Month: April 2009

Electronics Workbench, Machine Shop

Laser Pointer Annoyances

Laser pointer battery contact
Laser pointer battery contact

Maybe it’s just me, but all of the laser pointers I’ve bought, even the relatively spendy ones, have crappy switches and unstable battery contacts.

For example, this is the business end of a $12 (!) pen-style pointer. The battery contact was off-center and poorly secured; I pried the white plastic retainer out, bashed the spring into submission, and replaced the retainer with a length of heat-shrink tubing. It wasn’t pretty.

This pointer has an actual mechanical switch module inside, with a clicky mechanism actuated by the external button. Cheaper pointers seem to rely on bare PCB contacts bridged by the button’s base. Ugh.

Laser pointer battery orientation: positive DOWN
Laser pointer battery orientation: positive DOWN

Memo to Self: The AAA cells fit into the housing with the positive terminal away from the laser head. The white plastic plug has a molded cross that could be mistaken for a + symbol, but it’s not.

Administrivia, Oddities

Favorite Spam Comments

Most folks seem content to read my scribblings without commenting, which is OK with me. After all, I rarely comment on the blogs I follow, so turnabout seems only fair play.

Some of you offer sage advice and suggestions, which I greatly appreciate.

And then we have the spammers…

A few spam comments have poked my Amusement button and I finally decided it’s time to collect the better ones. A short list begins there and should (slowly, I hope) grow over time.

Administrivia

Mandatory Setup Slide for All Presentations

Presentation Setup Slide
Presentation Setup Slide

When you put together a presentation, add this slide at the very end.

Display it while you’re setting up the projector so you can make sure all the corners are on-screen, all the colors work, and that the circles are actually circular. Your audience will appreciate your consideration.

The text font should be whatever you’re using for the main body text in the presentation. If you think the text I’ve used is too large, then you’ve never sat in the back of your own presentation…

When you’re ready to start, whack the Home key and your regular title slide will appear.

Here it is as a single-slide PowerPoint presentation, because WordPress doesn’t allow uploading OpenOffice ODP presentations. Copy the slide into your own file and let your audience move around accordingly.

Machine Shop, Recumbent Bicycling

Tour Easy: Fitting Novara Transfer Bike Panniers

Mary recently replaced her well-worn REI packs with a pair of Novara Transfer panniers, chosen because they’re just about the biggest packs available without insanely specialized world-touring features. They seem rather less rugged than the older ones, so it’s not clear how long they’ll last.

They fit her Tour Easy recumbent fairly well, but there’s always a bit of adjustment required.

Ramp on front edge of lower clamp rail
Ramp on front edge of lower clamp rail

She hauls tools and clothing and veggies to & from her gardens, food from the grocery store, and the Token Windows Laptop to presentations. She brings the packs inside, rather than leave them on the bike, so they get mounted & dismounted for every ride.

The packs hang from the top bar of the rear rack, with a sliding clamp near the bottom of the pack that engages the rack’s vertical strut. I adjusted the clamp to the proper fore-and-aft position, but we found that the front end of the rail holding the clamp jammed against the seat support strut. That’s not a problem found on a diamond-frame bike.

The top picture shows the solution: Mr Pack, meet Mr Belt Sander. A ramp chewed onto the front end of the rail lets it slide neatly over the strut and all is well. The only trick was to avoid sanding through the pack fabric: the line perpendicular to the rail is sanding dust, not a gouge!

Acorn nut caps inside pack
Acorn nut caps inside pack

Each top rack hanger mounts to the plastic pack frame with three bolts covered by plastic acorn nuts on the inside; the acorns cover actual metal nuts, so it’s a lot more secure than it looks. Three more bolts secure the bottom rail to the frame, with three more acorns poking into the pack, for a total of nine acorn nuts.

Most folks carry clothing and suchlike in their packs, so the 10 mm bump at each acorn presents no problem. Unfortunately, those things look like a nasty bruising hazard for soft veggies and groceries.

Top hanger pad - outside view
Top hanger pad - outside view

I sliced up some closed-cell foam packing material (everybody saves some of that stuff, right?), punched holes at the appropriate locations, and tucked the pads over the acorns. An inner fabric layer covering the frame and nuts should hold the pads in place.

Bottom pads with hole punch
Bottom pads with hole punch

It’s not clear the bottom pads will stay in position, but I wanted to try this without adhesives, mostly because I doubt any adhesive can secure polyethylene foam to whatever plastic the pack frame is made from or coated with. Perhaps double-sided foam tape will work?

Top pad - with tools
Top pad - with tools

So far, the early reviews are good …

Electronics Workbench, Oddities

Capacitor Plague Up Close

A friend dropped off a dead eMachines Celeron for my next recycling trip. Peering inside, what do my wondering eyes behold but a nasty case of Capacitor Plague!

Herewith, some pix of the victims within the box. Note the bulging tops ready to blow along the pressure-relief grooves, the distinct tilt caused by the bulging bottom plug, and the right-hand cap near the power supply on countdown for launch!

More background on the plague is there.

I must build an ESR tester one of these days…

PC Tweakage

Backup with Rsnapshot

Now that our low-budget file server (a stock Dell Inspiron 531S desktop with an additional 500 GB SATA drive) is up & running Xubuntu 8.10, it’s time to get rsnapshot working again.

All our data files live on the server, so the backup routine need not handle any of the usual /home stuff on our desktop boxes. Rebuilding a dead box is a nuisance, but they’re all pretty much the same and it’s less of a nuisance not worrying about rare failures… haven’t had any failures in many years; they get replaced before they die.

The backup files go to an external 500 GB USB drive, which is not protection against a catastrophe in the basement. Mostly, this guards against finger fumbles; the external drive gets dumped to another hard drive in the fireproof safe more-or-less monthly.

So. To begin…

Install rsnapshot, which will also drag in ssh, the metapackage around the client & server sides of openssh. The server side is already installed so I can sign in using public-key authentication.

Set /etc/rsnapshot.conf thusly (comments snipped out):

snapshot_root   /mnt/backup/snapshots
no_create_root  1
cmd_cp          /bin/cp
cmd_rm          /bin/rm
cmd_rsync       /usr/bin/rsync
cmd_ssh /usr/bin/ssh
cmd_logger      /usr/bin/logger
cmd_du          /usr/bin/du
cmd_rsnapshot_diff      /usr/bin/rsnapshot-diff
#interval       hourly  6
interval        daily   30
#interval       weekly  4
interval        monthly 12
#interval       yearly  1
logfile /var/log/rsnapshot
du_args -csh
backup  /mnt/userfiles/         oyster/
backup  /mnt/bulkdata/          oyster/
backup  /mnt/music/             oyster/
backup  /mnt/diskimages/        oyster/

Basically, that creates a month of daily backups, plus monthly backups for a year. Haven’t ever gotten to a yearly backup, but you get the idea.

The no-create-root option prevents horrible things from happening if the USB drive wakes up dead and doesn’t mount; you don’t want to back up the drives to the /mnt/bulkdata mount point. The USB drive mounts using a UUID entry in /etc/fstab, as described there.

Create a pair of scripts in /root to mount the USB drive, do the backup, unmount it, and shut down the system:

rsnapshot.daily

#!/bin/sh
logger "Mounting USB drive"
mount /mnt/backup
logger "Starting backup"
/usr/bin/rsnapshot daily
logger "Unmounting USB drive"
umount /mnt/backup
logger "Power off"
shutdown -P now
logger "Done!"

rsnapshot.monthly

#!/bin/sh
mount /mnt/backup
/usr/bin/rsnapshot monthly
umount /mnt/backup
shutdown -P now

Note: the rsnapshot executable has moved from /usr/local/bin in Ubuntu 7.10 to /usr/bin in 8.10.

You could be more clever than that, but, eh, they’re simple & easy.

The Inspiron 531S 1.0.13 BIOS now powers off dependably with the 2.6.27-14-generic kernel in 8.10, a pleasant change from the 1.0.12 BIOS and the 2.6.22-16-generic kernel used in 7.10. That means the shutdown commands work and I can shave 25% off the server’s power bill. Not that it’s very big to begin with, but every little bit helps.

Set up /etc/crontab to run the backups (and sync the system clock with reality, for the reasons described there):

10 23	1 * *	root	/root/rsnapshot.monthly
30 23	* * *	root	/root/rsnapshot.daily
#
00 01	* * *	root	ntpdate north-america.pool.ntp.org

And that’s it.

Memo to Self: add e2fsck to the monthly backup routine and move it an hour earlier.

PC Tweakage

Ubuntu 8.10 Server Setup: Samba

We need Samba for the Token Windows Laptop and the CNC box on the milling machine which also runs TurboTax during that season of the year. Despite having done this many times before, it never works right until, suddenly, without warning, everything works. It’s a permission thing, I think.

To get SWAT running, check there, which boils down to:

  • sudo chmod g+w /etc/samba/smb.conf
  • sudo chgrp adm /etc/samba/smb.conf

Put this in /etc/xinetd.d/swat:

... comments snipped ...
service swat
{
        port    = 901
        socket_type     = stream
        wait    = no
###     only_from = localhost
        user    = <<your adm-enabled userid>>
        server  = /usr/sbin/swat
        log_on_failure  += USERID
        disable = no
}

Then use sudo smbpasswd -a -e <> to set up the allowed users and get their passwords aligned. I use the same userids and paswords on all the boxes, which is terrible security.

Whenever you change anything, use sudo /etc/init.d/samba restart to make sure Samba gets the message.

Use SWAT to set up all the shares. This is what the config file looked like after the damn thing finally started working:

# Samba config file created using SWAT
... snippage ...

[global]
	workgroup = whatever-you-use
	server string = %h server (Samba, Ubuntu)
	map to guest = Bad User
	obey pam restrictions = Yes
	passdb backend = tdbsam
	pam password change = Yes
	passwd program = /usr/bin/passwd %u
	passwd chat = *Enter\snew\s*\spassword:* %n\n *Retype\snew\s*\spassword:* %n\n *password\supdated\ssuccessfully* .
	unix password sync = Yes
	syslog = 0
	log file = /var/log/samba/log.%m
	max log size = 1000
	dns proxy = No
	usershare allow guests = No
	panic action = /usr/share/samba/panic-action %d

[printers]
	comment = All Printers
	path = /var/spool/samba
	create mask = 0700
	browseable = Yes
	printable = Yes
	writeable = Yes

[print$]
	comment = Printer Drivers
	path = /var/lib/samba/printers

[Bulkdata]
	comment = Assorted useful files
	path = /mnt/bulkdata
	read only = No

... likewise for other file shares ...

Actually, you don’t have to share the printers with Samba. Better to use CUPs directly. Just tell Windows to “Connect to a printer on the Internet or on a home or office network”, then fill in something like:

http://oyster:631/printers/R380_TP

And that’ll work even better.