|Re: And they multiply like rabbits ...|
Message #4 Posted by Ellis Easley on 9 Apr 2002, 1:42 a.m.,
in response to message #3 by rsenzer
I also like the TI34. I hadn't noticed the similarity to the HP6S, now I see every key is the same! Does this mean even TI is using an off-the-shelf chip - or does it mean all the others are using a TI chip, making TI's domination even greater than is obvious?
What had struck me about the TI34, when I first saw it recently, is that it must be where HP got the idea for some of the styling of the HP30S, at least the graphics molded into the sliding cover.
In an effort to answer my own first question, I used my new miniature screwdriver set to open my HP6S and TI34 (not 34C). I should have realized that the IC dice would be bonded directly to the printed circuit boards and covered with blobs of epoxy. The only particular similarity I can see is that both calculator chips have a connection to the + power source, and a capacitor from the + source to another pin (not the other supply lead), to provide either a power-on-reset or an oscillator or a substrate supply bypass. That's all the parts there are on the HP6S; the TI34 has another capacitor (maybe because it is solar only) and -
A very interesting thing on the TI34 is an LED next to the IC (covered by the case). It is a flat leaded package aiming across the surface of the PCB. The main axis of the LED would be below the seam on the side of the calculator, between the "STO" and "RCL" buttons. The LED plastic is pink, suggesting to me it is probably an infrared LED. Because of my background in diagnostics, I imagine the LED is there to output diagnostic information during testing, and infrared LEDs are the most efficient.
As to how to put the chip into test mode, it might be through direct connection to some test pads, but if that is the case, and a bed-of-nails fixture is being used, why not get the output that way as well? I remembered that an engineer at Tandy had a patent on a way to transmit information on an AC power line, not a modulated carrier method like carrier current transmission (like X-10) but a baseband method that assumes you have complete control of the power source. He did the work in a effort to automate the giant light displays on Tandy's "twin towers" headquarters (which the new Radio Shack corporation recently sold). The two 20 story buildings have arrays of lights on two sides which are used to display things like "Radio Shack", "United Way", and at Christmas time, the color images of candles. The lights are changed by hand and the only animation is blinking lights to make the candles twinkle. But the engineering department (the original one, not the one that did the computers) had developed a way to automate the lights by providing an addressable microprocessor to control each light. Information would be transmitted by dropping individual cycles or half-cycles from the AC power, using zero-crossing solid-state relays, I presume. So this might be the way the TI34 is put into test mode. Assuming that extensive testing is only being done once, on the complete assembly, they might be using an LED to illuminate the solar cell to power the unit, and then pulse the LED off to input information. I have some amber LEDs made for road signs which are incredibly bright with only 20-30 mA, I'm sure they would power the calculator. This sounds like a great experiment!
Regarding solar-only calculators, I happened to look at a Radio Shack calculator made by Casio (I think the Casio's with aluminum bezels and little plastic keys are some of the prettiest calculators, although they are confusing to use), this was a "dual power" calculator and its little lithium battery had expired just sitting in the box. I looked in the "Tandyized" booklet to see if it said what battery to use - another "dual-power" Casio I have names the battery number although it says it is not user-replaceable (meaning you need a screwdriver to do it). The Tandy booklet said you can't replace the battery, but you can keep using it as a solar-only after the battery dies. This may be a case of Tandy's natural inclination to sell an expensive battery being overridden by Tandy's need to avoid liability if a salesman tried to change the battery. If anybody remembers "DeskMate" which Tandy shipped with many pre-Windows PCs, including in ROM in some early laptops - and which was a major project inside Tandy and was very Windows-like by the time development stopped - it was explained to me that the main reason Tandy wanted DeskMate, which was a basic integrated utility, was so that the sales people would have some Tandy-owned software to run while demonstrating the computers. Obviously, training the people to use one suite of software was an advantage, but the greater purpose was that the alternative would be to use commercial software like Lotus 123 to demo the machines, and if there were open packages of commercial software in the stores, the sales people would be tempted to give customers bootleg copies to make a sale, exposing Tandy to an unacceptable liability.
Anyway, I found that by removing the dead battery from the Radio Shack/Casio calculator altogether, it went from working sluggishly to working crisply. I like solar-only's because sometimes when they turn on they have intersting junk on the display or in the memory. Like when things go wrong on TV.