Recently in Computing Category

Adafruit Proto Cape Kit for Beagle Bone

I bought one of Adafruit's Proto Cape Kit for my Beagle Bone Black so that I could put 3 relay circuits and pin headers on it. The double-sized PCB is supplied with separate pin headers that you have to solder on yourself.

It provides access to all of the pins but only SYS_5V is provided as a set of power lines and not VDD_5V, so limited current is available. However, this doesn't matter too much given that there is very little space for components.

I had to really squash everything in and use a lot of wires because there was no chance of creating an optimal layout:

Visible power button

My new server case doesn't have a very visible power button and I don't want the reset button being pressed instead... some careful application of white correction fluid makes it easier to see:

Before (indented black power symbol) After (indented white power symbol)

Bluetooth

Three different eBay sellers have all sold me USB Bluetooth adapters (at costs varying from very-cheap to brand-name-premium) with duplicate addresses*. I'm currently waiting for the third one to stop ignoring the law (and me) so that I can return the most recent purchase.

I was ready to give up and decide it was now impossible to buy genuine Bluetooth devices that comply with the Bluetooth Specification when I tried purchasing some Belkin adapters from Amazon, and it turns out that despite the increased cost these actually have unique addresses.

* Bluetooth adapters with duplicate addresses means that if you happen to be using your adapter within range of someone else who got theirs from the same manufacturer's batch, you'll get conflicts accessing devices because there will be two devices on the network with the same address. Avoid Dynamode and cheap unbranded devices.

RS232

Every cheap "Serial to USB" adapter I can find uses a PL2303 chip with active low signaling, which isn't the same as a real PC serial port. Fortunately FTDI sell real adapters. The US232B has 9V high, -9V low outputs and its inputs are open low at 0V.

Scanners

I recently bought a scanner, although it's not new... because scanner manufacturers are completely ignoring non-Microsoft users. Newer hardware isn't supported in Linux because the scanner chips (provided by separate companies) are different and no one thought to provide drivers for other operating systems. Older hardware is supported but is no longer being sold, so instead of the original manufacturer making a profit from sales to new customers, people selling used hardware gain instead.

Even the older hardware isn't supported by the manufacturer itself, instead third-party developers contributing drivers to the SANE project provide the only way of using these devices. (Which is probably a good thing as actual manufacturer drivers are likely to be closed source).

Unfortunately newer models of scanner hardware doesn't actually provide anything new. Scanning a 300 DPI image at 4800 DPI only makes the resulting image data larger (and most likely makes it less usable as minute details of the paper/film grain will become visible). With no reason to buy such hardware and develop drivers for it, these will go unsupported until the used hardware is no longer available.

So I now have a Canon CanoScan LiDE 60. I'd link to it but there's no longer a page for it on Canon's website. As far as I can tell this is currently the only bus-powered high-speed USB scanner supported under Linux (except perhaps the LiDE 50). The (latest) drivers for it aren't available for 64-bit versions of Windows (just like my TV receiver cards... there is a pattern developing here).

Line art scans of documents can be compressed very well, which is useful for the mountain of old bits of paper that I should throw away...

Motorola doesn't provide any way to install new root certificates for Java (despite there being an interface to install them for SSL) and the only root certificates installed other than their own is the lucrative "Java Verified" monopoly certificate.

Fortunately it is possible to insert your own root certificates, such as the one provided by CAcert who issue free code signing certificates.

  1. Add the certificate to /ezxlocal/download/appwritecmsec/.policy/._policy.txt:
    CA Cert Signing Authority (anything)
    2
    1
    MIIHPTCCBS... (root certificate)
    0
    0
    0
    0
    This will make it appear in the list of Java Root Certificates under Security Settings. That's all it does. The following two files are actually used by the JVM.

  2. Add the certificate to /ezxlocal/download/java/.policy/._policy.txt:
    domain: C=;L=;O=Root CA;OU=http://www.cacert.org;CN=CA Cert Signing Authority
    2
    1
    AAAcHBwcHB... (copy this from the UTI certificate)
    MIIHPTCCBS... (root certificate)
    FrUyG9TH8+DmjvO90rA67rI5GNE= (unknown)
    1049027389 (start date)
    1995712189 (end date)
  3. Add the certificate to /usr/securesetup/.policy/_devdomain.txt:
    domain: CA Cert root certificate (anything)
    type: 2
    rootcert: MIIHPTCCBS... (root certificate)
    allowchangestatus: 0
  • Where the root certificate is specified, it's in DER format and Base64 encoded all on one line.
  • I copied the unknown part in the second policy file from the UTI certificate and it was automatically updated for me (including the domain DN).
  • Somehow /ezxlocal/download/java/.policy/._hmac.txt was not world readable, which is required to run the MIDlet from the menu.


Using signed MIDlets, I can finally set some of the permissions to "Never Ask" and avoid irritating prompts.

MIDlet certificate information

Network Speakers

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I had an unused Mini-ITX computer which I can make silent (by removing the fan) as long as it isn't doing anything too intensive, and some spare speakers from a broken CD player... so I put together some remote speakers to play music on.

With some cheap bamboo cane and tie wraps I've mounted them at the head of my bed. The server boots over the HomePlug network allowing MPD to connect to it. I'll add a wireless remote control soon.

Speaker frame Speakers at top of bed Remote speaker server

NTP reference clocks

I've finally finished putting together the parts to connect multiple NTP reference clocks to the same serial port...

[Inside of box]

It uses three reference clocks - one GPS receiver and two radio clocks (DCF77 and MSF).

[MSF receiver]

[DCF77 receiver]

[GPS receiver]

New server

It's close to two months since I decided to replace proxima's aging hardware and two returned motherboards later I finally moved everything over on friday. It's much faster.

It's also been snowing tonight... started soon after I left for Tesco :/.

New Printer and Young Boy

My new printer is here... but it doesn't come with a USB cable so I can't use it yet :(

ASDA are selling young boys for £5!

About this Archive

This page is an archive of recent entries in the Computing category.

California is the previous category.

Consumer Products is the next category.

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Content authored by myself is just my honest opinion. If you find any words or pictures menacing or offensive, stop reading now.

Jabber

simon@arlott.org.uk
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