About the article

Modular Dot Matrix Display

PC interface to the COM port

Modular Dot Matrix Display
Moving signs are a common enough sight today but off-the-shelf units are invariably expensive and somewhat inflexible. The six-character module described in this article can be cascaded up to 16 modules long and has a character set that can be customised to suit your application.The dot matrix moving sign module presented here has a six character display area. A maximum of 16 of these modules can be cascaded together to produce a 96-character display. The PCB layout for the module can accommodate 5×7-Matrix displays with a distance between the rows of pins of 33.0 mm (30 mm character height) but larger or smaller displays may also be fitted by using adapter boards, if the LED matrix is electrically compatible, of course.The big advantage of building this moving sign yourself is that the cost of the finished article is much less than that of a ready-built unit. Most of the ICs used in the design are widely available and relatively cheap. The passive components are all standard and an AT89C2051 with Flash-memory is not the most expensive microcontroller. The main item from a cost point of view is the type of LED matrix displays that are used.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1-R5 = 10kOhm
R6, R38-R44 = 2kOhm 2
R7 = 33kOhm
R8-R37 = 330Ohm
C1,C2 = 18pF
C3,C4 = 10µ F 16V radial
C5,C6,C7 = 100nF
D1 = 1N4148
LD1-LD6 = TC12-11SRWA (Electromail) or TC12-11HWA (Kingbright, Conrad Electronics)
T1 = BC547
T2...T8 = BC640
IC1 = 89C2051-24PC, programmed, order code 010021-41
IC2 = 74LS138
IC3-IC8 = 74LS164
S1 = 4-way DIP switch
X1 = 22.1184MHz quartz crystal
PCB, order code 010021-1
Disk, order code 010021-11
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