![]() Examples: café (coffee), côte (coast), frère (brother), garçon (boy), ❾l niño? (The boy?). If Code and Shift are both asserted, the following 10 special characters can be typed: ^ ç é ` ¿ ~ §¶ (see Figure 2). This Code key is used to start and stop Bold, Center, Sub Script, Super Script, and Underline. To make things even more complicated, there’s a second type of Shift key called “Code.” If the Code key is held down and the letter b is struck, the following text will be Bolded. ![]() In the membrane keyboard, any low in gets a low out. In a wired-OR, any high in gets a high out. This is the opposite of what would be expected from a wired-OR circuit. I found by experimentation that ground takes precedence. Even stranger, this common output line is shorted to two inputs that could be in different states (one high, one low).Ĭan you predict what the output of such a circuit would be? Voltage half-way between high and low? Oscillation? Blown fuse? Undefined? Depending on the letter, it’s possible for both high lines to be the same line, so this one wire pulses low at two different times. If the Shift key is held down while a letter is struck, two high lines are involved: one for the Shift key and one for the letter. The high line follows whatever level the connected low line happens to be in, until the key is released when the high line returns to high. Next, the typewriter puts a high pulse 0.5 msec wide every 5 msec on every low line, but pulses are staggered so the typewriter can tell which low line is connected to the pressed key. With no key pressed, pin 3 and pins 12 through 18 are low (let’s call these the eight low lines), and pins 1, 2, and 4 through 9 are high (we’ll call these the eight high lines.) When any key is pressed, a high line is shorted to low. Pins 10 and 11 supply power to the Caps Lock LED. See text under “The Mystery of the Membrane Keyboard.” Given the state of Code and Shift, the secondary use is to generate the hexadecimal numbers (0 through F) which are used to populate the Flex Array. Primarily, this chart shows the relationships between the keyboard cable, the low lines, the high lines, and the Arduino Nano Every pins they connect to. The keyboard membrane cable has pins 1 to 18 (see Figure 1). I employed one of the three to indicate a non-printing character, such as BELL.) The Mystery of the Membrane Keyboard (There are 61 keys on the PWP keyboard, allowing for three unused combinations in the 64-slot matrix. Instead, it forms an 8 x 8 matrix which shorts two wires together when a key is pressed. The Smith-Corona keyboard does not output either serial or ASCII parallel codes. The Nano Every was chosen because it has a small form factor and a maximum power input of +21V, while the typewriter supplies +20V for its print head. I used an Arduino Nano Every to simulate the membrane keyboard, so that either an added RS-232 port or the existing keyboard could input text. In the absence of existing serial or parallel signals, the best way to input text to the typewriter was through its keyboard. I figured I would damage the chips this way, so I stopped scoping. In the process, I occasionally scoped a clock pin which halted the microprocessor. The first step was to use an oscilloscope to examine the typewriter chips, looking for traces that showed a serial signal or ASCII parallel signals. I decided on a method which did not use solenoids or actuators. Due to the bulk on the bottom, it wouldn’t fit on a tabletop. One hobbyist solved this problem by mounting a bank of car door lock actuators below the keyboard, using actuators tied to keys with strings. This prints correctly, but it prevents typing on the keyboard again until the solenoid bank is removed. Many experimenters have converted typewriters to printers by mounting a bank of solenoids on top of the keyboard. (In this age of wireless communication through the Internet of Things, the serial cable has been all but forgotten.) I also solved the mystery of the membrane keyboard and discovered some tips on creating with the Nano Every, which is surprisingly different from the original Arduino. Along the way, I re-discovered RS-232 serial cable transmission. I decided to emulate the membrane keyboard with an Arduino Nano Every, so that either an added serial port or the existing keyboard could input text. However, there was no way to use it as a printer. The daisy wheel print quality was perfect, and it included a self-contained word processor (PWP = Personal Word Processor). I bought a Smith-Corona PWP 78DS typewriter from Good Will for under $20. » Skip to the Extras With a Useable Keyboard, Courtesy of the Arduino Nano Every
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