John Calhoun’s Adam74 Is a Teensy-Powered Textual content-Based mostly Terminal for the Fashionable Age



Engineer and retro-computing fanatic John Calhoun has put collectively a contemporary tackle the text-based terminal, impressed by the Lear Siegler ADM-3A and the Apple I “ASCII bus”: the Adam74.

“One thing that struck me studying concerning the historical past of the Apple I laptop was the pretty easy ‘ASCII bus’ that it used for enter and output,” Calhoun explains. “As I perceive it a hobbyist again within the day may get an ASCII keyboard that fairly actually introduced as an interface a header giving 7-bits of ASCII and an extra strobe pin that indicated {that a} key had been pressed. Briefly, ASCII is available in from a keyboard, ASCII goes out to the TV buffer.”

Calhoun fancied recreating one thing comparable utilizing fairly extra elements, with a view to constructing the show portion of a text-based terminal just like the Lear Siegler ADM-3A — naming it the Adam74 in homage to the system and the period by which it might have been used. “The Adam74 is a bit of venture that tries to behave because the latter half of the above ‘ASCII bus,'” Calhoun explains. “It’s briefly a bit of terminal {that a} hobbyist may take pleasure in utilizing for a small eight-bit laptop they’re experimenting with.”

Constructed round a Teensy 4.0 microcontroller board linked to an ILI9341-based 320×240 LCD panel and level-shifter, the Adam74 acts as a 40-column 24-line show — however accepts ASCII textual content, fairly than bitmap graphics, mechanically dealing with points like buffering, cursor dealing with, scrolling, and line-wrap. There’s even a buzzer, able to responding to a terminal bell management code — identical to a conventional terminal would.

“Initially my Adam74 had a small LED to point the facility was on however I in the end eliminated it as a result of I really feel there are simply too many LEDs on gadgets that point out the facility is on. Moreover, you hear the beep sound when the Adam74 boots up and you must have a blinking cursor immediate after,” Calhoun provides.

“In order that you may interface the Adam74 throughout a wider voltage vary, I added a level-shifter chip. Additionally, as soon as I by chance swapped the facility and floor wires and let loose the magic smoke from the LCD panel. After that mishap I added a small diode to hopefully shield the show ought to it occur once more.”

Extra particulars on the venture can be found on Calhoun’s web site, Engineers Want Artwork, whereas the supply code, PCB manufacturing information, and a template for an non-compulsory laser-cut acrylic stand have been printed to GitHub below an unspecified open license.

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