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=== 14-pin connector ===
=== 14-pin connector ===
My guess for the pinout so far is:
My guess for the pinout so far is:
*  1 - power or ground
*  2 - power or ground
*  3 - ?
*  4 - ?
*  5 - A1 of multiplexer
*  6 - A2 of multiplexer
*  7 - ?
*  8 - ?
*  9 - ?
* 10 - A0 of multiplexer
* 11 - ?
* 12 - SRCK, data clock
* 13 - power or ground
* 14 - power or ground


== Software ==
== Software ==

Revision as of 21:42, 1 August 2023

Project GorbaDisplay
File:Whyunopicture.jpg
Public transport LED display
Status Initializing
Contact bertrik, User:Eloy
Last Update 2023-08-01

Introduction

This project is about reverse engineering a former public transport LED display. It consists of Z panels of each X*Y LEDs. Each panel has 16 amber LEDs vertically.

The plan is to make the display fully addressable as a bitmap display over a network connection, preferably with individually controllable brightness.

Hardware

14-pin header + chips

This thing consists of two main parts:

  • a control board, with logic to receive (for example) text messages over a serial connection and convert them to a bitmap display on the display board
  • a display board, with logic to light up each LED

Between them is a 14-pin connector, probably carrying the low-level LED control signals.

The display board consists of several (4?) panels of LEDs.

It has a light sensor to sense the ambient light level.

Theory of operation

My guess this is probably another row-multiplexed display. The display can light up one row at a time. By quickly lighting up each row in succession, the illusion to a human observer is that all LEDs are on simultaneously.

The display board contains the followings integrated cicruits:

  • 74HC541, an octal buffer/line driver, probably buffers all signals coming in from the 14-pin connector to the rest of the electroncis
  • 74HC238, a 3-to-8 line decoder/demultiplexer, probably selects which row is currently being lit up
  • group of 4x IRF7425, power MOSFET, probably drives a row of LEDs
  • a whole bunch of TPIC6C596, 8-bit shift register, probably drives the columns inside one row of LEDs

14-pin connector

My guess for the pinout so far is:

  • 1 - power or ground
  • 2 - power or ground
  • 3 - ?
  • 4 - ?
  • 5 - A1 of multiplexer
  • 6 - A2 of multiplexer
  • 7 - ?
  • 8 - ?
  • 9 - ?
  • 10 - A0 of multiplexer
  • 11 - ?
  • 12 - SRCK, data clock
  • 13 - power or ground
  • 14 - power or ground

Software