Melcor 370: "First 100% Solid-State Calculator"

Melcor Electronics Corp., located in Farmingdale, New York was a significant but early manufacturer of small or pocket-sized calculators which didn't survive the decade of the 1970's.  It did however contribute some interesting calculators for collectors to ponder today and, it appears, did in fact make some history by offering to the trade the first fully solid-state calculators - its models 360 and 370, which were among the first models offered by the company in 1972-1973.

Here, we will consider the 370 as seen below.  Note that this calculator is missing its make/model label below the display but is otherwise not only intact but operable and, fortunately for us, also has its original instruction book.

At once the Melcor 370 can be seen to have an unusual feature; the model incorporates a touch pad instead of more normal keys or buttons.  This feature, referred to by Melcor as the Touch-Tronic keyboard, is described in the manual as follows:

"Your calculator features the Melcor space age Touch-Tronic keyboard which provides the ultimate in reliability.  With a little practice in the technique outlined below, you'll enter numbers and operations faster and more accurately:

1)  Entry is made by pressure on the key pad.  There is no actual movement.
2)  Approach the key pad with your finger nearly parallel to the top surface of the calculator.
3)  Bring the ball of your finger down rapidly into the key opening and apply moderate pressure to the key pad.
4)  Withdraw finger rapidly from the key pad.
5)  Do not attempt to brush or "tease" key.  The keyboard is very sensitive and this may result in entering two numbers.
6)  Do not use fingernails or other sharp objects on keyboard.  This may damage calculator and will void warranty."

In addition to not having an inbuilt debounce feature (which later calculators incorporate to prevent double or triple digit entry upon light pressure to a key) this calculator also shows another feature common to some very early calculators:  The Melcor 370 does not have automatic clear upon startup.  When the calculator is turned ON, the display will likely have a nonsensical number displayed with one, two, three or more decimal points.  The calculator must be cleared before any calculations can be done by depressing the C key.  Later calculators have an inbuilt automatic clear function upon startup.  Below, we see the Melcor 370 immediately after having been turned on; the gibberish result in the display (which is not repeating, but totally random) is proof that the calculator doesn't have clear-on-startup.  This feature of early calculators has carried on to modern users who instinctively clear calculators on startup even today, even though they've been built with clear-on-startup since the middle 1970's.

Once the calculator is cleared, another feature that a number of early calculators had but which was considered confusing and was later engineered out is shown; the calculator always powers all digits of the display, even if they are zeroes.  Eight digits are always displayed, and the decimal point floats to wherever it's required in the display.  Here is the calculator after having been cleared and awaiting the performance of actual work.

(Note that the right-most digit does in fact have a failed LED segment, upper right.) 

Performance of calculations with this machine can incorporate digits beyond the eight displayed as is described below in a shot from the Melcor 370 instructions; most calculators of this day would overload if beyond the display limit.

When a calculation is performed, as noted earlier and above, the display will still be fully lit all the way across; "automatic zero blanking" was still in the future.  Below is the result of muliplying 9 by 9 to get 81.

One feature the Melcor 370 does have is prevention of false entry on double key depression; this prevents two keys being pressed simultaneously from making an input on the second key to be hit.

Speaking of keys, it's the on/off key that really allowed Melcor to claim that this was the first 100% solid state calculator, since the use of the on/off key removes having any kind of mechanical power switch on the machine.

(Above - Melcor 370 instruction book front cover.)

And speaking of power - the Melcor 370 is, properly, a two-model range comprised of the sub-models 370B and 370R.  The 370B, which we're showing here, operated off of a disposable 9V battery but also had an AC adapter port.  On a number of early calculators of various makes and models, the use of the AC adapter would attempt to charge the disposable batteries, so the operator either had to ensure no battery was installed in AC operation or else in some cases a switch was supplied to ensure the battery didn't explode.  However, on the advanced Melcor 370 the battery was automatically disconnected when the calculator was AC powered.  The other variant, the 370R, included a non-replaceable, rechargeable nickel-cadmium battery pack which had to be recharged through use of the adapter.  According to the instructions, the 370R model would charge the battery whether the calculator was on or off, but would only charge at about 1/4 the normal rate if the calculator was being used while the battery was charging.  Interestingly, according to the book the 9V battery version would run about 7 hours in use before needing a new battery while the rechargeable version would only run about 4 hours before needing a recharge. 

As we know today, calculators with keypads didn't last long - either in use, or in a larger sense, on the market.  While several makers tried this kind of design in the early-mid 1970's it must have proven to be more trouble than it was worth, and all of them (including Melcor) changed to calculators using conventional keys (or "buttons").  Below, we see the Melcor 370 with the very next model, the 380 (which uses a very different keyboard and a new case) as well as the later 392 (same case as the 380 but with yet again different keys.)  We'll see more Melcor calculators on the blog so stay tuned.

Melcor 370, 380 and 392.  It's interesting to note that the oldest, the 370 at left, has the Touch-Tronic keypad and a single on/off key; the 380 at center has the Melcor Full-Travel keyboard with separate on and off keys, while the 392 at the right has a conventional on/off mechanical contact type switch.