arduino-lcd-writer

Driver code for arduino that enables writing to LCD from Linux

Goal

Serial devices get assigned (at least on my machine) to /dev/ttyACM* (e.g. ACM0). My goal is to be able to write to /dev/ttyACM0 and get the text displayed on the LCD display. For example, a command like echo "Hello, world!" > /dev/ttyACM0 would result in "Hello, world!" being printed on the LCD.

To this end, I wrote this program. It simply reads the serial port and prints the string to the screen, with one big idiosyncracy: since \n isn't handled by the lcd.print() function, I make ? denote a newline. Hence, if the arduino reads something like Hello?World on the serial bus, it will print "Hello" on the first line and "World" on the second.

Dependencies

This project depends on Arduino and Arduino-Makefile. Unfortunately, my distro doesn't supply Arduino Makefile so I have to have the operation dependent on a bunch of environment variables. Many distros don't supply the Arduino libraries outside of the IDE so you probably have to install that.

Arduino configuration

I follow the exact wiring of the official LCD tutorial. I have the 16 pin, 16x2 LCD screen used in that tutorial. If you have a different size, you can adjust the code.

Building

Download Arduino-Makefile and put it somewhere. Don't bother building or installing it unless you want to. Simply clone this repository, open Makefile, and set the ARDUINO_DIR, ARDMK_DIR, and AVR_TOOLS_DIR to appropriate values. ARDMK_DIR should be wherever you downloaded Arduino-Makefile. e.g. on my setup, the three variables are set to /usr/lib/arduino, ~/.local/Arduino-Makefile, and /, respectively. Then,

Build the program with make

Upload the program with make upload

Notes

Here I compile some notes on operation that would be a pain to search otherwise

How to run the program 100% successfully

By default, uploading this program and then writing to the serial device doesn't work for some reason. I follow these steps in this order to ensure correct operation. This assumes the program has already been uploaded to the Arduino.

1. Run make reset in the program directory - this resets the serial interface
2. Run tail -f /dev/ttyACM0 > /dev/null - this creates a process that constantly listens on the serial connection, keeping it alive? I'm not sure but it doesn't work without this.
3. Write stuff to the serial device - now it should work

Previously was working

I basically had to rewrite this from scratch - the Arduino had the program uploaded on it but I lost the code. That version had fast refresh rates but this one takes like 2 seconds to refresh the LCD. I don't have any applications that would break due to this so it isn't important. I fixed this issue. Apparently Serial.readString() is extremely slow, but Serial.readStringUntil('\n') (equivalent in this case) is much faster. Not sure on why but it works. I have effectively instant updates now.