Category: Everything Else

Papilio One Xilinx FPGA breakout board

This week, I came across the Papilio One FPGA board. This intriguing board mounts a Xilinx Spartan 3E, in either the 250K or 500K gate flavor, along with power supplies and an on-board USB programmer.  It’s inexpensive, at $50 for the 250K version and $70 for the 500K version. This would make a good pre-assembled alternative to the Microsemi SOC (née Actel) A3PN250 breakout board I am using.

One really neat feature of the Papilio is that it is designed to be Arduino-compatible! By loading an AVR8 soft core onto the FPGA, Arduino-compatible sketches can run on the board. The board supports a set of connectors to which up to 6 expansion boards (“wings”) can be attached, similar to shields. Its inclusion of a programmer and power supply also imitate the Arduino model.  As well as Arduino programs, the board is also programmable in Verilog and VHDL.

Unlike my board, its off-board connections are through-hole, and it can’t be mounted directly on a ground plane without extra insulation.  I like the philosophy of bringing out a full 48 uncommitted pins to the off-board connectors instead of loading up the board with extras.  Boards with RAMs, flash, and displays are easy to get started with, but end up being confining, making it harder to add external circuitry when the on-board stuff is not enough.

The Papilio is a close relative of the Open Bench Logic Sniffer, designed by Ian Lesnet and Jack Gassett. The Papilio heritage shows in the Logic Sniffer’s two “wing” expansion connectors.

If your FPGA preference is Xilinx or if you want a flexible, basic breakout board with an on-board programmer and power supply, the Papilio is well worth a look.

Crazy PCB Layout from the Big Hair Decade

Check out the bizarre PCB layout on this power supply.  A Pulse Instruments PI-702, I bought it for a few dollars at a hamfest. It was made in the mid-80’s and plugs into Tektronix TM500-series mainframes. When I powered it up, BANG!, after which it had no output.  Here is what I found when I opened it up for a look:

The curvy, hand-taped traces are typical for the period, but look at how few components are in the two-thirds closest to the front panel compared to the number of pads! Plenty of those pads look like they have an 0.3″ DIP pattern, but have either discretes or nothing soldered to them.  The layout is also full of dead-ends and traces that don’t go anywhere, and there is no silkscreen.  The back third is neat and tidy — it is all a bit Dr. Jekyl and Mr. Hyde.

All of this leaves me wondering what the crazy layout is for! If it is meant to dissuade reverse-engineering, it might work (it worked for me, so far…), but who would want to protect something as simple as a linear power supply? It is even stranger that the digital-to-analog conversion circuitry near the edge connector gets so little of the board, and is laid out quite cleanly compared to the power supply.  I suppose that this might be a case of multiple models using a single PCB, but what a devious mind it would take to merge multiple schematics into something that looks like this!

The problem itself was easy enough to find. One electrolytic capacitor dried out and blew up. You can see it at the lower-left of the second photo. It will be easy to fix, assuming it didn’t take any other components with it.

The device itself is interesting.  It has three outputs, two of which are bipolar, each covering -25 V to +25 V continuously. They can be independently set with front panel controls, track an external input, or be controlled digitally. The bipolar outputs are limited to a wimpy 25 mA each, which is undoubtedly why it is called a bias supply. It also has a fixed +5 V output at up to 0.5 A.

Now I know that the 80’s were not only the decade of MTV and big hair, but at least one rather strange PCB layout.

Farewell, Digi-Key catalog

The May 2011 High Frequency Electronics arrived with the sad news that the most recent Digi-Key catalog is the last, replaced by the www.digikey.com web site.  Digi-Key are also cancelling their TechZone magazine.

I suppose it was inevitable. The warning signs were certainly there, as Digi-Key sent thinner and less frequent catalogs to hobbyists than to professionals, then cut back  to annual issues. Nevertheless, I will miss the giant catalog that has always had a prominent place in my office and home lab.

I received my first Digi-Key catalog in 1983. Back then, it was thin, only 32 or 64 pages long. They had a good optoelectronics section, which remains one of their strengths. The only US semiconductor manufacturer they carried was National Semiconductor, though they distributed several lines of Japanese semiconductors.  (At one point, I wondered if National was Japanese, too!) Continue reading “Farewell, Digi-Key catalog”

Cleaning the Basement: When Junque is just Junk

I don’t know who coined the term “junque”, but it used to be used on the QRP-L mailing list to describe questionable treasures brought home from a hamfest. “But honey, it’s not junk, it’s high-class junque!”  Like many engineers, I’m a bit of a packrat for old parts and gear, and there was a time in my bachelor life when I saw it as my duty to rescue as many old HP and Tektronix instruments as I could, especially the tube variety. Call it a misplaced attempt to emulate the Endangered Species Act.

My wife has quietly tolerated my electronics junk in the basement, but my life has moved on. I have two children, and my sense of what I’m doing in my hobby has crystalized. Now I look at a basement full of stuff and think, “Boy, it would be nice to have a rec room here.”

This week, I went on the warpath and started cleaning. I started with the shelves under the basement stairs, which were packed full of “treasures”. Among them I found these endangered species:

Three HP antiques
Left to Right: HP 400D vacuum-tube voltmeter, HP X-Y plotter, HP 211A square wave generator

Continue reading “Cleaning the Basement: When Junque is just Junk”

Texas Instruments buys National Semiconductor

Surprise news this morning: Texas Instruments is buying National Semiconductor for $6.5 billion.  National is strong in power and analog chips. Many of the jellybean op amps and voltage regulators we have all used came from National, whether directly or via copies sold by other companies.  TI is strong in just about everything: general analog, specialty and high-performance analog, digital signal processing, logic, microcontrollers, and so on. Continue reading “Texas Instruments buys National Semiconductor”