Category: Home Ec

Things around the home & hearth

Driveway Drain Pipe Grate vs. Chipmunks

Known to be true: chipmunks love drain pipes!

Chipmunk peering from drainpipe

Obviously, an open pipe attracts rodents.

That didn’t matter with a three-foot pipe attached directly to the downspouts, but, as part of the driveway project, I routed the house storm drains and wall footing drain pipes about 20 feet down from the new retaining wall, with the two joining into a single outlet. There’s a cleanout plug on the storm drain line, but the footing drain consists of about 50 feet of corrugated and perforated tubing that would be just about the finest possible chipmunk habitat.

In principle, one would simply glue a grate into the final fitting and be done with it, but leaves from the gutter will pack behind the grate, so it must be removable. Leaving the grate loose means it’ll pop out at the slightest provocation and, most likely, roll another hundred feet down the driveway into the street.

Rather than coping with that, I drilled a clearance hole in the elbow and tapped a matching hole in the grate:

Drain pipe grate – hole tapping

I have a few white nylon 1/4-20 cutoffs from the bike fairing clamps, so I wrecked the threads on one and jammed it into a black nylon thumbscrew:

Drain pipe grate – thumbscrew

Now, of course, the critters can still climb down the drainpipes from the gutters and set up housekeeping in the plumbing, but I’m not putting grates where I must climb onto the roof to clear them. A chipmunk dropped from two stories will scamper away; I’d never walk again.

We shall see how this works out…

2013-01-28
Hall Effect Sensors From eBay: Variations On a Specification

It seems that the “49E” Hall effect sensor I used to measure the field in the ferrite toroid was running at 1.9 mV/G, rather than the 1.0 to 1.75 range suggested by the perhaps-not-quite-applicable specs. Here’s a table of all the sensors in my collection, which came in two bags from the usual eBay vendors:

Seq 49E 231NB AH49E

1 41.1 18.5

2 42.9 20.0

3 39.5 19.9

4 40.6 18.8

5 43.3 18.9

6 42.6 23.0

7 40.7 20.0

8 44.0 19.3

9 18.9

10 19.5

11 20.0

12 19.8

That’s the RMS value in mV of the sine wave resulting from a 200 mA peak current in the 25 turn winding, measured on the scope with low pass filtering and 8 trace averaging. An unfiltered and unaveraged trace looks like this, which explains why I’m knocking back the noise:

Hall Current Sense – 25T FT50-61 – raw

Even with that noise reduction, the variation between successive readings is about 5%, so trust only the first digit and half of the second; the fractional digit is worthless. Averaging the columns gives 42 and 20 mV RMS, which correspond to 59 and 28 mV peak. I estimated 60 mV peak from the filtered-but-not-averaged scope trace in the earlier calculations, which falls in the same ballpark. If you were doing this for real, you’d use a DC current and a static field, plus a simple RC filter to improve the noise rejection, but this was a quick-and-dirty measurement.

The peak magnetic flux should be about 31 to 33 G; I’ve been using 32 G based on the nominal permeability and measured air gap. Assuming that’s the case, then the sensors in the first column run at 1.8 mV/G (1.75 + 3% or 1.7 + 6%) and those in the second column at 0.875 mv/G (1.0 – 9%).

Here’s what I think: these are manufacturing rejects, sold cheap to extract money from suckers. Those in the first column came from the “too high” scrap heap, the second column’s contestants were in the “too low” pile. Note the tight clustering: they’re not random, they’ve been carefully selected! A quick-and-dirty histogram tells the tale:

49E Hall Effect Sensor Histogram – 200 mA 32 G

The nominal range, taken from the SS49E datasheet, runs neatly across the gap in the middle, with one sensor falling just barely inside. The SS49 range neatly brackets the data on the left, but that’s not what those parts are supposed to be.

Now, I’ve often referred to eBay as my parts locker (at least for stuff I don’t have in the Basement Laboratory Warehouse Wing), but I know what to expect and am not in the least surprised at these numbers. If you or anyone you know buys parts from eBay in the expectation that they’re getting Good Stuff Cheap, then you should rethink that expectation.

I’d say that, to a very good first approximation, anything bought directly from halfway around the planet via eBay (or any source like it) will be, at best, counterfeit. For my purposes, I can measure and use most of it (assuming it actually works and ignoring minor issues like, oh, reliability and stability). In an actual product application, eBay is not the way to get your parts.

No surprise, right?

I wonder what the supply current might be? They’re supposed to run around 6 mA, max 10 mA…

2013-01-24

Improved OXO Can Opener Knob

We recently replaced a defunct can opener with an OXO opener that removes can lids without creating razor-sharp edges. Unfortunately, the knob doesn’t agree well with Mary’s hand, so I laid out a prototype doorknob-shaped cap (and also removed all the can lids that confronted her):

It prints in four parts: the flat cover and three pillars, with two filament snippets aligning each pillar. The internal openings of this model do not fit the OXO knob’s lobes correctly; a Dremel sanding drum worked wonderfully well to make it fit. The next version should have much smaller pillar bases with a bit more clearance at the top: measurements from the as-adapted pillars will be in order.

Gluing everything together once again justifies having Too Many Clamps:

OXO Can Opener - gluing knob cover — OXO Can Opener – gluing knob cover

I intended to secure cap to knob with 2-56 screws in those recessed holes and even went so far as to flatten the top of the knob’s lobes in preparation for drilling:

OXO Can Opener - knob flats — OXO Can Opener – knob flats

However, Dragorn of Kismet gave me a few packets of only slightly outdated Sugru (a great idea that’s far too spendy and short-lived for my shop) that solved the problem:

OXO Can Opener - knob cover with silicone tape — OXO Can Opener – knob cover with silicone tape

The silicone tape wrap greatly improves the griptitude.

Early returns indicate this works reasonably well, but the top should be more rounded and tapered. It goes without saying that black filament would be much less ugly…

The OpenSCAD source code, with the caveat that the as-printed knob won’t fit without considerable abrasive adjustment:

// OXO Softworks Can Opener
//  Enlarged & rounded knob
// Ed Nisley KE4ZNU December 2012

include </mnt/bulkdata/Project Files/Thing-O-Matic/MCAD/units.scad>
include </mnt/bulkdata/Project Files/Thing-O-Matic/Useful Sizes.scad>

// Layout options

Layout = "Cap";
                    // Overall layout: Build1 Build2
                    // Parts: Cap Knob

//- Extrusion parameters must match reality!
//  Print with +1 shells and 3 solid layers

ThreadThick = 0.25;
ThreadWidth = 2.0 * ThreadThick;

HoleWindage = 0.2;

function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

Protrusion = 0.1;           // make holes end cleanly

//----------------------
// Dimensions

TriLobeRad = 37.5;					// radius: center to end of lobe
TriLobeOD = 2*TriLobeRad;
TriLobePeakRad = 23.0;				// radius: center to peak height
TriLobeHeight = 22.5;

WingArcRad2 = 48;					// Arc between knob lobes, top
WingArcRad1 = WingArcRad2 - 5;		//
WingArcOffset = 14.0;				// Knob center to arc2 radius

KnobOD1 = 70;						// maximum dia without chamfer
KnobOD2 = 65;						// top dia

KnobSides = 3*4;					// maintain 3-side symmetry

DomeHeight = 8;						// dome shape above lobes

KnobHeight = DomeHeight + TriLobeHeight;

DomeOD = KnobOD2 + (KnobOD1 - KnobOD2)*(DomeHeight/KnobHeight);

DomeArcRad = (pow(KnobHeight,2) + pow(DomeOD,2)/4) / (2*DomeHeight);

ScrewDia = Tap2_56;
ScrewHeadDia = Head2_56;
ScrewBase = 0.6*DomeHeight - Head2_56Thick;

AlignPinDia = 3.0;
AlignPinCircleRad = 0.55*(WingArcOffset + KnobOD2/2);
AlignPinDepth = 3.0;

//----------------------
// Useful routines

module PolyCyl(Dia,Height,ForceSides=0) {           // based on nophead's polyholes

Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

FixDia = Dia / cos(180/Sides);

cylinder(r=(FixDia + HoleWindage)/2,
         h=Height,
         $fn=Sides);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

    Range = floor(50 / Space);

    for (x=[-Range:Range])
        for (y=[-Range:Range])
            translate([x*Space,y*Space,Size/2])
            %cube(Size,center=true);

}

//-------------------
// Component parts

module TriKnob() {
	intersection() {
		difference(convexity=3) {
			translate([0,0,-Protrusion])
				cylinder(r=TriLobeRad,h=(TriLobeHeight + 2*Protrusion));
			for (i=[-1:1])
				rotate(i*120)
					translate([(WingArcOffset + WingArcRad2),0,-TriLobeHeight/2])
						cylinder(r1=WingArcRad1,r2=WingArcRad2,h=2*TriLobeHeight);
		}
		translate([0,0,TriLobeHeight/2])
		cube([2*KnobOD1,2*KnobOD2,TriLobeHeight],center=true);
	}
}

module KnobCap() {
	difference() {
		intersection() {
			translate([0,0,(KnobHeight-DomeArcRad)])
				rotate(180/KnobSides)
					sphere(r=DomeArcRad,$fa=180/KnobSides);
			difference(convexity=4) {
				rotate(180/KnobSides)
					cylinder(r1=KnobOD1/2,r2=KnobOD2/2,h=KnobHeight,$fn=KnobSides);
				TriKnob();
			}
			rotate(180/KnobSides)
				cylinder(r1=KnobOD2/2,r2=KnobOD1/2,h=KnobHeight,$fn=KnobSides);
		}
		for (i=[-1:1])
			rotate(i*120) {
				translate([-TriLobePeakRad,0,0]) {
					PolyCyl(ScrewDia,KnobHeight);
					translate([0,0,TriLobeHeight + ScrewBase])
						PolyCyl(ScrewHeadDia,KnobHeight);
				}
			}
		for (i=[-1:1]) for (j=[-1,1])
			rotate(i*120 + j*(270/KnobSides))
				translate([AlignPinCircleRad,0,(TriLobeHeight - AlignPinDepth - Protrusion)])
					PolyCyl(AlignPinDia,2*(AlignPinDepth + Protrusion));
	}
}

//----------------------
// Build it!

ShowPegGrid();

if (Layout == "Cap")
	difference() {
		KnobCap();
		cylinder(r=KnobOD1,h=Protrusion/2,center=true);
	}

if (Layout == "Knob")
	TriKnob();

if (Layout == "Build1")
	translate([0,0,-TriLobeHeight])
		difference() {
			KnobCap();
			translate([0,0,(TriLobeHeight - Protrusion)/2])
				cube([2*KnobOD1,2*KnobOD2,TriLobeHeight+Protrusion],center=true);
		}

if (Layout == "Build2")
	translate([0,0,TriLobeHeight])
		rotate([180,0,0])
			difference() {
				KnobCap();
				translate([0,0,(TriLobeHeight + TriLobeHeight/2)])
					cube([2*KnobOD1,2*KnobOD2,TriLobeHeight],center=true);
			}

2013-01-14

Credit Union vs. Credit Karma vs. Account Security: FAIL

You know how you’re supposed to not click on email links these days, even when they’re from “trustworthy” sources, because you might be a spear-phishing target? Well, here’s a true story about how our Credit Union handles the situation.

The backstory: I recently signed up for a service that provides an estimate of my credit score, which it does by asking the usual Big Three credit reporting agencies for my records on, presumably, a monthly basis. I’m not happy with that arrangement, but I wanted to see how well it worked and figured I’d cancel after a month or two. Based on these exchanges with their support staff, it’s time to cancel…

After I received the expected email from them, I discovered that the only way to reach the service was through an embedded link. I try to avoid doing that sort of thing, so I went directly to (what I assumed was) their website and tried to log in. That didn’t work, so I fired off a support message…

From me to CreditKarma:

Having signed up for your service through the Hudson Valley Federal Credit Union, it seems that I cannot sign on directly to your site using the email address and password I provided during the HVFCU signup.

That means the only way to sign on to my account requires clicking on the link provided in your monthly email, which redirects me through the HVFCU website.

Is that correct?

If so, how can I distinguish your email from a well-designed spear phishing attack that requires me to divulge two banking userids and passwords?

Thanks…

Their reply, which neatly avoids answering the questions:

Sorry for the confusion. Your HVFCU Credit Karma account is different from any account you may have created with www.CreditKarma.com. To log into your HVFCU Credit Karma account, you’ll first need to log into your online banking account and then log in through there.

But that’s not how it works:

OK, so I must go through the HVFCU website to reach you. That process seems to require cookies set by the redirection included in the email link, because simply signing on to the HVFCU website and clicking the appropriate link does not redirect to your website unless I have already followed the email link.

So, allow me to ask the key questions again:

The only way to sign on to my account requires clicking on the link provided in your monthly email, which redirects me through the HVFCU website.

Is that correct?

If so, how can I distinguish your email from a well-designed spear phishing attack that requires me to divulge two banking userids and passwords?

Please answer those questions, as I need to know how this works.

Thanks…

There’s been no answer after a week, so I think I’ve reached the end of their tech support.

Then I posed much the same question to the Credit Union:

Having recently signed up for the CreditKarma score monitoring service, I’m flabbergasted by the total lack of security awareness.

The only way to access the CreditKarma report is through the link in the monthly email. Clicking that link requires signing in to my HVFCU account, then to the CreditKarma account.

Without that clicking on that link, selecting the “Credit Score” menu item in the HVFCU site does nothing.

Without clicking on that link, the CreditKarma.com website does not recognize my email address.

How, exactly, can I distinguish that monthly email from a well-crafted spear phishing attack that will collect the userid and password for both of my accounts?

Is there an alternate procedure for accessing my CreditKarma account that does not require depending on a lengthy link contained in an email message?

Thanks…

Their reply seems slightly more informative, but note that they ignore the “must click the link” evidence I report and also avoid answering the hard questions:

I regret to hear of the difficulties you are experiencing with Credit Karma. If you would like to access the site directly, you should type: https://hvfcu.creditkarma.com. The https: indicates that the connection will be secured. “creditkarma.com” lets you know that you are connecting to Credit Karma’s web site. hvfcu. is the subdomain created by Credit Karma for HVFCU members. Your account will not work at http://www.creditkarma.com because the subdomain created for HVFCU is separate from their public site.

Additionally, you may also log on to Internet Banking, then click on the “My Credit Score” link near the top right of the page, and you may now log in. If you chose this option, ensure that all pop up blocker settings are adjusted since you will be required to access a separate web page. Clicking on the link in the monthly emails will direct you to the same place. We understand that you may not be comfortable clicking on a link or may be using a system or mobile device that doesn’t allow you to view the link, which would make it difficult to determine if a message was legitimate or fraudulent. In these cases, we recommend that you set a shortcut or favorite for https://hvfcu.creditkarma.com or else sign in to Internet Banking first, then click on the “My Credit Score” link.

So I tried again:

> Your account will not work at http://www.creditkarma.com because the subdomain created for HVFCU is separate from their public site.

Indeed, it doesn’t. When I asked them about that, their reply was, shall we say, unhelpful; they really want me to click on the link and didn’t even mention the HVFCU subdomain. I did tell them that I had an HVFCU account, so they weren’t completely ignorant of the situation.

They have not responded to my question about determining whether an email allegedly from them is a phishing attack, either.

> Additionally, you may also log on to Internet Banking, then click on the “My Credit Score” link near the top right of the page, and you may now log in.

As I reported, that doesn’t work unless you’ve previously clicked on the email link to set whatever tracking cookies they use. I’ve tried it immediately after clearing cookies and cache: it doesn’t work. Clicking on the link to bounce off their website sets everything up properly and then the HVFCU menu item works.

Try that and see how it works for you. I’d like to know whether it’s a peculiarity of Firefox and Chrome.

> We understand that you may not be comfortable clicking on a link

As the HVFCU page on phishing says: “Links within the email take you to a fake website that usually looks authentic because it uses graphics from the institution’s real website.” So, basically, I must regard all clickable links in all emails as suspect.

Given that the URL is total gibberish, with the both the HVFCU and Credit Karma URLs buried within tracking numbers, there’s no possibility of manually extracting and typing the address.

So, as I asked originally, please tell me exactly how I can tell that an email purporting to be from Credit Karma isn’t a very well-done phishing attack?

We both know there’s no way to do so, so why do you and Credit Karma rely on email links for such a vital function? You’re training your customers to click on emailed links, which is a terrible security practice for a bank.

Have you documented the direct sign-on process anywhere your customers can find it? I couldn’t, but maybe I’m not looking in the right place. Why not put those instructions in each email, rather than using clickable links?

Thanks…

Another week has passed, so I suspect they’re not going to answer those questions, either.

Am I the only person who thinks it’s bad practice for a bank to require you to click on emailed links?

2013-01-08
Wall Switch Failure

Here’s what happens to a really old wall switch:

Wall Switch – innards

A closeup of that broken contact:

Wall Switch – detail

This switch controlled an outlet, so I’m sure it’s hot-switched far too many vacuum cleaners, clothes irons, and suchlike over the last half century or so.

Our house is a bit fancier and originally had top-of-the-line mercury-wetted switches: the contacts sealed in the capsule don’t burn, but the springy supporting structures outside the capsule eventually wear out.

They’re still more reliable than X10 switches, though.

2013-01-07
Furnace Heat Exchanger: Temporary Repair

Which small spot on this hot-air furnace heat exchanger isn’t like all the other small spots?

Pinhole in furnace heat exchanger

Correct! The orange one at the corner of the rectangular exhaust gas flue that’s lit up like the sun, because you’re looking directly into the oil burner flame.

With the fire off and everything cooled down, it looked like this:

Pinhole in furnace heat exchanger – detail

Now, this calls for a new furnace (because replacing the heat exchanger costs as much as a new furnace), but as it turns out this was in an unoccupied house during the week before Christmas. So I scrubbed off the debris with a steel brush, bent up a snippet of 2 mil brass shimstock to fit the corner, applied a layer of JB Industro-Weld epoxy to the problem, and positioned 200 W of incandescent bulbs to help it cure slightly sooner than forever:

Furnace heat exchanger – temporary fix

That is most certainly not a final repair, not just because the heat exchanger’s normal operating temperature exceeds the epoxy’s 500 °F rating, but because where there’s one pinhole there’s bound to be more. The goal was to let us keep the furnace running until we could schedule the replacement after the holidays. Remember, the building isn’t occupied and neither of the smoke / CO detectors went off at any point in the proceedings.

Houses are trouble!

2013-01-06
HP3970 Scanjet Lid Hinge Repair

When the second hinge on my father-in-law’s scanner broke, he asked if I could fix it:

HP3970 Scanjet Lid – broken hinge

It’s a flatbed scanner, so the lid is nearly 18 inches long and weighs 2.2 pounds with the slide / negative backlight illuminator. The stress raiser notches, located exactly where the cracks started, look like a perfect example of how not to do these things.

I solvent-glued the hinges back together, with a square brass tube applying clamping force to the joint overnight, but this certainly won’t last for long:

HP3970 Scanjet Lid – crude repair

HP used to have some really smart engineers, but this looks like it was done by a Newkid (I was one, once, so I know the type) after a solid modeling and simulation session convinced him that those two thin plastic webs had enough strength for the job.

No. They. Do. Not.

Of course, HP provides no Official Way to repair that failure, as the hinges emerge seamlessly from the injection-molded plastic lid frame: you must scrap the scanner and buy a new one, because the lid would cost more than a new scanner. Equally of course, the fact that they don’t have a Windows driver beyond XP makes replacement a foregone conclusion.

It runs under Xubuntu 12.04, mostly, which is what I set him up with after the XP PC got compromised.

2013-01-04