Rapidman Model 1208LC Calculator
This calculator would normally not be a part of the museum because it has a liquid crystal display. But, this is a very early example of liquid crystal display technology being used for a calculator, and that made it worthy of inclusion in the museum. This machine was made in the middle part of 1973, at a time when Nixie Tubes were fading from the scene, Vacuum Fluorescent and Burroughs Panaplex-style displays were at their peak, and LED (Light Emitting Diode) displays were starting to take over. Liquid Crystal technology had been around for some time, but hadn't been leveraged as a method of display for calculators. Rockwell is credited as being the first company to use a liquid crystal display panel in a calculator, though Sharp in Japan was working on LCD displays for calculators at around the same time. Back in 1973 when this machine was made, the technology was new enough that there were concerns about the longevity of the displays, as well as manufacturing difficulties that made yields on the panels rather low. These factors combined to make the early LCD-based calculators not all that much less expensive then calculators using other display technologies. Combine that with the fact that the early LCD techology required a light source in order to be visible, the power-savings made possible by the LCD were offset by the power required to operate the light source for the panel. The success of these early LCD calculators was rather limited -- LCD technology needed to mature just a little bit more before it would take over. By the late part of the mid-1970's, the technology had strengthened to the point where liquid crystal displays began to displace other display technologies, and by the early 1980's had totally taken over as the preferred display means for most types of calculators.
Profile View of Rapidman 1208LC
This machine, while badged with the Rapid Data Systems & Equipment, Ltd. "Rapidman" trademark, wasn't really manufactured by this company. The guts of the machine were manufactured by Rockwell, offered as a complete assembly minus cabinet and power supply, to any vendor that wanted to license the technology. A number of other companies were OEM (Original Equipment Manufacturer) customers of Rockwell, including Sears & Roebuck (A large US-based department store chain), and Lloyds Electronics. Rockwell manufactured the integrated circuits and LCD display panel in their US-based high-technology facilities, and provided these parts to an assembly operation in Mexico that built the subassemblies that were sent to Rockwell's OEM customers. Rockwell's customers then provided a power supply and cabinet, assembled the electronics in the packaging, selling the finished calculator through their retail channels.
As an example, Sears & Roebuck offered a calculator identical in functionalilty (with some cabinetry and color-scheme differences) to the Rapidman 1208LC called the Model C1 under the catalog number of 801.58030. The C1 was sold in a number of color schemes, with off-white or light-blue case bodies with black keyboard bezels, and black and white keycaps.
Sears & Roebuck's Model C1
Photo Courtesy Don DiGalbo
A number of battery-powered variants were made by Rapid and Lloyds (and possibly Sears). On the bottom of the cabinet of the 1208LC is a sliding door that, when opened, reveals a fairly cavernous compartment that looks like it could fit at least four D-Cell batteries. The 1208LC in the museum has no electrical contacts in this compartment for batteries to connect to, but some other collectors have found variants which can be operated from battery power (albeit not for long because of he drain of the incandescent lamp used to light the display). In the case of AC-only machines, the compartment serves as a handy place for storing the power cord when the machine is not in use.
Incandescent lamp and plastic 'light pipe' for directing light to edge of LCD panel
The early liquid crystal panel used for the display on the 1208LC is quite different from the LCD displays used on calculators today. Early liquid crystal displays were of a type called "transmissive" LCD technology, where the liquid crystal material would transmit light from an independent light source toward the viewer when the liquid crystal material electrically stimulated. Today's liquid crystal devices operate on a principle called "reflective" technology, where ambient light is reflected back to the user's eyes depending on the state of electric charge on the liquid crystal material, which requires no additional lighting other than the ambient light in the area the display is being used in. The early transmissive LCD panel in the 1208LC uses a small incandescent light bulb that shines into a plastic 'light pipe' that spreads the light from the lamp out and directs it to the edge of the LCD panel. From there, light is blocked or not blocked by the liquid crystal material, resulting in either 'light' or 'dark' segments which form the display digits.
Detail of the LCD panel in operation
The digits on the display are made up using a seven-segment representation, with 'lit' segments having an incandescent white-yellow glow to them, on a dark background. The display panel has eight seven-segment digits, with each digit position having a right-hand decimal point. At the right end of the display, another position exists that contains a minus-sign for indication of negative numbers, and two circular features resembling a colon (:) which light to indicate an overflow/error condition. The early liquid crystal material used in these displays is very 'slow' compared to those used today, taking long enough to change state that the digits seem to almost morph into existence.
The Rapidman 1208LC's Main Circuit Board
The 1208LC is quite simple inside. A trio of large-scale integrated circuits made by Rockwell run the machine. It appears that two of the Large Scale Integrated Circuits (Rockwell 10417) are devoted entirely to driving the LCD display. The other LSI (Rockwell 15311) contains all of the calculating brains. The remainder of circuitry on the circuit board is a sprinkling of discrete components that provide power supply, clock generation and other peripheral function. The liquid crystal display module plugs into a special socket mounted directly to the main logic board. The socket provides the electrical connections to the LCD panel, as well as providing a physical structure to support the panel at the proper angle for lighting by the 'light pipe' assembly.
"Buss Bar" Keyboard Construction
The keyboard assembly consists of contact-type keyswitch modules arranged in a 4 X 5 matrix. Metal 'buss-bars' pressure-fit onto the terminals of the switches, providing an "X" and "Y" grid. Each of the buss bars are connected via an individual wire back to the main circuit board. The grid is scanned column at a time by the calculator IC, with the each row being monitored. When a key is pressed, the switch contact closes a connection between the key's row and column buss bars, and the 'coordinate' of the key in the grid is determined. From the coordinate of the key, the calculator logic can determine which key was pressed.
In terms of functionality, the 1208LC is a pretty basic machine. The calculator provides full floating decimal with leading zero suppression on the display. Numeric entry is right to left. The calculator performs the standard four functions, along with a percent function. Math is performed algebraicly, with the [=] key providing the result to a given problem. The [C] key clears entry on the first press, and clears the whole machine on the second successive press. An automatic constant feature works for multiplication and division. The [%] key simply multiplies the number in the display by .01 before completing any pending operation. For example, to calculate 10% of 25, the user would enter 25, [X], 10, [%], and the result, 2.5, is displayed. The machine locks the keyboard if an overflow or error condition occurs, requiring a single press of the [C] key to unlock, leaving the upper-most digits of the result on the display. Division by zero is properly trapped, resulting in an error indication.
Closer view of the IC's in the 1208LC
The machine operates quickly, with all operations taking just over a blink of an eye to complete. The display is blanked while calculations are in progress, so the user notes a slight flicker during calculation. As mentioned before, the early liquid crystal material used in the display is quite slow, and the display actually takes a fraction of a second to settle in to the final result.