See How Easy
Coding A Rotary
By Fred Eady
I can remember back when the only way to interface with a computer was
with a piece of hard paper called a punch card. Depending on the company
you kept, punch cards were also known as IBM cards or Hollerith cards. Time
passed and punch cards gave way to terminals. Again, depending on the
parties you attended, a terminal was an ASCII device or a 370 device.
Computing devices offered by DEC used VT-100 terminals while the IBM
mainframe crowd interfaced to their machines with clusters of 370 terminals.
In the beginning, terminals were monochrome devices and as time marched
on, the green and gray screens became colorful as DEC and IBM offered
newer and fancier color versions of the VT and 370 human interface devices.
PHOTO 1. This particular optical encoder mounts in a
standard 3/8 inch hole, has 32 detented positions, and an
SPST normally open at the bottom of its shaft.
Early computers aimed at the home and small business market also used various types of terminals as human input devices. In the late 1980s, IBM finally decided
that ASCII wasn’t a dirty word and produced the very
popular 3151 series of ASCII terminals. In fact, I have a
3151 in the closet and even today we still use a terminal of
sorts, which is part of today’s desktop PCs.
ASCII terminals found their way to embedded platforms
via the RS-232 protocol. Since ASCII terminals were not a
device that could be found in every household, PCs
equipped with terminal emulation software and RS-232
ports eventually annexed a huge amount of ASCII terminal
As embedded devices became smaller and more
portable, the ASCII terminal and PC terminal emulator no
longer fit the paradigm. Pushbuttons and LED displays
became the human interface components of choice for the
embedded designer. LEDs gave way to LCD devices and
discrete pushbuttons morphed into keypads. Today’s cell
phones are good examples of how far the LCD/keypad
combination has come.
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