Smoothieware does not have an option for driving character LCD. It can only drive graphical SPI LCDs. This is probably due to lack of GPIO pins (Ethernet functionality is using a lot of GPIO…)

Smoothieboard developer offers an add-on board, that can translate the SPI bitstream for I2C LCD and (The more common) parallel LCD.
This board has a complex shape and fits only on Smoothieboard, but The firmware is open source, called Universal Panel Adapter (UPA), is available in Github and can be used with Arduino boards or a plain ATmega328 microprocessor.

On this small project prj_UPA_minimal, we deploy UPA firmware on a minimal and tidy implementation, to be used with a 3D printer controller with SPI only GLCD interface like n-PRO-3DP, SmoothieBoard and other boards driven by Smoothieware.
With the UPA minimal Board, any 20x4 LCD can be used with Smoothieware.

The Board is developed in iterations: starting with a Breadboard 1st iteration, a perforated-board 2nd iteration and a PCB 3d iteration

Block Diagram

1st iteration: with Arduino-Nano on breadboard, to be replaced with the Minimal version

2nd iteration: Minimal Schematic

2nd iteration: Minimal Perforated-Board

3nd iteration: In progress...

To have a succesful compilation with Arduino IDE 1.8.11, for the Parallel LCD, I did the following:

• Included all dependencies in the project folder
• Changed some instances like #include <Encoder.h>, to #include "Encoder.h"
• Replaced all references to wiring.h with wiring_private.h

Links:

• http://smoothieware.org/panel
• https://stackoverflow.com/questions/42826755/wiring-h-missing-in-arduino/42827754
• https://github.com/nikoschalikias/firm-universal-panel-adapter

Below is the readme file from wolfmanjm firmware: universal-panel-adapter

Using a cheap Arduino mini pro, uno or nano this sketch allows you to interface a panel like Viki or a Parallel LCD with encoder via SPI.

Specifically used for running I2C and parallel panels on a Smoothie compatible board.

Prebuild bianries ready for upload to arduino are:-

• viki_panel_adapter.hex for viki/panelolu2
• parallel_panel_adapter.hex for parallel LCD

Default Wiring is as follows:-

SDA  -> A4
SCL  -> A5
ENCA -> D2
ENCB -> D3
Gnd  -> Gnd
+5v  -> +5v

 4 RS -> D9
 5 RW -> A0
 6 EN -> A1
11 D4 -> D5
12 D5 -> D6
13 D6 -> D7
14 D7 -> D8

 1 gnd
 2 +5v
 3 contrast
 15,16 backlight power (on some)
 
Encoder is connected to Nano
ENCA  -> D2
ENCB  -> D3
Click -> A2

MOSI -> D11 : 0.18
MISO -> D12 : 0.17
SCK  -> D13 : 0.15
SS   -> D10 : 0.16
BUSY -> D4  : 2.11 (or 1.30 on Azteeg X5) (And set panel.busy_pin in config to that pin)

add this to your config file on smoothie

panel.enable                                true              # enable panel
panel.lcd                                   universal_adapter #
panel.spi_channel                           0                 # spi channel to use (0- MISO 0.17, MOSI 0.18, SCK 0.15, SS 0.16)
panel.spi_cs_pin                            0.16              # spi chip select
panel.busy_pin                              2.11              # busy pin NOTE 1.30 on Azteeg X5

For compiling the following Arduino libraries are needed

• Encoder library from http://www.pjrc.com/teensy/td_libs_Encoder.html

For Viki and I2C based panels

• LiquidTWI2 from https://github.com/lincomatic/LiquidTWI2

For Parallel panels

• LiquidCrystalFast from https://www.pjrc.com/teensy/td_libs_LiquidCrystal.html