Train Station Display

In upstairs metalworking there is a train station display - photos on flickr

Parts

LED Module

Each LED module contains an 8x7 grid of LEDs.

LED Module Backplane

Each backplane holds 8 LED modules. There is a 14 pin IDC header on the right of each board, these go to a CD74HCT541E octal buffer.

Input IDC header (as viewed from the solder side)

     +-----+
GND -| o o |- A0
GND -| o o |- A1
GND -| o o |- A2
?   -| o o |- A3
GND -| o o |- A4
 A7 -| o o |- A5
GND -| o o |- A6
     +-----+

CD74HCT541E

    V O 
    c E Y Y Y Y Y Y Y Y     <---- outputs
    c 2 0 1 2 3 4 5 6 7  
  +---------------------+
  |>   CD74HCT541E      |
  +---------------------+
    O A A A A A A A A G
    E 0 1 2 3 4 5 6 7 N     <--- inputs
    1                 D

Some of the output lines from the line driver go to the shift registers, while others go to a BCD decoder. Each LED Module has two shift registers which are both updated on each clock pulse.

CD74HCT541E Outputs

Y0 - All shift registers, CLOCK
Y1 - Bottom shift register of LED Module 0, Data In
Y2 - BCD Decoder "A"
Y3 - BCD Decoder "B"
Y4 - BCD Decoder "C"
Y5 - BCD Decoder "D"
Y6 - All shift registers, STROBE
Y7 - Top shift register of LED Module 1, Data In

The shift registers used are CMOS MIC5821BN

MIC5821BN

     O O O O O O O O
     1 2 3 4 5 6 7 8
   +-----------------+
   |> MIC5821BN      |
   +-----------------+
     C S V V S S O V
     L i s d o T E e
     K   s d   B   e

Vss, OE and Vee are all tied to ground.
Si is serial in and connects to either Y1 or Y2 of the line driver, or to So of the previous shift register.

(Need to verify) The BCD decoder (CD4028BCN) is used to turn on/off each LED Module's MOSFET (IRF540) via a source driver UDN2981A.

    V
    d
    d 3 1 B C D A 8
  +-----------------+
  |>  CD4028BCN     |
  +-----------------+
    4 2 0 7 9 5 6 V
                  s
                  s

                    G
                    N
    . . . . . . . . D 
  +-------------------+
  |>  UDN2981A        |
  +-------------------+
   . . . . . . . . V
                   s

Backplane Frame

Each LED Module Backplane is arranged on the backplane frame.

The backplanes are grouped into two. The first group drives 6x8 LED Module backplanes (total of 2688 LEDs) and the second drives 4x8 LED Module backplanes (1792 LEDs). In total there are 4480 LEDs per side.

+------------------+------------------+------------------+
|  A2              |  A1              |   A0             |  <--- Input
+------------------+------------------+------------------+
|  A5              |  A4              |   A3             |
+------------------+------------------+------------------+
|  B2              |  B1              |   B0             |  <--- Input
+------------------+------------------+------------------+
                   |  B3              |
                   +------------------+