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The LCD RGB KEYPAD for RPi and the Arduino

There are some I2C LCD shields available advertised for the Raspberry Pi. As these modules are using a MCP23017 they are equipped with 5 a RGB LED and 5 push buttons. Let's try to connect them to an Arduino or an ESP8266.

The LCD RGB KEPAD for RPi - Overview

The LCD RGB KEYPAD for RPi comes with following features:

  • A 16bit I2C port expander based on a MCP23017
  • 5 push buttons
  • a RGB LED
  • a 1602 LCD in with blue/white

LCD RGB KEYPAD for RPi

The I2C Expander MCP23017 for the LCD

As port expander a MCP23017 is used. The MCP23017 has 16 bits (channels), 7 channels are connected to the LCD in 4 bit mode, 3 channels are used for the RGB LED and 5 channels are inputs connected for the 5 buttons. One channel (GPA5) remains unused.

Pinmapping MCP23017 on LCD RGB KEYPAD for RPi

I name the push buttons like following:

buttons on the LCD RGB KEYPAD for RPi

Connecting Raspberry LCD Module to an Arduino or an ESP

The 26 pin header follows the pin layout of the Raspberry Pi. To connect the display to another microcontroller you can use Dupont wires on Pin 3 (SDA), Pin5(SCL), Pin 4 (5V) and Pin 6 (GND).

The pin layout from above (= like the RPi header):

pinout of LCD RGB KEYPAD for RPi

The Hardware Driver for the MCP23017

The LCD library offers a class for I2C displays connected with an MCP23017. It uses the 4bit mode. The RW pin is connected but unused.

The necessary #include and the constructor are:

#include <NoiascaLiquidCrystal.h>
#include <NoiascaHW/lcd_MCP23017.h>
LiquidCrystal_MCP23017_custompin lcd(addr, rs, rw, en, d4, d5, d6, d7, bl, POSITIVE, cols, rows);

Remember to add a Wire.begin() to your setup() like in the examples, as this will not be done in the library.

Noiasca Liquid Crystal and the Raspberry LCD Module

The "Noiasca Liquid Crystal" library does a character mapping from UTF-8 to the existing characters in the LCD ROM. As example some special characters in the second row of the display:

special characters LCD

(Degree, Division, middle Point, n with tilde, Pound, Yen, Tilde, Sqareroot, Proportional to, Infinity, Left Arrow, Right Arrow, Backslash)

You can read more about this character mapping in the Introduction or in the German section of this site. For the beginning you should just know that you don't need to enter the octal ROM addresses of the special characters manually and these print can be done by a simple:

lcd.print("°÷·ñ£¥~√∝∞←→\\");

The backlight of the cheap LCD RGB KEPAD for RPI is always on, you can't disable it.

The RGB LED

The LED on the "LCD RGB KEPAD for RPI" occupies 3 GPIOs of the MCP23017. To use a pin as output, you must setPinMode to OUTPUT.

lcd.setPinMode(rgbBlue, OUTPUT); // set the RGB pins to outputs

Now you can use the well known digitalWrite to switch the pin HIGH or LOW

lcd.digitalWrite(rgbBlue, LOW);

The LEDs are low active, switch to LOW to enable them, switch to HIGH to switch them off.

The Push Buttons

The 5 push buttons will connect a GPIO to GND. Therefore you should activate the built in pullups resistors of the MCP23017:

lcd.setPinMode(buttonPin, INPUT_PULLUP);

Now you can read the state of a button with a simple

buttonState = lcd.digitalRead(buttonPin);

Remember: By using the INPUT_PULLUP you will read a HIGH if the button is released and LOW if the button is pressed.

Additional methods for the MCP23017 displays

Before you use other pins of the MCP23017 set the pinMode to either OUTPUT, INPUT or INPUT_PULLUP

lcd.setPinMode(pin, OUTPUT);

To switch a pin use

lcd.digitalWrite(pin, HIGH);

To read a pin use

byte state = lcd.digitalRead(pin);

LCD Examples for the MCP23017

All LCD examples regarding displays with MCP23017 can be found in the folder 03_I2C_MCP23017.

Your own Character Converter

If you need a different character converter you can hand over a callback function as optional last parameter.

Obviously - you also have to implement the callback function to do all the magic.

See the examples in the folder "50_Convert" how to write your own character converter.

German Umlauts

For my German readers: the default constructor enables the support for the small letters ä ö ü and ß. The large German umlauts Ä Ö Ü (with diaeresis) will be converted to their counterpart A O U. If you want to try other variants, you can hand over different callback converter functions:

LiquidCrystal_MCP23017_custompin lcd(addr, rs, rw, en, d4, d5, d6, d7, bl, POSITIVE, cols, rows);                    // Ä becomes A
//LiquidCrystal_MCP23017_custompin lcd(addr, rs, rw, en, d4, d5, d6, d7, bl, POSITIVE, cols, rows, convert_ae);      // Ä becomes Ae
//LiquidCrystal_MCP23017_custompin lcd(addr, rs, rw, en, d4, d5, d6, d7, bl, POSITIVE, cols, rows, convert_small);   // Ä becomes ä
//LiquidCrystal_MCP23017_custompin lcd(addr, rs, rw, en, d4, d5, d6, d7, bl, POSITIVE, cols, rows, convert_special); // Ä becomes Ä

Summary

The MCP23017 class in "Noiasca Liquid Crystal" enables you to run LCDs with MCP23017 I2C port expander and adds more IOs for your usage.

Links

(*) Disclosure: Some of the links above are affiliate links, meaning, at no additional cost to you I will earn a (little) comission if you click through and make a purchase. I only recommend products I own myself and I'm convinced they are useful for other makers.

 

History

The MCP23017 is supported with library version 2.0 and higher.

First upload: 2021-06-03 | Version: 2021-06-04