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shiTTY

a while back, i pulled a 40*2 character lcd text display out of a gps time server. i had a play around with it, but couldn't figure out how to talk to it from an arduino. so i left it sitting on my desk for a while.

a few days ago, i found out that a library exists for the chip inside it (an HD44780, for those interested). what followed was probably one my best worst idea yet.

i decided to turn this thing into a terminal. it displays text, right? this totally isn't a stupid idea.

so i wrote some c, and here we are. i have a two line terminal. it's awful and i love it.

shiTTY v1 has scrolling, hardware clearing, a contrast adjuster (with 10x the resistance it needs) and an led. it takes data over usb at 9600 baud and displays it.

it also has a *backslash translation unit*. the character set of the display is regular 7 bit ascii, with a japanese upper codepage. HOWEVER. instead of regular 0x5c ascii backslash, it has a yen sign. this is not ideal.

luckily, the chip has some CGRAM, or character generator ram. this allows you to create 10 arbitrary characters while the display is turned on. shiTTY makes a backslash and tells the display to display that when it gets 0x01 (not 0x00 because that would fuck up c string handling). it then translates any incoming backslashes to 0x01 before sending them to the display and storing them in the internal buffer.

in conclusion: do stupid things. it's fun.

the code definitely works on arduino IDE 1.8.19, targeting a duemilanova. no guarantees for other boards or IDE versions. the specific display i'm using is a WH4002A-TMI-JT#, but it should work with any 2-line HD44780 display if you change the #define WIDTH 40. again, no guarantees, i can't test it on anything other than my own hardware.

v1 source code (only one file!)

demo image

https://ambylastname.xyz/projects/shiTTY

wiring diagrams soon tm

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