HP

64 Articles

A Modern Take On A Piece Of Old Test Equipment

December 15, 2019 by No comments

The HP 11947A is something of a footnote in the back catalogue of Hewlett Packard test equipment. An attenuator and limiter with a bandwidth in the megahertz rather than the gigahertz. It’s possible that few laboratories have much use for one in 2019, but it does have one useful property: a full set of schematics and technical documentation. [James Wilson] chose the device as the subject of a clone using surface mount devices.

The result is very satisfyingly within spec, and he’s run a battery of tests to prove it. As he says, the HP design is a good one to start with.   As a device containing only passive components and with a maximum frequency in the VHF range this is a project that makes a very good design exercise for anyone interested in RF work or even who wishes to learn a bit of RF layout. At these frequencies there are still a significant number of layout factors that can affect performance, but the effect of conductor length and  stray capacitance is less than the much higher frequencies typically used by wireless-enabled microcontrollers.

Patch, Or Your Solid State Drives Roll Over And Die

December 10, 2019 by 117 Comments

Expiration dates for computer drives? That’s what a line of HP solid-state drives are facing as the variable for their uptime counter is running out. When it does, the drive “expires” and, well, no more data storage for you!

There are a series of stages in the evolution of a software developer as they master their art, and one of those stages comes in understanding that while they may have a handle on the abstracted world presented by their development environment they perhaps haven’t considered the moments in which the real computer that lives behind it intrudes. Think of the first time you saw an SQL injection attack on a website, for example, or the moment you realised that a variable type is linked to the physical constraints of the number of memory locations it has reserved for it. So people who write software surround themselves with an armoury of things they watch out for as they code, and thus endeavour to produce software less likely to break. Firmly in that arena is the size of the variables you use and what will happen when that limit is reached.

Your Drive Is Good For About 3 Years And 9 Months

Sometimes though even developers that should know better get it wrong, and this week has brought an unfortunate example for the enterprise wing of the hardware giant HP. Their manufacturer has notified them that certain models of solid-state disk drives supplied in enterprise storage systems contain an unfortunate bug, in which they stop working after 32,768 hours of uptime. That’s a familiar number to anyone working with base-2 numbers and hints at a 16-bit signed integer in use to log the hours of uptime. When it rolls over the value will then be negative and, rather than the drive believing itself to be in a renewed flush of youth, it will instead stop working.

Egg on the faces of the storage company then, and an urgently-released patch. We suspect that if you own a stack of these drives you will already know about the issue and be nervously pacing the racks of your data centre.

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Where Did Pocket Computing Start?

October 2, 2019 by 36 Comments

A smartphone in 2019 is an essential piece of everyday equipment. Many of you are probably reading this page on one, and it will pack a very significant quantity of computing power into your hand. Pocket computing has a long history stretching back decades before the mass adoption of smartphones though, and Paleotronic has an interesting retrospective of that earlier history.

The piece starts with the Radio Shack PC-1, a rebadged Sharp with a calculator-style keyboard and a one-line alphanumeric LCD display, then continues through the legendary TRS-80 Model 100 to the era of the palmtop. It’s a difficult subject to cover in its entirety as there are so many milestones on the pocket computing path, but it’s an interesting read nevertheless as it successfully evokes the era when a 300 Baud connection via an acoustic coupler was a big deal. We might for example have mentioned the Atari Portfolio if only for its use by a young John Connor to scam an ATM in Terminator 2, and as any grizzled old sysadmin will tell you, there was a time when owning a Nokia Communicator might just save your bacon.

Of the classic pocket computing devices mentioned, only one has received significant coverage here. The TRS-80 model 100 still has a huge following, and among quite a few hacks featuring it we’ve seen one brought into the smartphone age by getting the ability to make a cellular connection.

TRS-80 Model 100 image: Jeff Keyzer from Austin, TX, USA [CC BY-SA 2.0]

Tearing Apart Pulse Transformer Switches

June 3, 2019 by 29 Comments

If you like mechanical keyboards, you like switches. Historically, switches were weird, with strange capacitive rubber dome switches in Topre boards, buckling springs in the IBM Model M, and beamsprings in earlier IBM keyboards. This teardown of an HP signal generator has the weirdest keyboard switches ever. They’re being called pulse transformer switches, but they are the strangest, weirdest, and most complicated keyboard switch we’ve ever seen

Mechanically, these keys are mounted on a 1×5 plastic frame with a plunger that presses down on a (brass?) photoetched plate. Mechanically, this is effectively a metal dome keyboard that simply presses a springy bit of metal against a contact on a printed circuit board. That’s the mechanical explanation, the electrical theory of operation is much, much weirder.

Electrically, this keyboard consists of a printed circuit board with two coils underneath each key. The circuit is wired up so two keys are ‘read’ at the same time with a pulse from a multiplexer. This pulse induces a current in the ‘sense’ coil of two individual keys which is sent to a comparator. If both keys are not pressed, the comparator sees a positive and a negative voltage which cancels out, meaning no keys are pressed. If one key is pressed, the metal dome shorts out the transformer underneath the keyboard, meaning only one voltage is seen by the comparator, and that key is registered as being pressed.

This is some crazy keyboard circuitry, and I do not say that lightly. There are ‘acoustic’ keyboards out there which consist of a row of keys striking a metal bar with an acoustic transducer on each end. By measuring the time it takes for the sound of a keypress to reach either end of the metal bar, a keypress can be registered. This is weird and expensive to build, and it’s still simpler than a pulse transformer switch. Check out the video below.

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Plot Your Way Past A Tiny Buffer

May 18, 2019 by 15 Comments

There is a dedicated community of plotter enthusiasts who keep their often-aging X-Y axis pen drawing devices going decades after they were built, and who share plotter-generated paper artwork online. [Dhananjay Balan] was seduced by this, so acquired a second-hand HP7440A through eBay and set about bringing it to life.

Bringing it to life was in the first instance the usual progression of cleaning the mechanism and checking all was in order, before doing a bit of research to find that the missing power supply was a 10-0-10V AC item. Then some adapters and a USB-to-serial port had it talking to a modern PC, and thanks to the wonders of HPGL it was working once more. This could thus have been a very simple tale worthy of the dreaded Not A Hack moniker, had the focus then not changed from the hardware into the software.

Back in the day, a 60-byte buffer in a plotter must have seemed huge. But in 2019 a plotter can be sent data at a rate that will swiftly fill it, after which the commands are not stored and are never drawn. Introducing a delay between sending commands solves the problem, but at the expense of very slow plotting. This was solved with a very clever use of the HPGL command to send the pen position, which waits until the pen has finished moving before sending its return value. This became a handy way to detect when the plotter was ready for more, allowing speedier printing without buffer overruns.

The plotter has an expansion port into which an optional module containing trigonometric drawing functions could have been plugged, but was missing in this example. HP’s idea was that the buffer was so small that a programmer would have difficulty writing their own, but the buffer hack in the previous paragraph put paid to that. Python code for all this and more is in a handy GitHub repository.

Via Hacker News.

Restoring An HP LCZ Meter From The 1980s

April 7, 2019 by 11 Comments

We are fantastically lucky not only in the parts that are easily available to us at reasonable cost, but also for the affordable test equipment that we can have on our benches. It was not always this way though, and [NFM] treats us to an extensive teardown and upgrade of a piece of test equipment from the days when a hacker’s bench would have been well-appointed with just a multimeter and a 10MHz ‘scope.

The Hewlett Packard 4276A LCZ meter is, or perhaps was, the king of component testers. A 19″ rack unit that would comfortably fill a shelf, it has a host of functions and a brace of red LED displays. This particular meter had clearly seen better days, and required a look inside just to clean up connectors and replace aged batteries.

In the case is a backplane board with a series of edge connectors for a PSU, CPU, and analogue boards. Aged capacitors and those batteries were replaced, and those edge connectors cleaned up again. The CPU board appears to have a Z80 at its heart, and we’re sure we spotted a 1987 date code. There are plenty of nice high-quality touches, such as the individual 7-segment digits being socketed.

An after-market option for this equipment included a DC offset board, and incredibly HP publish its full schematic and a picture of its PCB in their manual. It was thus a simple process and quick PCB ordering to knock up a modern replica, with just a few component substitutions and single resistors replacing an HP specific encapsulated resistor pack.

As a treat we get a ringside seat for the set-up and alignment of the machine. The DC offset board gives the wrong voltage, which he traces to a voltage reference with a different tolerance to the original HP part. [NFM] makes some adjustments to resistor values, and is able to pull the voltage to the correct value. Finally we see the instrument put through its paces, and along the way have a demonstration of how capacitance of a ceramic capacitor can vary with voltage close to its working voltage. Even if you never have the need for an LCZ meter or never see an HP 4276A, this should be worth a watch. And if you now have an urge to find a bench full of similar treasures, take a look at our guide to old test equipment.

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Let’s Look At Some Cool Old LEDs

December 14, 2018 by 17 Comments

LEDs are now a mature technology, with all manner of colors and flavors available. However, back in the 1970s, it was early days for this fledgling display tech, and things looked very different. [IMSAI Guy] happened to work at the optoelectronics division of Hewlett-Packard during their development of LED displays, and has a handful of prototypes from those heady days.

The video is a great look at not only vintage display hardware, but also rarely seen prototypes that seldom left the HP offices. Matrix, 7-segment and even 16-segment devices are all in attendance here. There’s great macro photography of the packages, including the now-forgotten bubble displays as well as hermetically sealed glass packages. The parts all have a uniquely 1970s look, drenched in gold plating and otherwise just looking very expensive.

The followup video breaks out the microscope and powers up the displays. [IMSAI Guy] shares some useful tips on how to best tinker with unknown LED parts, as well as knowledge about the chemical compounds and manufacturing processes involved in LED production. If you don’t know your III-V compounds from your II-VI compounds, prepare to learn.

It’s always interesting to take a look back, and even better to get a peek at the experiments of engineers of the past.

If you’re wondering about applications of this hardware, we’ve seen messageboards and watches before. Video after the break.

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