Wednesday, February 6, 2013

After the HP-41C

HP28C Opened
The HP-41C series remained as Hewlett Packard's top calculator for 8 years. In 1987, HP took a new direction and introduced the HP-28C, a graphing calculator with a new operating language called RPL. It featured the ability to enter and solve equations symbolically. The packaging also made a radical departure from the traditional slab style by replacing it with the so-called "clam shell" case. The left side of the case had an alphanumeric keyboard while the right side had the traditional scientific keyboard. The display was an LCD matrix which allowed to display either 4 lines of data or a graph.

The RPL programming language was not as intuitive as the former RPN. It came with two user's guides, totaling about 675 pages demonstrating the complexity of the calculator. This and the lack of ability to import or export programs limited the popularity of the model for programming development and sharing. On the other hand, its extensive built-in library of math, statistical, conversion and financial functions made it extremely powerful.
HP-28C Closed

Infrared Printer
Shown here (above and right) is a 28C that I found on eBay. Since the 28C was very quickly superseded by the HP-28S in 1988 having 4x the memory, the 28C does not fetch a very high price. This one was fully working with a good battery compartment (a common problem) and in otherwise good condition except for a blemish on the front cover.

The HP-28C had the ability to wirelessly connect to a printer via an infrared transmitter. Shown here (left) is one I found on eBay for not much. This model printer is still sold today to connect to HPs current graphing calculators.

HP enthusiasts were not happy with the move away from the intuitive RPN to RPL. To answer their concern, HP introduced in 1988 the HP-42s. This calculator was compatible with the HP-41C series but offered a more compact package and utilized a unique menu system which allowed to reduce the number of keys and the number of functions assigned to one key. While it had all the functionality of the earlier HP-41C, it lacked connectivity. It could not import or export programs and it could not connect with peripherals.

Free42 - an HP-42s Emulator for the iPad
With these two calculators, the HP-42s and the HP-28S, HP would start on a dual product line.  The former would be the traditional non-graphing RPN calculator with sequential programming. The later, a line of graphing calculators based on RPL. The HP-28S remained in production until 1992 when it was replaced by a more advanced graphing calculator without the clam-shell design, the HP-48 series. The HP-42s continued to 1995 with no real replacement. Other lower function RPN scientific calculators would follow, but the HP-42s remains among the most coveted calculators by HP enthusiasts. Prices on eBay start around $150 and go as high as $400 for boxed examples. For this reason, I don't have one of these (yet). I do however have an emulator app called Free42 that runs on my iPhone and iPad. It does everything that the original does, but for free!

Saturday, February 2, 2013

The HP-41C

Hewlett Packard took a while to come back with an answer to the Texas Instruments TI-59. They knew that a revolution rather than an evolution was needed. Their response came in 1979 with the HP-41C. This handheld calculator featured an alphanumeric display and continuous memory. No longer was it necessary to have a magnetic card reader to save programs. The alphanumeric display made it possible to prompt for input and to display results with meaningful labels. It also made programming easier as the instruction mnemonics could be displayed rather than key positions. Also, rather than having multiple shift keys and multiple functions per key, functions could be selected by spelling out their mnemonics.  The calculator proved to be very popular and was sold by HP all through the 1980's

I never had one of these back in the day. I considered buying one in college, but I was unable to sell my SR-52 and couldn't afford the $295 price tag. The one shown here is an HP-41CV which was an upgraded model introduced in 1980. I found it on eBay in 2012. It had some broken screw wells and some corroded contacts which prevented all the expansion slots from working. It has been repaired and is now fully functional.
A key feature of the calculator was that it was more than just a standalone unit, it was a platform for expansion. It featured four ports on the top of the unit which would accept ROM pacs and other accessories. ROM pacs could be purchased that contained programs targeted for specific markets like business, math, physics, surveying, etc. Other pacs expanded the programability features of the calculator or added memory capacity.

Shown here are 3 ROM pacs installed. The X Functions pac adds more functions to the calculator. The X Memory adds memory and the Math pac adds Math programs.

Another expansion feature of the unit was an I/O port on the side which allowed more advanced peripherals like plotters, data acquisition equipment, etc to be connected. This made the calculator popular among many specialized engineering and scientific disciplines.

Even though a card reader was no longer necessary, one was available as an option to allow to free up memory for new programs while saving older programs for later use. The card reader unit attached to the top of the calculator using one of the expansion ports. The magnetic cards used were the same as those used by the HP-67 and in fact the unit had the capability to convert the HP-67 programs to HP-41C programs.

When attached it made the calculator somewhat long and unwieldy, but it could easily be removed when not in use.

The reader shown here was found on eBay, not working. The same design for the reader mechanism was used as the HP-67 so it suffered from the same "gummy wheel" problem whereby the rubber wheel driving the cards through the reader would turn to sticky gum. This one also had a bad transistor which I replaced. It is now fully working.
For the HP-41C series, HP decided to have an attachable printer. Luckily they made the unit much more compact and attractive than TI's PC-100A. It easily attaches into one of the 4 expansion ports on the top of the calculator.

The one shown here was found on eBay and was fully working (for once!). It just needed some cleaning

The eBay purchases luckily came with all the associated documentation and boxes which is unusual. I also have the original calculator case (not shown).