The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Author: Ed

Halogen Blinky Test

Dropping the ordinary flashlight bulb into the drawer where it belonged revealed what I think is a halogen flashlight bulb, so I rebuilt the blinky test setup:

Halogen flashlight bulb test setup

This time I used a BUZ71A MOSFET (13 A, 100 mΩ RDS) driven with a 10 V gate pulse to make sure it acted like a switch instead of a current sink.

The first attempt looked … odd:

Halogen 3V – no cap – 4ms 1A-div

The gate pulse is yellow, the drain voltage is magenta, the bulb current is cyan at 1 A/div, and the timebase ticks along at 2 ms/div.

Moving the magenta trace to the supply voltage on the other side of the bulb produces even more weirdness:

Halogen 3V – no cap – Vsupply – 4ms 1A-div

Apparently, slugging a 3 A bench supply with a 3 A pulse lasting only 4 ms causes distress of the output tract.

Kludging a hulking 22 mF (yes, 22000 µF) cap across the power supply provides enough local storage to make things work properly:

Halogen 3V – 22000µF – Vsupply – 4ms 1A-div

With the cap in place, the drain terminal looks less unruly:

Halogen 3V – 4ms 1A-div

The drain voltage starts at about 600 mV with the 3 A pulse, a bit more than you’d expect from the alleged 100 mΩ drain-source resistance, but those numbers are generally aspirational and the test setup leaves a lot to be desired.

A 10 ms pulse produces a distinct flash, rather than a dull orange blip (timebase now at 10 ms/div):

Halogen 3V – 22000µF – 10ms 1A-div

A 30 ms pulse reaches full brightness as the filament settles at normal operating temperature:

Halogen 3V – 22000µF – 30ms 1A-div

A 20 ms flash might suffice for decorative purposes, in which case each pulse requires 90 mW·s = 3 V × 1.5 A × 20 ms of energy. Running it all day requires 7.8 kW·s = 2.2 W·h, so it’s even less appealing than that old skool tungsten bulb.

Which is, of course, why LED flashlight bulbs are a thing.

2021-12-07
Incandescent Blinky Test
A flashlight bulb emerged from the clutter, which prompted me to ask if it might make an interesting blinky. Spoiler: probably not.

The bulb had “2.4 V 0.7 A” stamped on its shell, so the test setup looked like this:

Flashlight bulb test setup

A list seems helpful:
- Solder wires to bulb in lieu of a socket
- Bench supply at 2.4 V
- Grossly abused 2N3904 NPN transistor as a switch
- Function generator pulsing the base
- Scope voltage probes on base (yellow) and collector (magenta)
- Tek current probe on bench supply lead (cyan, 500 mA/div)
The function generator has a 50 Ω output, so depend on it to limit the base current just like it was a resistor. The output voltage is symmetric around 0 V, so apply an offset of half the peak-to-peak signal to get a positive-going pulse:

Flashlight bulb test – function gen setup

A 150 ms pulse gives the bulb just barely enough energy to light as a little orange blip, with the collector voltage dropping as the filament heats up and its resistance increases:

Tungsten 2.4V 700mA – 150ms

Given 350 ms to heat up, the bulb produces a nice white-hot flash:

Tungsten 2.4V 700mA – 350ms

The poor transistor acts as a 600 mA constant current sink, which isn’t surprising given its 300 mA absolute maximum current rating.

Homework: figure the base drive and current gain

Protip: don’t do that to a cherished transistor

The bulb resistance starts out at 0.5 Ω and rises to 2.5 Ω when the filament glows white-hot at the end of the pulse.

Something like 250 ms produces a noticeable blink, requiring 360 mW·s = 2.4 V × 600 mA × 250 ms from the power supply. Blinking once every ten seconds all day means 8640 pulses for a total energy of 864 mW·hr; call it 1 W·hr.

A pair of (fresh) AA alkaline cells provide 7.5 W·hr for maybe a week of blinkiness.

A not-dead-yet 18650 lithium cell might offer 15 W·hr, but running the bulb from 3.7-ish V, rather than 3-ish V, increases the energy per pulse by 20% and decreases the run time correspondingly.

Surely not worth the effort …
2021-12-06
Humana Unsubscribe FAIL

Quite some years ago, I had a health insurance plan with Humana, although I gave it up because the premiums seemed entirely disproportional to the benefits. They have continued to bombard me with emails telling me how wonderful they are, with an obligatory sentence at the bottom:

If you do not want us to contact you by email, you can unsubscribe from our online Humana community.

I do not know anything about this “community” of which they speak, other than that they seem to think I want to be part of it.

Clicking on the “unsubscribe” link takes me to a page at their randomly named email service, whereupon I check the “don’t send me anything” box and click the “Submit” button:

Humana Unsubscribe failure

Did you see the green text near the middle, where my email address should be? Apparently somebody misconfigured the email script to not include the actual address; the %25 gibberish seems to be encoded percent signs, so it may be one of those too-many / too-few / wrong-kind of character escapes.

Just a typo that could happen to anyone. Right?

Having once been a customer, I still have an account, but there is no way to control / shut off those messages. Not being a current customer, however, I cannot use their chat interface, which would likely not be productive. I am unwilling to wait on hold for an hour, because I know my call is not valuable to them, and their customer service rep wouldn’t be competent to solve the problem anyhow.

Fortunately, I can set up a filter to route their emails directly to trash.

2021-12-03
Walker Leg Shortening

While looking for something else, Mary came across a walker in the attic and mentioned that, if she ever had to use it, the shortest position of the adjustable legs would put the hand grips too high for comfort. Maybe they

Well, I can fix that:

Walker shortening – hole indexing

The holes are an inch apart, so I clamped the V blocks parallel to the X axis on the drill press, zeroed the X axis knob, slid the leg to get the drill bit into the last hole, clamp in place, crank the table an inch, then use a step drill to start the hole:

Walker shortening – hole drilling

The holes are just slightly larger than the 1/4 inch step on the drill, so the twist drill cuts them to size.

A tubing cutter sliced an inch off all four legs and all four frame tubes:

Walker shortening – latch relocation

The white plastic fitting in the frame tube prevents the legs from rattling, but I had to drill another hole to move the latch button, too.

With a bit of luck, we’ll never need the thing.

2021-12-02
Simple Pliers Rack

A Round Tuit™ finished this trivial project:

Long-handle pliers rack

Yeah, it’s just seven pairs of holes drilled with a 5/8 inch Forstner bit in a scrap 2×4, which was then introduced to Mr Belt Sander to peel off the dust of ages.

There’s a spare set of holes in front because I’m absolutely certain that, without them, another pair of pliers would suddenly pop into existence on the bench.

2021-12-01
Incandescent Bulb Lifetime: Also Better Than Average

This bulb spent the last seven-plus years of its life lighting the front bathroom:

Dead incandescent bulb – 7 years

The green corrosion around the tip seems strange, given that we don’t use the tub or shower in that bathroom, and I’m pretty sure it wasn’t the cause of the failure.

My stock of incandescent bulbs will eventually run out; I must figure out how to light the deaders in an attractive manner.

2021-11-30
Lyme Disease, Now With Bonus Babesiosis

Two weeks of doxycycline should kill off all the Borrelia bacteria responsible for Lyme disease, but a blood test shows the antibodies:

Lyme test – 2021-11-10

Those antibodies will gradually disappear during the next few months and, unfortunately, a past Lyme infection does not prevent future infections.

The tick also injected Babesia parasites which do not respond to antibiotic treatment:

Babesia test – 2021-11-10

The “titer” refers to the dilution required to produce a negative test result, with the 1:64 reference titer representing six successive 50% dilutions. My blood required ten 50% dilutions to produce a negative result for the IgG antibodies and (presumably) six 50% dilutions from a 20% base for the IgM antibodies.

As I understand the situation, IgM antibodies appear promptly upon infection and IgG antibodies follow along later, so my reaction to the Babesia infestation was ramping up after two weeks.

In the Bad Old Days™, quinine was the go-to treatment for parasitic infections, but it has a host of horrific side effects at the dosage required for traction against actual diseases; tonic water ain’t gonna get you where you need to go.

The new hotness is atovaquone, arriving as 100 ml of a yellow liquid with the consistency of latex paint, (allegedly) the taste of “tutti fruitti“, and a price (modulo your drug plan) making inkjet printer ink look downright affordable. You might expect to get a 5 ml measuring spoon along the the bottle, but suffice it to say it’s an exceedingly good thing I’m well stocked for printer cartridge refilling.

All of the diseases and drugs list “fatigue” / “drowsiness” / “malaise” as symptoms / side effects and I’m here to tell you knocking off a couple of hours in the recliner during the day does nothing at all to disturb another nine hours in the sack overnight.

A few weeks of low productivity in the Basement Shop™ will definitely count as a successful outcome.

Protip: We need permethrin spray. Lots permethrin spray.

2021-11-24