|Sharp EL-811, EL-816, and EL-8102.
The first battery-powered portable calculator, the Sharp EL-8, was introduced in 1970, and was followed by the EL-8M in 1971. The three battery-powered portables described here followed in 1972 and 1973.
All three calculators are built in a wedge-shaped plastic casing that measures 105mm wide, 175mm deep, and 45mm high. The casing has brushed metal trim panels on the top and sides, and a carrying strap on the left-hand side. The calculators are slightly wider and longer than the EL-8, but only about half the height. They each weigh about 560g, including their rechargeable NiCad batteries.
Although almost identical on the outside, these three machines have significant internal differences. They provide a good example of the progress that was made in construction techniques, circuitry, and operator interfaces in the early 1970s.
To put these machines in their historical perspective, readers should review the description of the EL-8 and EL-8M before proceeding.
EL-811 external view
The EL-811 is a basic four-function eight-digit calculator with a single memory register. The dual-function Multiply-and-Divide key from the EL-8 has been replaced with two separate keys. The double-precision multiplication mode from the EL-8M has been retained, but this is now separate from the Memory function and has a separate double-arrow key to recall the extended product. The calculator has an automatic Constant function with a visual indication, with an unusual method of clearing the constant via the Minus key.
EL-811 internal view
The EL-811 is constructed in a similar manner to the EL-8 and 8M, but in a more compact arrangement. The keyboard is a one-piece plastic module using glass reed switches, similar to the EL-8. The light metal frame attached to the keyboard supports an edge connector and card guides for the processor board. A small board carrying the display tubes is attached to the main board via a pair of connectors arranged vertically near the centre of the machine. The clip-on battery pack is at the rear, with the display tubes and the inverter module underneath. The battery and charger are the same as in the EL-8.
EL-811 internal view without battery
This view with the battery removed shows the SanKen inverter module at the rear of the machine. The plastic frame around the inverter is fastened directly to the casing, rather than to the keyboard and display as previously. The inverter is connected to the processor board through five leads and a low-profile polarised plug and socket.
EL-811 CPU board
The single-sided phenolic circuit board has a component area of 86 x 73mm. The processor uses two Rockwell chips, numbered 10580 and 10631, with date codes in June of 1972. There are three NEC μPD193C display driver chips, one Hitachi HD9005, and three discrete transistors.
EL-811 display board
The eight-segment "script" numerals from the EL-8 (Itron DG10L tubes) have been replaced with the now-familiar seven-segment "slanted rectangle" numerals.
The Futaba DG10Q1 tubes are 10mm in diameter and 27mm tall, with numerals 8mm high. A special SP10D6 indicator tube at the right has symbols "I" for memory, "K" for Constant, "-" for Minus, and a double-arrow for double-precision calculations. The tubes are mounted on short un-insulated legs on a small double-sided board (95 x 30mm) which plugs in to the processor board. A plastic and rubber bracket supports the tubes and keeps them in alignment.
EL-816 external view
The EL-816 is functionally the same as the EL-811, except that it provides manual control of the Constant function via a separate "K" key. This simple change required the entire keyboard to be moved forward to make room for an additional row of keys at the top. At the same time, the previous moulded reed-switch assembly was replaced with individual key switches soldered directly to a printed wiring board, to provide greater flexibility in the keyboard layout. The key tops and general appearance remain identical to the EL-811.
EL-816 internal view
While the overall layout remains the same, this internal view shows substantial simplifications and cost reductions compared to the previous models.
The EL-84 battery pack remains at the rear of the machine, with the display tubes and inverter module underneath. The separate display board and its connectors have been eliminated, with the tubes now soldered directly to the main circuit board. Although the main board still has contact fingers for an edge connector, the connector has been deleted and the fingers are hard-wired directly to the keyboard PCB.
EL-816 CPU board
The EL-816 circuitry is built on a single-sided board that measures 90 x 95mm overall. The board carries a single Rockwell 15340 processor chip and two Toshiba TM4356 display drivers. The main chip has a date code 7335 (August 1973), and the drivers 3.F (June 1973).
The display uses eight ISE DG10F1 tubes, with the special indicator tube at the right-hand side. The plastic and rubber bracket which supports and aligns the tubes has been removed for illustration.
The DG10F1 tubes show rectangular numerals similar to those of the EL-811. The tubes actually contain an eighth segment at the right-hand side to provide a proper crossed 4, but this segment is not used in the EL-816.
The cost savings from eliminating the separate display board and connectors will have been partially offset by re-introducing the labour cost for insulating and hand-assembling the tube leads.
EL-8102 external view
The EL-8102 is externally similar to the EL-816, but with the +/= and -/= keys replaced by separate keys for plus, minus, and equals. The K key has been deleted and the automatic constant reinstated, operating in the now-familiar manner. The double-precision mode and the display-shift key have also been deleted. The deleted keys have been replaced with new square root and percentage functions.
(Note that the lower part of the display is obscured in this view. All three calculators have been photographed from exactly the same position, but the different internal arrangements of the display tubes requires a more upright viewing angle).
EL-8102 internal view
The internal construction of the EL-8102 is similar to the EL-811. The battery is still located in the same place above the inverter, but it is now in a compartment moulded into the outside of the case rather than being on the inside.
EL-8102 CPU board
The EL-8102 board is similar to the EL-816. It carries a single NEC μPD277C processor instead of the previous Rockwell chips. There is also one Toshiba TM4358 display driver chip dated September 1973, and 4 discrete transistors.
The display uses the same DG10F1 tubes as the EL-816, but still only drives 7 of the 8 segments. The special indicator tube has been replaced with another DG10F1 which shows a rectangular "C" for Error, - for minus, and the decimal point for the memory indicator.
The inverter module
All three of the calculators have a DC-to-DC inverter module mounted at the rear of the casing. The modules are similar but not identical, and are not interchangeable.
The complex AC/OFF/DC switching in the EL-8 has been replaced with a simple ON/OFF switch, and an automatic change-over switch in the charger input socket.
The EL-811 module (illustrated) has a low-profile 5-pin output connector. The EL-816 needs six wires, but uses the same connector plus an additional lead with a single pin-and-socket connection. The EL-8102 needs seven wires, but still uses the 5-way connector and two additional single-pin connections.
Batteries and chargers.
The EL-811 and EL-816 use the same EL-84 internal battery pack and EL-81 external charger as the EL-8. Please see the EL-8 page for full details.
EL-8102 battery packs.
The EL-8102 has an externally-accessible battery pack which clips into the rear section of the case from underneath. The standard pack (front right) holds six disposable AA cells, while the optional EL-95 pack (top right) holds six rechargeable NiCads.
The EL-95 NiCad pack uses the same EL-81 charger as the previous models. When fitted with the disposable battery pack, the calculator can be used with an AC adapter model EA-13A, which supplies a nominal 9V DC through the same input connector. The different contact arrangements on the battery packs guard against incorrect usage.
EL-811 operator's view
The three calculators show the development of the user interface from the rather cumbersome operation of the EL-8M to the now-conventional EL-8102.
All three have just a simple ON/OFF power switch and an automatic power-on reset. The EL-811 (illustrated) has replaced the earlier combined Multiply-and-Divide key with two separate keys. It retains the "double-precision" multiplication mode of the EL-8M, but this is now separate from the memory functions and does not require operation of the M/D (Memory/Double) switch. A double-arrow key switches between the upper and lower portions of the result, with a corresponding indicator in the display to show when the lower portion is active.
The Memory function uses only two keys: M+ and a combined MR/MC. Values can be subtracted from the memory by using the Change Sign key first. The EL-811 engages an automatic Constant function whenever Multiply or Divide is pressed, and lights a K indicator in the display. The constant can be cleared by pressing the red Minus/Equals key. A small red and green label on the front panel explains this unusual function.
Operation of the EL-816 is basically the same, except that the Constant function and indicator are now engaged manually via the additional "K" key.
The change to the NEC processor in the EL-8102 introduced a slightly different method of operation with separate keys for plus, minus, and equals. The new chip finally provided an automatic constant function that worked in the now-familar manner, and allowed the deletion of the K key and the indicator. The double-precision mode and the display-shift key were also deleted, but the memory operation was unchanged. The deleted keys were replaced with new keys for square roots and percentages, finally expanding the calculating capacity beyond the basic four functions.