Arduino memory issue with old HP HDSP-2000 display chips

Question

I'm running into memory issues with an Arduino Nano driving some old HDSP-2000/HDSP-2011 chips.

I cannot seem to get the ASCII 5x7 array into PROGMEM and have it read properly. It's so low on memory that I set up a second Arduino to send char[] strings through I2C to keep the Nano from locking up. This sort of worked to my advantage that I can multi-task and I'll probably keep it that way but it still keeps locking up or spitting gibberish.

The display Arduino is constantly bit-banging the displays - multiplexed with two 14-bit (acts as one 28-bit) Serial in / parallel out shift registers and and 5 column drivers. All displays use 5 common anode + columns, which have to be pulse timed with the registers.

#include <Wire.h>


//*** HDSP2011 Display Demo
//*** ASCII-DEMO
//*** [email protected]
//*** Paul Huinink has a webpage on displays www.huinink.info and specifically HDSP200X series displays www.spagmon.com
//*** Modified December-2013 by Patrick Hickey: added HP HDSP single digit display and RGB LED
//*** Patrick Hickey [email protected]

//modified 3/2018 by Brandon McRee - removed support for LED and single digit HDSP DISPLAY



//figure out latch pin

// an array of 5 bytes per ASCII
// 5 bytes cause 5 columns
// 7 bits per column (no LSB)


const byte ascii_5x7[] = {    //when I put this in PROGMEM i get gibberish, without it the SRAM is 87% full... 
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0xF2, 0x00, 0x00,// !
    0x00, 0xE0, 0x00, 0xE0, 0x00,// "
    0x28, 0xFE, 0x28, 0xFE, 0x28,// #
    0x24, 0x54, 0xFE, 0x54, 0x48,// $
    0xC4, 0xC8, 0x10, 0x26, 0x46,// %
    0x6C, 0x92, 0xAA, 0x44, 0x0A,// &
    0x00, 0xA0, 0xC0, 0x00, 0x00,// 39
    0x00, 0x38, 0x44, 0x82, 0x00,// 40
    0x00, 0x82, 0x44, 0x38, 0x00,// 41
    0x28, 0x10, 0x7C, 0x10, 0x28,// *
    0x10, 0x10, 0x7C, 0x10, 0x10,
    0x00, 0x0A, 0x0C, 0x00, 0x00,
    0x10, 0x10, 0x10, 0x10, 0x10,
    0x00, 0x06, 0x06, 0x00, 0x00,
    0x04, 0x08, 0x10, 0x20, 0x40,
    0x7C, 0x8A, 0x92, 0xA2, 0x7C,//48 0
    0x00, 0x42, 0xFE, 0x02, 0x00,//49 1
    0x42, 0x86, 0x8A, 0x92, 0x62,//50 2
    0x84, 0x82, 0xA2, 0xD2, 0x8C,
    0x18, 0x28, 0x48, 0xFE, 0x08,
    0xE4, 0xA2, 0xA2, 0xA2, 0x9C,
    0x3C, 0x52, 0x92, 0x92, 0x0C,
    0x80, 0x8E, 0x90, 0xA0, 0xC0,
    0x6C, 0x92, 0x92, 0x92, 0x6C,
    0x60, 0x92, 0x92, 0x94, 0x78,
    0x00, 0x6C, 0x6C, 0x00, 0x00,
    0x00, 0x6A, 0x6C, 0x00, 0x00,
    0x10, 0x28, 0x44, 0x82, 0x00,
    0x28, 0x28, 0x28, 0x28, 0x28,
    0x00, 0x82, 0x44, 0x28, 0x10,
    0x40, 0x80, 0x8A, 0x90, 0x60,
    0x4C, 0x92, 0x9E, 0x82, 0x7C,
    0x7E, 0x88, 0x88, 0x88, 0x7E,//65 A
    0xFE, 0x92, 0x92, 0x92, 0x6C,
    0x7C, 0x82, 0x82, 0x82, 0x44,
    0xFE, 0x82, 0x82, 0x44, 0x38,
    0xFE, 0x92, 0x92, 0x92, 0x82,
    0xFE, 0x90, 0x90, 0x90, 0x80,// 70
    0x7C, 0x82, 0x92, 0x92, 0x5E,
    0xFE, 0x10, 0x10, 0x10, 0xFE,
    0x00, 0x82, 0xFE, 0x82, 0x00,
    0x04, 0x02, 0x82, 0xFC, 0x80,
    0xFE, 0x10, 0x28, 0x44, 0x82,
    0xFE, 0x02, 0x02, 0x02, 0x02,
    0xFE, 0x40, 0x30, 0x40, 0xFE,
    0xFE, 0x20, 0x10, 0x08, 0xFE,
    0x7C, 0x82, 0x82, 0x82, 0x7C,
    0xFE, 0x90, 0x90, 0x90, 0x60,// P
    0x7C, 0x82, 0x8A, 0x84, 0x7A,
    0xFE, 0x90, 0x98, 0x94, 0x62,
    0x62, 0x92, 0x92, 0x92, 0x8C,
    0x80, 0x80, 0xFE, 0x80, 0x80,
    0xFC, 0x02, 0x02, 0x02, 0xFC,
    0xF8, 0x04, 0x02, 0x04, 0xF8,
    0xFC, 0x02, 0x0C, 0x02, 0xFC,
    0xC6, 0x28, 0x10, 0x28, 0xC6,
    0xE0, 0x10, 0x0E, 0x10, 0xE0,
    0x86, 0x8A, 0x92, 0xA2, 0xC2,
    0x00, 0xFE, 0x82, 0x82, 0x00,
    0x40, 0x20, 0x10, 0x08, 0x04,
    0x00, 0x82, 0x82, 0xFE, 0x00,
    0x20, 0x40, 0x80, 0x40, 0x20,
    0x02, 0x02, 0x02, 0x02, 0x02,
    0x00, 0x80, 0x40, 0x20, 0x00,
    0x04, 0x2A, 0x2A, 0x2A, 0x1E,
    0xFE, 0x12, 0x12, 0x12, 0x0C,
    0x1C, 0x22, 0x22, 0x22, 0x22,
    0x0C, 0x12, 0x12, 0x12, 0xFE,// 100 d
    0x1C, 0x2A, 0x2A, 0x2A, 0x1A,// 101 e
    0x00, 0x10, 0x7E, 0x90, 0x40,
    0x12, 0x2A, 0x2A, 0x2A, 0x3C,
    0xFE, 0x10, 0x10, 0x10, 0x0E,
    0x00, 0x00, 0x5E, 0x00, 0x00,
    0x04, 0x02, 0x02, 0xBC, 0x00,
    0x00, 0xFE, 0x08, 0x14, 0x22,
    0x00, 0x82, 0xFE, 0x02, 0x00,
    0x3E, 0x20, 0x1C, 0x20, 0x3E,
    0x3E, 0x10, 0x20, 0x20, 0x1E,
    0x1C, 0x22, 0x22, 0x22, 0x1C,
    0x3E, 0x28, 0x28, 0x28, 0x10,
    0x10, 0x28, 0x28, 0x28, 0x3E,
    0x3E, 0x10, 0x20, 0x20, 0x10,
    0x12, 0x2A, 0x2A, 0x2A, 0x24,
    0x20, 0x20, 0xFC, 0x22, 0x24,
    0x3C, 0x02, 0x02, 0x02, 0x3C,
    0x38, 0x04, 0x02, 0x04, 0x38,
    0x3C, 0x02, 0x0C, 0x02, 0x3C,// x
    0x22, 0x14, 0x08, 0x14, 0x22,// y
    0x20, 0x12, 0x0C, 0x10, 0x20,// z
    0x22, 0x26, 0x2A, 0x32, 0x22,//123 {
    0x00, 0x10, 0x6C, 0x82, 0x82,//124 |
    0x00, 0x00, 0xEE, 0x00, 0x00,//125 }
    0x82, 0x82, 0x6C, 0x10, 0x00,
    0x20, 0x40, 0x40, 0x40, 0x80,
    0xA8, 0x68, 0x3E, 0x68, 0xA8,
    0xBE, 0x2A, 0x2A, 0x2A, 0xA2,
    0x00, 0x20, 0x50, 0xA0, 0x00,
    0x04, 0x22, 0x7C, 0xA0, 0x40,
    0x84, 0xFC, 0x04, 0x00, 0x20,
    0xFE, 0x02, 0x02, 0x12, 0x02,
    0x1C, 0x22, 0x14, 0x08, 0x36,
    0x4E, 0x3E, 0x60, 0x40, 0x40,
    0x0C, 0x12, 0x52, 0xB2, 0x1C,//136 ê
    0x08, 0x1C, 0x2A, 0x2A, 0x2A,
    0xF8, 0x40, 0x40, 0x3C, 0x02,
    0x7C, 0x92, 0x92, 0x7C, 0x00,
    0x42, 0x44, 0x38, 0x04, 0x02,
    0x20, 0x3E, 0x20, 0x3E, 0x22,
    0x10, 0x20, 0x3C, 0x22, 0x20,
    0x18, 0x24, 0x7E, 0x24, 0x18,
    0x1C, 0x22, 0x0C, 0x22, 0x1C,
    0x82, 0xC6, 0xAA, 0x92, 0x82,
    0x3A, 0x46, 0x40, 0x46, 0x3A,
    0x54, 0x54, 0x54, 0x54, 0x54,
    0x44, 0x28, 0x10, 0x28, 0x44,
    0x10, 0x10, 0x54, 0x10, 0x10,
    0x00, 0x70, 0x88, 0x88, 0x70,
    0x60, 0x90, 0x8A, 0x80, 0x40,
    0xFE, 0xFE, 0x92, 0x92, 0x92,
    0x0A, 0x1A, 0x2A, 0x4A, 0x8A,
    0x8A, 0x4A, 0x2A, 0x1A, 0x0A,
    0x28, 0x2C, 0x38, 0x68, 0x28,
    0x04, 0xFE, 0x80, 0x80, 0x80,
    0x4C, 0x92, 0x92, 0x7C, 0x00,//157 Ø
    0x04, 0x02, 0x7C, 0x80, 0x40,
    0x38, 0x44, 0x38, 0x44, 0x38,
    0xAA, 0x54, 0xAA, 0x54, 0xAA,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0xBE, 0x00, 0x00,
    0x38, 0x44, 0xFE, 0x44, 0x00,
    0x12, 0x7E, 0x92, 0x92, 0x42,
    0xBA, 0x44, 0x44, 0x44, 0xBA,
    0xA8, 0x68, 0x3E, 0x68, 0xA8,
    0x00, 0x00, 0xEE, 0x00, 0x00,
    0x50, 0xAA, 0xAA, 0xAA, 0x14,
    0x00, 0x80, 0x00, 0x80, 0x00,
    0x7C, 0xBA, 0xAA, 0xAA, 0x7C,
    0x12, 0xAA, 0xAA, 0xAA, 0x7A,
    0x10, 0x28, 0x54, 0xAA, 0x44,
    0x80, 0x80, 0x80, 0x80, 0xC0,
    0x00, 0x00, 0x00, 0x00, 0x00,
    0x7C, 0xAA, 0xBA, 0x82, 0x7C,
    0x80, 0x80, 0x80, 0x80, 0x80,
    0x00, 0xE0, 0xA0, 0xE0, 0x00,
    0x22, 0x22, 0xFA, 0x22, 0x22,
    0x00, 0x48, 0x98, 0xA8, 0x48,
    0x00, 0x00, 0xA8, 0xA8, 0x70,
    0x00, 0x00, 0x40, 0x80, 0x00,
    0x04, 0xF8, 0x10, 0x10, 0xE0,
    0x60, 0xFE, 0x80, 0xFE, 0x80,
    0x00, 0x00, 0x10, 0x10, 0x00,
    0x08, 0x00, 0x02, 0x04, 0x00,
    0x00, 0x48, 0xF8, 0x08, 0x00,
    0x00, 0xE8, 0xA8, 0xE8, 0x00,
    0x44, 0xAA, 0x54, 0x28, 0x10,
    0xF0, 0x04, 0x0C, 0x14, 0x2E,
    0xF0, 0x00, 0x12, 0x26, 0x1A,
    0xFE, 0xFE, 0xFE, 0xFE, 0xFE,
    0x0C, 0x12, 0xA2, 0x02, 0x04,
    0x1E, 0xA8, 0x68, 0x28, 0x1E,
    0x1E, 0x28, 0x68, 0xA8, 0x1E,
    0x1E, 0xA8, 0xA8, 0xA8, 0x1E,
    0x9E, 0xA8, 0xA8, 0xA8, 0x9E,
    0x9E, 0x28, 0x28, 0x28, 0x9E,
    0x1E, 0x68, 0xA8, 0x68, 0x1E,
    0x7E, 0x90, 0xFE, 0x92, 0x92,
    0x70, 0x8A, 0x8C, 0x88, 0x88,
    0x3E, 0xAA, 0x6A, 0x2A, 0x22,
    0x3E, 0x2A, 0x6A, 0xAA, 0x22,
    0x3E, 0xAA, 0xAA, 0xAA, 0x22,
    0xBE, 0x2A, 0x2A, 0x2A, 0xA2,
    0x00, 0xA2, 0x7E, 0x22, 0x00,
    0x00, 0x22, 0x7E, 0xA2, 0x00,
    0x00, 0xA2, 0xBE, 0xA2, 0x00,
    0x00, 0xA2, 0x3E, 0xA2, 0x00,
    0x10, 0xFE, 0x92, 0x82, 0x7C,
    0xBE, 0x90, 0x88, 0x84, 0xBE,
    0x1C, 0xA2, 0x62, 0x22, 0x1C,
    0x1C, 0x22, 0x62, 0xA2, 0x1C,
    0x1C, 0xA2, 0xA2, 0xA2, 0x1C,
    0x9C, 0xA2, 0xA2, 0xA2, 0x9C,
    0x9C, 0x22, 0x22, 0x22, 0x9C,
    0x44, 0x28, 0x10, 0x28, 0x44,
    0x3A, 0x4C, 0x54, 0x64, 0xB8,
    0x3C, 0x82, 0x42, 0x02, 0x3C,
    0x3C, 0x02, 0x42, 0x82, 0x3C,
    0x3C, 0x82, 0x82, 0x82, 0x3C,
    0xBC, 0x02, 0x02, 0x02, 0xBC,
    0x60, 0x10, 0x4E, 0x90, 0x60,
    0xFE, 0x44, 0x44, 0x44, 0x38,
    0x7E, 0xA4, 0xA4, 0x58, 0x00,
    0x04, 0xAA, 0x6A, 0x2A, 0x1E,
    0x04, 0x2A, 0x6A, 0xAA, 0x1E,
    0x04, 0xAA, 0xAA, 0xAA, 0x1E,
    0x84, 0xAA, 0xAA, 0xAA, 0x9E,
    0x04, 0xAA, 0x2A, 0xAA, 0x1E,
    0x04, 0x6A, 0xAA, 0x6A, 0x1E,
    0x2E, 0x2A, 0x1C, 0x2A, 0x3A,
    0x30, 0x4A, 0x4C, 0x48, 0x00,
    0x1C, 0xAA, 0x6A, 0x2A, 0x1A,
    0x1C, 0x2A, 0x6A, 0xAA, 0x1A,
    0x1C, 0xAA, 0xAA, 0xAA, 0x1A,
    0x1C, 0xAA, 0x2A, 0xAA, 0x1A,
    0x00, 0x80, 0x5E, 0x00, 0x00,
    0x00, 0x00, 0x5E, 0x80, 0x00,
    0x00, 0x40, 0x5E, 0x40, 0x00,
    0x00, 0x40, 0x1E, 0x40, 0x00,
    0x0C, 0x12, 0x52, 0xB2, 0x1C,
    0xBE, 0x90, 0xA0, 0xA0, 0x9E,
    0x0C, 0x92, 0x52, 0x12, 0x0C,
    0x0C, 0x12, 0x52, 0x92, 0x0C,
    0x0C, 0x52, 0x52, 0x52, 0x0C,
    0x4C, 0x52, 0x52, 0x52, 0x4C,
    0x0C, 0x52, 0x12, 0x52, 0x0C,
    0x10, 0x10, 0x10, 0x54, 0x10,
    0x18, 0x26, 0x3C, 0x64, 0x18,
    0x1C, 0x82, 0x42, 0x02, 0x1C,
    0x1C, 0x02, 0x42, 0x82, 0x1C,
    0x1C, 0x42, 0x42, 0x42, 0x1C,
    0x1C, 0x42, 0x02, 0x42, 0x1C,
    0x20, 0x12, 0x4C, 0x90, 0x20,
    0xFE, 0x48, 0x48, 0x30, 0x00,
    0x20, 0x92, 0x0C, 0x90, 0x20,


};



int column[] = {
    8,7,6,5,4}; // change this to other general input/output arduino-pins as you like d8=pin 1 
int data = 2;   // change this to other general input/output arduino-pins as you like
int clock = 3;  // change this to other general input/output arduino-pins as you like


int brightness = 2000; // keep high for max visibility. To high will cause flikkering 

const int numberOflDisplays = 4; // change this if total number of HDSP200x's is different.

int tekstDat[numberOflDisplays * 4 * 5]; // this is the array that store's what on the displays. 4 digits per display and 5 columns per digit.

unsigned long tijd; // used to trigger events in one of the examples below

char buf[40];
boolean flagRx = false; //allowed to receive if false



//*****************************************************************setup*************************************************************
void setup(){
    //Serial.begin(9600);

    for (int i = 0; i < 5; i++){
        pinMode(column[i], OUTPUT);
    }
    for (int i = 0; i < 5; i++){
        digitalWrite(column[i], LOW);
    }
    pinMode(data, OUTPUT);
    pinMode(clock, OUTPUT);
    digitalWrite(data, LOW); 
    digitalWrite(clock, HIGH);
    tijd = millis();


    Wire.begin(8);                // join i2c bus with address #8  >>important<<
    Wire.onReceive(receiveEvent); // register event

}

//***********************************************************************************end setup******************************************************

void loop(){


    char PROGMEM clr[] = "    ";
    char PROGMEM scroll[]  = "1979 TECH CONTROL PANEL by Brandon McRee";
    char PROGMEM scroll2[] = "Remember Stupid... you have to drive this home :)"; 


    if(flagRx == false){
        delay(10); //needs this delay to be stable
        scrollText(scroll, 8); //scrolling text, speed : second number is var howslow how slow this is a test of fastdraw text (short strings)
        delay(1000); 
        //scrollText(scroll2, 10);
        delay(10);          
        flagRx = true; // can now recieve    
    }
    else{
        writeText(buf);
        for (int i = 0; i< 50; i++) draw(); //does this continuously - display HDSP2011

    } 
    /*
            scrollText(scroll3, 10);
            delay(10);


        //short quick text write
        scrollText(hello, 8); 
        scrollText(world, 8);
        delay(500); 


            delay(5);
        writeText("TEST") ;                   //letters only? special charachters
        for (int i = 0; i< 100; i++) draw();
                delay(5);
        writeText("ABCDEFGHIJKLMNOPQRSTUVWXYZ") ; 
        for (int i = 0; i< 70; i++) draw();
                delay(5);
        writeText("1234567890") ;
        for (int i = 0; i< 100; i++) draw();
                delay(5);
        writeText("!@#$%^&*()") ;
        for (int i = 0; i< 50; i++) draw(); //delay??
                delay(5); 

        delay(1000);       


            */      


    writeText(buf);
    for (int i = 0; i< 50; i++) draw(); //does this continuously 












}
//****************end of main loop *********************************

void receiveEvent(int howMany) {

    int i;
    for (i=0; i<howMany; i++){      
        buf[i] = Wire.read(); //read I2C data (address 8)
    }

    flagRx = true;    // set flag, we received something. will figure out how to clear when

    // while (1 < Wire.available()) { // loop through all but the last     



}

//int x = Wire.read();    // receive byte as an integer not used
//Serial.println(x);          // print the integer






void writeDigit(int positie, int ascii){
    for (int i =0; i< 5;i++){
        tekstDat[(numberOflDisplays * 4 - positie) * 5 + i] = ascii_5x7[ascii*5+i];
    }
}

void scrollText(String tekkst, long howSlow){
    int leng = tekkst.length();
    for (int u=-numberOflDisplays*4;u<leng;u++){ // first N digits will be spaces. N = all digits of display. So one screen blank before first character apears.
        for (int v=0; v< numberOflDisplays*4;v++){
            if (( (u+v) >= 0 ) && ((u+v) < leng)){ // separete leading and tailing spaces from actual string
                char oneChar= tekkst.charAt(u+v);
                writeDigit(v+1, oneChar); // write the character of the string
            }
            else{
                writeDigit(v+1, 32); // write ascii-value 32 = a space.
            }
        }
        for (long teller = 0; teller < howSlow; teller++){
            draw();   
        }
    }
}

void writeText(String tekst){
    int tl = tekst.length();
    int spacesNeeded = 4 * numberOflDisplays - tl;
    if (spacesNeeded <0){
        tl = 4 * numberOflDisplays;    
    }
    else{
        for (int u = 0; u < spacesNeeded; u++){
            tekst.concat(" ");
        }
        tl = 4 * numberOflDisplays;    
    }
    char tekst_[tl];
    for (int vv = 0; vv < tl; vv++){
        char tt = tekst.charAt(tl-vv-1);
        for (int i =0; i< 5;i++){
            //tekstDat[vv*5+i] = ascii_5x7[tt*5+i]; //old using SRAM
            //tekstDat[vv*5+i] = (pgm_read_byte(ascii_5x7))[tt*5+i]; //new  try and read from PROGMEM does not compile :/
        }
    }
}

void dot(byte x, byte y, boolean oo){
    if ((x < (numberOflDisplays *4 * 5)) && (y < 7)){
        byte oldByte = tekstDat[x] & (0xFF - (2<<y));
        tekstDat[x] = oldByte | (2<<y);
    }
}

void draw(){
    for (int Kolom = 0; Kolom < 5; Kolom++){ // 5 columns to be strobed
        // pumping in 3 x 4 x 7 bits per one stobe of the column
        for (int displayNo = 0; displayNo < numberOflDisplays; displayNo++){  // number of  displays
            for (int digitNo = 0; digitNo < 4; digitNo++){ // 4 characters per display
                for (int diodeNo = 0; diodeNo < 7; diodeNo++){ // 7 row-elements
                    digitalWrite(clock, HIGH);
                    digitalWrite(data, tekstDat[Kolom + 5*(displayNo*4 + digitNo) ] &(2<<diodeNo)); // magic
                    digitalWrite(clock, LOW);
                }
            }
        }
        digitalWrite(column[Kolom], HIGH);
        delayMicroseconds(brightness);
        digitalWrite(column[Kolom], LOW);
    }
}

Answer 1

Take a look at an ASCII table such as the one here.

You could remove the first 32 ASCII characters which are the control characters and don't show up on the display. That would save 160 bytes. You will just need to make sure your index lines up.

You can then remove the last 127 characters which make up the extended character set. These are rarely used in the English language. This would save you an additional 635 bytes.

Overall that would save you 795 precious bytes.

Answer 2

Ran into the same issue. Added the following line to setup():

// The following line is magic needed for pgm_read_byte() to function.
if (millis() > 100000L) Serial.println((uint16_t) font, HEX);

Note the Serial.println() is never executed, but the compiler doesn't know that. Without this line pgm_read_byte() produces garbage. With this line added to setup() the code runs fine.

Disassembling the code it looks as if without the Serial.println((uint16_t) font) the compiler optimizes away the begin address of the array, dropping "font" from the symbol table.

Complete sketch at https://github.com/koendv/retroleds