Links

• 00:00 EFTPOS
• 08:43 i2c_port_address_scanner.ino
• 09:21 https://github.com/tronixlabsAU/LCDbackpack
• 10:17 https://www.instructables.com/id/I2C-LCD-on-NodeMCU-V2-With-Arduino-IDE/
• 11:20 https://github.com/fdebrabander/Arduino-LiquidCrystal-I2C-library
• 19:40 ICS Expander MCP25S17
• 21:00 https://github.com/n0mjs710/MCP23S17
  https://github.com/adlerweb/MCP23S17

Quellcode Testsoftware

#include <Arduino.h>
#include <SPI.h>
#include <MCP23S17.h>
#include <Wire.h>
#include <LiquidCrystal_PCF8574.h>

extern "C" {
    #include "user_interface.h"
}

const char* kbdmap = "K##.0CRE321MSO654FTe987U";
const char* cmdmap = " +-*/";

#define ROWS 4
#define COLS 6

LiquidCrystal_PCF8574 lcd(0x27);
MCP gpio(0, 15);
int8_t last = 0;

String num1, num2;
byte cmd = 0;

void setPinMode(void) {
    uint16_t out = 0xFFFF;
    out <<= (ROWS);
    gpio.pinMode(out);
    gpio.pullupMode(out);
    gpio.inputInvert(out);
    out = ~out;
    gpio.digitalWrite(out);
}

void startLCD(void) {
    int error;
    Serial.println("LCD...");
    Wire.begin(D1, D2);
    Wire.beginTransmission(0x27);
    error = Wire.endTransmission();
    Serial.print("Return: ");
    Serial.print(error);

    if (error == 0) {
        Serial.println(": LCD found.");
    } else {
        Serial.println(": LCD not found.");
    }

    lcd.begin(20, 2); // initialize the lcd
    lcd.home();
    lcd.clear();
    lcd.print("BitBa // POS-Matrix");
}

void setup() {
    Serial.begin(115200);
    Serial.print("\nInit...");
    gpio.begin();

    setPinMode();

    Serial.println("OK");

    startLCD();
}

int8_t checkKeys(void) {
    byte row, col;
    int input;
    for(row = 0; row < ROWS; row++) {
        gpio.digitalWrite(row, LOW);
        delay(1);
        input = gpio.digitalRead();
        gpio.digitalWrite(row, HIGH);
        for(col=0; col < COLS; col++) {
            if(input & (1<<(ROWS + col))) {
                return (byte)(COLS * row + col);
            }
        }
    }
    return -1;
}

void loop() {
    int8_t input = checkKeys(); 
    int8_t check = 0xFF;
    float result = num2.toFloat();
    bool change = false;
    if(result == 0) result = num1.toFloat();

    if(input < (COLS*ROWS) && input >= 0 && last != input) {
        Serial.print(input);
        Serial.print(": ");
        last = input;
        if(input >= 0) {
            check = kbdmap[input];
            Serial.print(check);
        }else{
            check = 0xFF;
        }
        Serial.println();
        delay(15); //Poor maker debounce
    }else{
        check = 0xFF;
    }

    if(check != 0xFF) {
        switch(check) {
            //K##.0CRE321MSO654FTe987U
            case 'K':
                cmd = 4;
                change = true;
                break;
            case 'R':
                cmd = 3;
                change = true;
                break;
            case 'S':
                cmd = 2;
                change = true;
                break;
            case 'T':
                cmd = 1;
                change = true;
                break;
            case 'C':
                cmd = 0;
                num1 = "";
                num2 = "";
                change = true;
                break;
            case 'U':
                cmd = 0;
                num2 = "";
                change = true;
                break;
            case 'F':
                if(cmd == 0) {
                    if(num1.length() > 0) num1.remove(num1.length()-1);
                }else{
                    if(num2.length() > 0) num2.remove(num2.length()-1);
                }
                change = true;
                break;
            case '#':
                switch(cmd) {
                    case 1:
                        result = num1.toFloat() + num2.toFloat();
                        break;
                    case 2:
                        result = num1.toFloat() - num2.toFloat();
                        break;
                    case 3:
                        result = num1.toFloat() * num2.toFloat();
                        break;
                    case 4:
                        result = num1.toFloat() / num2.toFloat();
                        break;
                }
                cmd = 0;
                num1 = result;
                num2 = "";
                change = true;
                break;
            case '.':
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                if(cmd == 0) {
                    num1 += (char)check;
                }else{
                    num2 += (char)check;
                }
                change = true;
        }

        if(change) {
            lcd.clear();
            lcd.setCursor(0, 0);
            lcd.print(num1);
            if(cmd > 0) {
                lcd.setCursor(18, 0);
                lcd.print(" ");
                lcd.print(cmdmap[cmd]);
                lcd.setCursor(0, 1);
                lcd.print(num2);
            }
        }
    }
}

Hinweis: Der bei 19:40 gezeigter GPIO-Expander wurde mir seinerzeit von ICStation.com zur Verfügung gestellt.