GorbaDisplay
| Project GorbaDisplay | |
|---|---|
| File:Whyunopicture.jpg | |
| Public transport LED display | |
| Status | Initializing |
| Contact | bertrik, User:Eloy |
| Last Update | 2023-08-02 |
Introduction
This project is about reverse engineering a former public transport LED display. It consists of Z panels of each X * 16 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
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 controlled simultaneously.
The display board contains the following integrated cicruits:
- 74HC541, an octal buffer/line driver, probably buffers all signals coming in from the 14-pin connector to the rest of the electronic on the display board
- 74HC238, a 3-to-8 line decoder/demultiplexer, probably selects which row is currently being lit up
- group of 4x IRF7425, power MOSFET, probably for driving a row of LEDs with
- a whole bunch of TPIC6C596, 8-bit shift register, probably drives the columns inside one row of LEDs
The demultiplexer handles only 3 bits, enough for 8 rows. 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:
| Pin | Name | Remark |
|---|---|---|
| 1 | ? | Power or ground |
| 2 | ? | Power or ground |
| 3 | ? | |
| 4 | ? | |
| 5 | ? | A1 of row multiplexer |
| 6 | ? | A2 of row multiplexer |
| 7 | ? | |
| 8 | ? | |
| 9 | ? | |
| 10 | ? | A0 of row multiplexer |
| 11 | ? | |
| 12 | ? | SRCK of column shift register |
| 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
- ground pin