HDSP clock with SCD5583 display

Here is another interesting "intelligent" LED matrix display, whose name actually makes some sense (unlike HDSP-2354, among many others): SCD5583A. I reckon it means: "Serial Character Display with 5x5x8 dot matrix". 3 is the code for green (0 for red, 1 for yellow).
This display is now obsolete (replaced by touch screens in avionics, the industry for which it was designed), but it is still available on ebay for a reasonable price (except for incredibly high shipping cost).

Compared to other intelligent displays like the above-mentioned HDSP-2534 employed by the HDSP clock (hence the bland unimaginative name), SCD558X does not have an internally-defined font and requires the user to provide one. This makes it a little more complicated to use, but also allows for more flexibility, making it truly international (non-English character set). Even more, each pixel can be addressed individually, like a graphical 5x40 LED matrix.
The fact that is serial means fewer pins are required for interfacing (3 control pins in this case) and less driving circuitry (no need for the external shift register).

The photo below shows the display connected to an Arduino and running the HDSP sketch adapted for SCD5833.

Practically, the HDSP sketch uses only one function to write to display, aptly called "writeDisplay()", that needs to be re-written. The support for SCD5583 is provided by the class SCD5583, shown below (header + cpp files, compiled with Arduino IDE 1.8.13).

#ifndef _SCD5583_H_
#define _SCD5583_H_

#include  "Arduino.h"

class SCD5583
{
  public:
    SCD5583(byte loadPin, byte dataPin, byte clkPin);
    void clearMatrix();
    void setBrightness(byte b);
    void writeLine(char text[9]);

  private:
    void _sendData(byte data);
    void _getCharDefinition(byte* rows, char c);
    void _selectIndex(byte position);

    byte _loadPin;
    byte _dataPin;
    byte _clkPin;
};

#endif // _SCD5583_H_

-----------------------------------------------

#include "SCD5583.h"
#include "font5x5.h"

#define MAX_CHARS 8   // set to 10 for SCD5510X (10 digits) or to 4 for SCD554X (4 digits);
#define NUM_ROWS  5

SCD5583::SCD5583(byte loadPin, byte dataPin, byte clkPin)
{
  pinMode(loadPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(clkPin, OUTPUT);
  _loadPin = loadPin;
  _dataPin = dataPin;
  _clkPin  = clkPin;
  clearMatrix();
//  setBrightness(0);
}

void SCD5583::clearMatrix()
{
  _sendData(B11000000);
}

void SCD5583::setBrightness(byte b)
{
  if (b > 0 && b < 7)
  {
     _sendData(B11110000 + b);
  }
}

void SCD5583::_selectIndex(byte position)
{
   _sendData(B10100000 + position);
}

void SCD5583::_sendData(byte data)
{
  byte mask = 1;
  digitalWrite(_loadPin, LOW);
  digitalWrite(_clkPin,  LOW);
  for (byte i = 0; i < 8; i++)
  {
    digitalWrite(_dataPin, mask & data? HIGH : LOW);
    digitalWrite(_clkPin, HIGH);
//  delay(10);
    digitalWrite(_clkPin, LOW);
    mask = mask*2;
  }
  digitalWrite(_loadPin, HIGH);
}

void SCD5583::_getCharDefinition(byte* rows, char c)
{
  for (byte i = 0; i < NUM_ROWS; i++)
  {
    rows[i] = font5x5[((c- 0x20) * NUM_ROWS) + i];
  }
}

void SCD5583::writeLine(char* text)
{
  byte rows[NUM_ROWS];
  for (int i = 0; i < MAX_CHARS; i++)
  {
    _selectIndex(i);
    _getCharDefinition(rows, text[i]);
    for (int r = 0; r < NUM_ROWS; r++)
    {
      _sendData(rows[r]);
    }
  }
}

As mentioned previously, the font must be provided too (content of file "font5x5.h" shown below):

#ifndef _FONT5X5_H_
#define _FONT5X5_H_

// ascii characters 0x41-0x7a (32-127);
static unsigned char font5x5[] =
{
  0x00, 0x20, 0x40, 0x60, 0x80, // space
  0x04, 0x24, 0x44, 0x60, 0x84, // !
  0x0A, 0x2A, 0x40, 0x60, 0x80, // "
  0x0A, 0x3F, 0x4A, 0x7F, 0x8A, // #
  0x0F, 0x34, 0x4E, 0x65, 0x9E, // $
  0x19, 0x3A, 0x44, 0x6B, 0x93, // %
  0x08, 0x34, 0x4D, 0x72, 0x8D, // &
  0x04, 0x24, 0x40, 0x60, 0x80, // '
  0x02, 0x24, 0x44, 0x64, 0x82, // (
  0x08, 0x24, 0x44, 0x64, 0x88, // )
  0x15, 0x2E, 0x5F, 0x6E, 0x95, // *
  0x04, 0x24, 0x5F, 0x64, 0x84, // +
  0x00, 0x20, 0x40, 0x64, 0x84, // ,
  0x00, 0x20, 0x4E, 0x60, 0x80, // -
  0x00, 0x20, 0x40, 0x60, 0x84, // .
  0x01, 0x22, 0x44, 0x68, 0x90, // /
  0x0E, 0x33, 0x55, 0x79, 0x8E, // 0
  0x04, 0x2C, 0x44, 0x64, 0x8E, // 1
  0x1E, 0x21, 0x46, 0x68, 0x9F, // 2
  0x1E, 0x21, 0x4E, 0x61, 0x9E, // 3
  0x06, 0x2A, 0x5F, 0x62, 0x82, // 4
  0x1F, 0x30, 0x5E, 0x61, 0x9E, // 5
  0x06, 0x28, 0x5E, 0x71, 0x8E, // 6
  0x1F, 0x22, 0x44, 0x68, 0x88, // 7
  0x0E, 0x31, 0x4E, 0x71, 0x8E, // 8
  0x0E, 0x31, 0x4F, 0x62, 0x8C, // 9
  0x00, 0x24, 0x40, 0x64, 0x80, // :
  0x00, 0x24, 0x40, 0x6C, 0x80, // ;
  0x02, 0x24, 0x48, 0x64, 0x82, // <
  0x00, 0x3F, 0x40, 0x7F, 0x80, // =
  0x08, 0x24, 0x42, 0x64, 0x88, // >
  0x0E, 0x31, 0x42, 0x64, 0x84, // ?
  0x0E, 0x35, 0x57, 0x70, 0x8E, // @
  0x04, 0x2A, 0x5F, 0x71, 0x91, // A
  0x1E, 0x29, 0x4E, 0x69, 0x9E, // B
  0x0F, 0x30, 0x50, 0x70, 0x8F, // C
  0x1E, 0x29, 0x49, 0x69, 0x9E, // D
  0x1F, 0x30, 0x5E, 0x70, 0x9F, // E
  0x1F, 0x30, 0x5E, 0x70, 0x90, // F
  0x0F, 0x30, 0x53, 0x71, 0x8F, // G
  0x11, 0x31, 0x5F, 0x71, 0x91, // H
  0x0E, 0x24, 0x44, 0x64, 0x8E, // I
  0x01, 0x21, 0x41, 0x71, 0x8E, // J
  0x13, 0x34, 0x58, 0x74, 0x93, // K
  0x10, 0x30, 0x50, 0x70, 0x9F, // L
  0x11, 0x3B, 0x55, 0x71, 0x91, // M
  0x11, 0x39, 0x55, 0x73, 0x91, // N
  0x0E, 0x31, 0x51, 0x71, 0x8E, // O
  0x1E, 0x31, 0x5E, 0x70, 0x90, // P
  0x0C, 0x32, 0x56, 0x72, 0x8D, // Q
  0x1E, 0x31, 0x5E, 0x74, 0x92, // R
  0x0F, 0x30, 0x4E, 0x61, 0x9E, // S
  0x1F, 0x24, 0x44, 0x64, 0x84, // T
  0x11, 0x31, 0x51, 0x71, 0x8E, // U
  0x11, 0x31, 0x51, 0x6A, 0x84, // V
  0x11, 0x31, 0x55, 0x7B, 0x91, // W
  0x11, 0x2A, 0x44, 0x6A, 0x91, // X
  0x11, 0x2A, 0x44, 0x64, 0x84, // Y
  0x1F, 0x22, 0x44, 0x68, 0x9F, // Z
  0x07, 0x24, 0x44, 0x64, 0x87, // [
  0x10, 0x28, 0x44, 0x62, 0x81, // \
  0x1C, 0x24, 0x44, 0x64, 0x9C, // ]
  0x04, 0x2A, 0x51, 0x60, 0x80, // ^
  0x00, 0x20, 0x40, 0x60, 0x9F, // _
  0x0A, 0x2A, 0x40, 0x60, 0x80, // '
  0x00, 0x2E, 0x52, 0x72, 0x8D, // a
  0x10, 0x30, 0x5E, 0x71, 0x9E, // b
  0x00, 0x2F, 0x50, 0x70, 0x8F, // c
  0x01, 0x21, 0x4F, 0x71, 0x8F, // d
  0x00, 0x2E, 0x5F, 0x70, 0x8E, // e
  0x04, 0x2A, 0x48, 0x7C, 0x88, // f
  0x00, 0x2F, 0x50, 0x73, 0x8F, // g
  0x10, 0x30, 0x56, 0x79, 0x91, // h
  0x04, 0x20, 0x4C, 0x64, 0x8E, // i
  0x00, 0x26, 0x42, 0x72, 0x8C, // j
  0x10, 0x30, 0x56, 0x78, 0x96, // k
  0x0C, 0x24, 0x44, 0x64, 0x8E, // l
  0x00, 0x2A, 0x55, 0x71, 0x91, // m
  0x00, 0x36, 0x59, 0x71, 0x91, // n
  0x00, 0x2E, 0x51, 0x71, 0x8E, // o
  0x00, 0x3E, 0x51, 0x7E, 0x90, // p
  0x00, 0x2F, 0x51, 0x6F, 0x81, // q
  0x00, 0x33, 0x54, 0x78, 0x90, // r
  0x00, 0x23, 0x44, 0x62, 0x8C, // s
  0x08, 0x3C, 0x48, 0x6A, 0x84, // t
  0x00, 0x32, 0x52, 0x72, 0x8D, // u
  0x00, 0x31, 0x51, 0x6A, 0x84, // v
  0x00, 0x31, 0x55, 0x7B, 0x91, // w
  0x00, 0x32, 0x4C, 0x6C, 0x92, // x
  0x00, 0x31, 0x4A, 0x64, 0x98, // y
  0x00, 0x3E, 0x44, 0x68, 0x9E, // z
  0x06, 0x24, 0x48, 0x64, 0x86, // {
  0x04, 0x24, 0x44, 0x64, 0x84, // |
  0x0C, 0x24, 0x42, 0x64, 0x8C, // }
  0x00, 0x27, 0x5C, 0x60, 0x80, // ~
};

#endif  // _FONT5X5_H_

And finally, the changes in HDSP.ino are:

1. add the following line at the top:

#include "SCD5583.h"

// SCD5583 pins: LOAD to D4, DATA to D5, SDCLK to D3;
SCD5583 scd(4,5,3);

2. replace the function writeDisplay() written for HDSP-2534, with the following:

void writeDisplay()
{
  scd.writeLine(displayBuffer);
}

Hardware-wise, some re-wiring is required on the HDSP board, starting with the removal of the 595 shift register. Then, D3, D4 and D5 (ATmega328 pins 5, 6, 11) must be connected respectively to SDCLK, LOAD and DATA pins (1, 2, 27) of the SCD5583 display.

And there you have it, a working HDSP clock with SCD5583 display.

It is worth mentioning that the measured current drawn was between 10mA (lowest brightness) and 20mA (highest), and that it works similarly well when powered by 3V3.