GorbaDisplay: Difference between revisions

From RevSpace
Jump to navigation Jump to search
Line 55: Line 55:
* 13 - power or ground
* 13 - power or ground
* 14 - power or ground
* 14 - power or ground
There are possibly pins for:
* row select, bit 0
* row select, bit 1
* row select, bit 2
* row select, bit 3
* row-enable
* shift register data
* shift-register clear
* shift-register data
* analog LDR value
* remote control input
* power pin
* power pin
* ground pin
* ground pin


== Software ==
== Software ==

Revision as of 21:58, 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

The demultiplexer handles only 3 bits, perhaps there are two of them to handle 16 rows: one for the top 8 rows and one for the bottom 8 rows.

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

There are possibly pins for:

  • row select, bit 0
  • row select, bit 1
  • row select, bit 2
  • row select, bit 3
  • row-enable
  • shift register data
  • shift-register clear
  • shift-register data
  • analog LDR value
  • remote control input
  • power pin
  • power pin
  • ground pin
  • ground pin

Software