May 2012 60 REM Version 1.0 70 80 90 ON ERROR PROCerror 100 PROCK8055_init 110 PROCinit 120 SYS K8055_CloseDevice%,Board% 130 SYS K8055_OpenDevice%,Board% 140 PROCscreen(700,280) 150 OFF 160 ON CLOSE PROCclose 170 *FONT Lucida Console,14,2 180 PRINT 190 PRINT " Select from the following:" 200 PRINT 210 PRINT " 1 . . . . . . . . Display 1 counts from 0 to 9" 220 PRINT " 2 . . . . . . . . Display 2 counts from 0 to 9" 230 PRINT " 3 . . . . . . . . Display 3 counts from 0 to 9" 240 PRINT " 4 . . . . . . . . Display 4 counts from 0 to 9" 250 PRINT " 5 . . . . . . . . Multiplex" 260 PRINT 270 PRINT " Q . . . . . . . . Return to this menu" 280 PRINT 290 REPEAT 300 REPEAT 310 Key$=INKEY$(0) 320 IF Key$="1" PROCcount_display(1) 330 IF Key$="2" PROCcount_display(2) 340 IF Key$="3" PROCcount_display(3) 350 IF Key$="4" PROCcount_display(4) 360 IF Key$="5" PROCmultiplex 370 UNTIL FALSE 380 PROCclose 390 END 400 410 420 430 DEFPROCcount_display(d%) 440 LOCAL Num% 450 Stop$="Run" 460 REPEAT 470 Num%=Dis%(d%)OR N%(Zahl%) 480 SYS K8055_WriteAllDigital%,Num% 490 Zahl%+=1:IF Zahl%=10 Zahl%=0 500 Key$=INKEY$(30) 510 IF ASC(Key$)<>-1 Stop$="Stop" 520 UNTIL Stop$="Stop" 530 ENDPROC 540 550 560 DEFPROCmultiplex 570 LOCAL A%,B%,C%,D% 580 FOR A%=0 TO 9 590 FOR B%=0 TO 9 600 FOR C%=0 TO 9 610 FOR D%=0 TO 9 620 TIME=0 630 REPEAT 640 PROCscan(D%,C%,B%,A%) 650 UNTIL TIME>5 660 IF INKEY(-17) SYS K8055_ClearAllDigital%:ENDPROC 670 NEXT 680 NEXT 690 NEXT 700 NEXT 710 SYS K8055_ClearAllDigital% 720 ENDPROC 730 740 750 DEFPROCscan(D1%,D2%,D3%,D4%) 760 SYS K8055_WriteAllDigital%,N%(D1%) OR Dis%(1) 770 SYS K8055_WriteAllDigital%,N%(D2%) OR Dis%(2) 780 SYS K8055_WriteAllDigital%,N%(D3%) OR Dis%(3) 790 SYS K8055_WriteAllDigital%,N%(D4%) OR Dis%(4) 800 ENDPROC 810 820 830 DEFPROCclose 840 SYS K8055_ClearAllDigital%,1 850 SYS K8055_CloseDevice%,1 860 SYS "FreeLibrary",K8055_Board% 870 QUIT 880 ENDPROC 890 900 910 DEFPROCscreen(ScreenWidth%,ScreenHeight%) 920 SYS "SetWindowPos",@hwnd%,0,0,0,ScreenWidth%,ScreenHeight%,6 930 VDU 26 940 COLOUR 128 950 CLS 960 COLOUR 15 970 ENDPROC 980 990 1000 DEFPROCerror 1010 PRINT REPORT$;" at line ";ERL : 1020 SYS K8055_ClearAllDigital%,1 1030 SYS K8055_ClearAllAnalog%,1 1040 SYS K8055_CloseDevice%,1 1050 SYS "FreeLibrary",K8055_Board% 1060 END 1070 ENDPROC 1080 1090 1100 DEFPROCinit 1110 Board%=0 1120 T%=-3 1130 Zahl%=0 1140 DIM N%(11) : REM Pattern for numerals 1150 N%(0)=%1111 1160 N%(1)=%1110 1170 N%(2)=%0111 1180 N%(3)=%0110 1190 N%(4)=%1011 1200 N%(5)=%1010 1210 N%(6)=%0011 1220 N%(7)=%0010 1230 N%(8)=%1101 1240 N%(9)=%1100 1250 N%(10)=%0000 : REM segments All OFF 1260 1270 DIM Dis%(4) 1280 Dis%(0)=%11110000 : REM All four arrays OFF 1290 Dis%(1)=%01110000 1300 Dis%(2)=%10110000 1310 Dis%(3)=%11100000 1320 Dis%(4)=%11010000 1330 ENDPROC 1340 1350 1360 DEFPROCK8055_init 1370 REM Typing errors in routine name do not generate an error message - they just hang up the program. 1380 REM These are all the system calls in the order found in the manual 1390 SYS"LoadLibrary","K8055D.dll" TO K8055_Board% 1400 SYS"GetProcAddress",K8055_Board%,"OpenDevice" TO K8055_OpenDevice% 1410 SYS"GetProcAddress",K8055_Board%,"CloseDevice" TO K8055_CloseDevice% 1420 SYS"GetProcAddress",K8055_Board%,"ReadAnalogChannel" TO K8055_ReadAnalogChannel% 1430 SYS"GetProcAddress",K8055_Board%,"ReadAllAnalog" TO K8055_ReadAllAnalog% 1440 SYS"GetProcAddress",K8055_Board%,"OutputAnalogChannel" TO K8055_OutputAnalogChannel% 1450 SYS"GetProcAddress",K8055_Board%,"OutputAllAnalog" TO K8055_OutputAllAnalog% 1460 SYS"GetProcAddress",K8055_Board%,"ClearAnalogChannel" TO K8055_ClearAnalogChannel% 1470 SYS"GetProcAddress",K8055_Board%,"ClearAllAnalog" TO K8055_ClearAllAnalog% 1480 SYS"GetProcAddress",K8055_Board%,"SetAnalogChannel" TO K8055_SetAnalogChannel% 1490 SYS"GetProcAddress",K8055_Board%,"SetAllAnalog" TO K8055_SetAllAnalog% 1500 SYS"GetProcAddress",K8055_Board%,"WriteAllDigital" TO K8055_WriteAllDigital% 1510 SYS"GetProcAddress",K8055_Board%,"ClearDigitalChannel" TO K8055_ClearDigitalChannel% 1520 SYS"GetProcAddress",K8055_Board%,"ClearAllDigital" TO K8055_ClearAllDigital% 1530 SYS"GetProcAddress",K8055_Board%,"SetDigitalChannel" TO K8055_SetDigitalChannel% 1540 SYS"GetProcAddress",K8055_Board%,"SetAllDigital" TO K8055_SetAllDigital% 1550 SYS"GetProcAddress",K8055_Board%,"ReadDigitalChannel" TO K8055_ReadDigitalChannel% 1560 SYS"GetProcAddress",K8055_Board%,"ReadAllDigital" TO K8055_ReadAllDigital% 1570 SYS"GetProcAddress",K8055_Board%,"ResetCounter" TO K8055_ResetCounter% 1580 SYS"GetProcAddress",K8055_Board%,"ReadCounter" TO K8055_ReadCounter% 1590 SYS"GetProcAddress",K8055_Board%,"SedtCounterDebouceTime" TO K8055_SetCounterDebounceTime% 1600 ENDPROC