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A Two-Arm Monitor Stand for the Raspberry Pi

Two Arm Mount on Steampunk Table-Cropped-500 Wide.jpg

If what I’ve heard is true, most Raspberry Pi installations consist of the naked circuit board lying atop a nest of wires on the desk behind a monitor. I think it’s true; that was certainly my Raspberry Pi installation for a long time. Now, I’ve decided to use my steampunk computer table as my Raspberry Pi 3 workstation. And I got an idea: Use one of those VESA-standard 2-arm monitor stands that clamps to the edge of a desk without any drilling into or other hacking-up of the desk. One arm holds the monitor, and the other holds the Raspberry Pi itself.

The trick is to buy one of several Raspberry Pi cases that includes a flange with VESA 75 or VESA 100 holes. VESA is a standard for TV and monitor mounting hardware. Its two smallest configurations are a 75mm square, and a 100mm square. Most modern flat-panel TVs and many monitors have threaded holes on their back faces arranged in one of the several VESA configurations. I’m pretty sure (having looked at a lot of monitors and TVs in the past few years) that the 100mm configuration is the commonest. It’s the one on the Dell 1907fp monitor that I’ve been using for Raspberry Pi boards since the beginning. VESA-compatible displays generally use metric screw threads in the mounting holes, with M4 the standard for the smaller configurations, including 100mm. M4 screws can be had at Ace Hardware, and probably also at Home Depot and Lowe’s. (I go to Ace first for such things.)

The Raspberry Pi case that I used is this one:

RPi VESA Case.jpg

It has four little wings with both the VESA 75 and VESA 100 holes. The holes in the wings aren’t threaded, and easily pass standard 8-32 machine screws, which I used to hold the case to the second arm of the monitor stand. I oriented the Raspberry Pi with its USB ports on top, so I can reach over the monitor and plug in peripherals or thumb drives easily.

This approach isn’t limited to the Raspberry Pi. There are VESA cases for the Intel NUC (Next Unit of Computing) boards, and most of the higher-end embedded boards like BeagleBone. On a small table like the one I made, there’s not a lot of flat space to park a case of any size, so whatever computer I’m going to be using on it should be able to hang on that second monitor arm. The arms on the unit I bought can hold up to 12 pounds each. Most of the small-form factor Dell machines I use are that weight or lighter. Dell’s Micro 3000 series has an optional VESA bracket, and brackets for other models may be available. And hey, you guys could rig something, right?

Odd Lots

  • I had some fairly sophisticated oral microsurgery about ten days ago, and it kind of took the wind out of me. That’s why you’re getting two Odd Lots in a row. I have things to write about long-form but have only recently found the energy to write at all. Promise to get a couple of things out in the next week.
  • Some researchers at UW Madison are suggesting that sleep may exist to help us forget; that is, to trim unnecessary neural connections in order to improve the signal-to-noise ratio in the brain. Fair enough. What I really want to know (and am currently researching) is why the hell we dream. I doubt the answer to that is quite so simple.
  • Ultibo is a fork of FreePascal/Lazarus that creates custom kernel.img files for the Raspberry Pi, allowing direct boot into an embedded application without requiring an underlying OS. I haven’t tried it yet (still waiting on delivery of a few parts for a new RPi 3 setup) but it sounds terrific. Bare metal Pascal? Whoda thunkit?
  • Humana just announced that it is leaving the ACA exchanges after 2017. As I understand it, that will leave a fair number of counties (and some major cities) with no health insurance carriers at all. Zip. Zero. Obamacare, it seems, is in the process of repealing itself.
  • NaNoWriMo has gone all political and shat itself bigtime. You know my opinions of such things: Politics is filth. A number of us are talking about an alternate event held on a different month. November is a horrible month for writing 50,000 words, because Thanksgiving. I’m pushing March, which is good for almost nothing other than containing St. Patrick’s Day. (Thanks to Tom Knighton for the link.)
  • Paris has been gripped by rioting since February 2…and the US media simply refuses to cover it, most likely fearing that it will distract people from the Flynn resignation. Forget fake news. We have fake media.
  • I heard from a DC resident that there was also a smallish riot in Washington DC today, and so far have seen no media coverage on it at all.
  • Cold weather in Italy and Spain have caused vegetable shortages in the UK. Millions of small children who would supposedly never know what snow looked like may now never know what kale looks like. Sounds like a good trade to me.
  • Trader Joe’s now sells a $5 zinfandel in its house Coastal brand, and it’s actually pretty decent. Good nose, strong fruit. Seems a touch thin somehow, but still well worth the price.
  • I don’t know if you’ve ever seen Gahan Wilson’s cartoons in Playboy and National Lampoon, but Pete Albrecht sent me a link to an interview with Wilson that explains why he did certain things the way he did, like his brilliant series called “Nuts” about how the world looks and feels to small children.

Odd Lots

Odd Lots

Odd Lots

Odd Lots

Measuring Raspberry Pi USB Power Draw

Smartronix USB Meter.jpg

Most of the problems that turn up while configuring Raspberry Pi systems cook down to inadequate power. The infamous stuttering keyboard problem vanished immediately here when I put the RPi on a stiffer 5V supply. When I bought a second RPi for a programming system, I incorporated a powered hub capable of sourcing 500 ma from each port, and in doing so strangled the power problem in its crib.

Problem solved, but I still wondered: How much juice do these things actually need? How stiff is the 5V supply? I’m a bench tech, and not being able to do actual measurements made me nuts. So I sniffed around a bought a test instrument for measuring voltage and current at a USB port under load. It’s the Smartronix USB Power Monitor, model ST034TT05-01-001. I bought it from CyberGuys; $49.95.

It works like any current meter: You connect it between a USB port and a USB device. It simultaneously measures the voltage on the port and the current through the device. There’s a full-size Type A jack on the right side of the box for connecting the load, and a full-size AB cable plugging into a B jack on the left side of the box, which plugs into a Type A port.

Works like a charm. I did the measurements below in about ten minutes:

Raspberry Pi board running Raspbian, w/o Wi-Fi 50-73 ma
Dell 0C8639 wired USB mouse 5-17 ma
Dell SK8135 wired USB keyboard 53-56 ma
AirLink AWLL5088 Wireless N Ultra Mini USB Wi-Fi 32-80 ma
SanDisk Cruzer Mini thumb drive, 256 MB 27-30 ma
SanDisk Cruzer Micro Skin thumb drive, 256 MB 75-89 ma
San Disk Cruzer Mini thumb drive, 512 MB 7-11 ma
KingMax Super Stick thumb drive, 512 MB 35-62 ma
SanDisk Cruzer Mini 1 GB thumb drive, 1 GB 5-11 ma
SanDisk Cruzer Micro Skin thumb drive, 4 GB 75-91 ma
SanDisk Cruzer Micro Skin thumb drive, 8 GB 43-70 ma

In the readings above, the two numbers are the range across which I saw current run. In most cases, the first number is when the device is idle, the second is when it’s busy. All measurements were taken from the same USB port, one of the four ports on the Rosewill powered hub. All devices tested are USB 2.0, because the meter itself is not listed as capable of testing USB 3 devices.

I have several of most of the thumb drives, and identical models were almost alike in their power behavior. This made me wonder how the Cruzer Minis managed to use so little power while doing the same task that all the other drives did. In this case, the task was copying a 109 MB file (the Lazarus 1.0.6 installer) from the PC to the thumb drive. One would think that smaller drives would draw less current, but not so.

Probably the biggest eyebrow-raiser was how rubbery the 5V USB rail is on my quadcore. An 8GB Cruzer Micro Skin thumb drive pulled the port down from 4.99 v to 4.91 v while drawing 90 ma. The same drive pulled the Rosewill hub supply down by only .02 v , from 5.17 v to 5.15 v while drawing 70 ma. (Current draw in thumb drives is not the same on the RPi as it is on Windows.)

My only gripe about the meter is that “peak” mode displays the highest values for voltage and current, when voltage and current generally move in opposite directions as load increases. So a downward movement in voltage isn’t registered in peak mode.

Other than that, it works as described and answered a whole lot of questions about what sorts of things I can reasonably expect to connect to a Raspberry Pi’s built-in USB ports. Actually, I now recommend using the powered hub for everything, given the RPi’s touchiness about power. It makes the RPi system bulkier and snakier, but a whale of a lot more reliable.

And as for the Smartronix USB power meter, let’s say solidly (if not quite highly) recommended.

Odd Lots

Odd Lots

Odd Lots

  • Yes, I’ve been away from Contra for longer than I’d like, and the Odd Lots have been piling up. Some of that away was necessary for my sanity, and was spent by the pool at a resort in Phoenix, where Carol and I discussed things like the wonder of a single-celled organism that is 10 cm long. The secret appears to be evolving superior organelles. Bandersnatchi, anyone?
  • While I was gone, someone released a new OS for the Raspberry Pi: The Pidora Remix. It’s basically Fedora for the Pi. I haven’t tried it yet, but I’ll flip another SD card out of the drawer soonest and burn an image. Man, you have to run like hell just to stay in one place in this business.
  • The Raspberry Pi’s main competition, the BeagleBone, now has a 1 GHz ARM Cortex A8 version that ships with a Linux 3.8 kernel. BeagleBone Black supports the Linux Device Tree, which does a lot to decouple hardware details from the kernel. Looks terrific–now all it needs is an installed base.
  • I noticed a system resource draw-down when I had iTunes installed on my old and now electrocuted quadcore. The software took a lot of cycles and memory, even when it didn’t appear to be doing anything. The discussion has come up on Slashdot. (The poster also mentioned Rainmeter, which I tried once and found…ok.) I try to run a lean system here, and I frown on things that want services, tray icons, and 15% of my cycles all the damned time. (The Dell Dock does precisely that. For showing a row of icons. Sheesh.)
  • Amazon is setting up a new markeplace for short fiction, with a twist: It offers to share revenues on fan fiction with the authors of the original items. It’s unclear how many authors will accept that, but I would, like a shot. (I guess all I’d need are some fans.) In truth, Jim Strickland and I talked in detail some years back about opening up the Drumlins World to all authors who’d care to tell a story there, without even asking for money.
  • Clinical depression may be linked to sleep cycles, which appear to have a genetic basis. How to fix this is unclear, but I’ll testify that depression in the wake of losing Coriolis laid waste to my sleep habits for a couple of years. (Thanks to Jonathan O’Neal for the link.)
  • The Man Who Ploughed the Sea may soon be mining it…for uranium. I’d cut to the chase and just mine it for gold, so I can buy more ytterbium for my Hilbert Drive. Alas, there’s less gold in the oceans than we thought (1 part per trillion) and not much more ytterbium (1.5 parts per trillion) so maybe I should just extract the uranium (3 parts per billion) and make yellow pigments to sell on Etsy.
  • I’m not sure I buy this, but it’s an interesting speculation: That the Younger Dryas cold snap was triggered by a smallish asteroid that crashed…in Lake Michigan. Click through for the maps if nothing else. My favorite Great Lake is deeper and more complex than I thought.
  • Save the apostrophe’s! (From a fate worse than dearth…)
  • And save us, furthermore, from new Microsoft technology that counts people in the room watching your TV. Because having more than one person watching a TV show or movie rental is…is…stealing!
  • 3-D printing is still in the stone age (and the Old Stone Age at that) but if we don’t allow berserk patent law to strangle the kid in its crib, wonderful things will happen once 3-D printers are no longer CNC glue guns. (Thanks to Pete Albrecht for the link.)
  • I’m starting to think that 3-D printers like that will soon make one-off repro of small plastic parts like the ones at the center of kites practical. I guess the challenge is somehow getting the precise shape of the part into a file. If I weren’t trying so hard to be a novelist I would probably have a 3-D printer already. For the moment I’m glad I didn’t jump as soon as I otherwise might have.
  • Speaking of CNC…and guns: Plastic guns are dumb, dangerous, ineffective, and basically a stunt that seems designed (probably in Autocad) to make politicians say stupid things and make enemies. The real issue is cheap, portable CNC machines capable of cutting metal. That horse is out of the barn and beyond the horizon.