The IMPERIAL, model SPECIAL, is a 70s pocket calculator manufactured in Japan. It is a basic calculator measuring 118 mm × 72 mm × 25 mm with square root and percentage functions. It uses the LI2006 single chip calculator solution by the Sharp Corporation, which does all the work from decoding the keyboard to driving the fluorescent display.
The display is extremely bright as it uses VFD technology. Fluorescent displays are always much brighter than LCD and LED, and consequently this is a desirable item even today.
This calculator operates on a pair of AA sized batteries; however, the fluorescent display requires much more than 3 V to operate. Consequently, there is a dc-dc power supply circuit to provide the required voltage rails.
It has a membrane keyboard, and the keys are hard plastic. It is a simple and clean design that works well.
One of the best things about this calculator is that you can charge the batteries whilst they are still in the calculator. For this function to work, the switch must be in the charge position.
This is an external power socket for connecting a mains adapter, which allows you to use the calculator and charge the batteries.
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Imperial Special Calculator
Inside Imperial Special Calculator
Imperial Special PCB Design
Sharp LI2006 Voltage Levels
Imperial Special Calculator Display
Imperial Special Calculator Battery
Imperial Special Calculator Case