Astable Multivibrator: DSO150 vs. Capacitor Voltage
Posted by Ed in Electronics Workbench on 2019-01-22
With the astable blinking green, I had to do this:
It blinks every two seconds because it uses 1 MΩ timing resistors, rather than the 2 MΩ resistors in the first version.
Because the DSO150 runs from the internal battery, you can clip it anywhere with few ill effects. The blinky runs from a battery, too, but connecting a high-impedance node to what’s basically the power line common may lead to heartache and confusion; it’s generally a Bad Habit.
A closer look at the DSO150 screen shows the expected bipolar exponential waveform across the 1 µF timing cap:
The scope triggering seems iffy, as the trace capture pauses every now and again for no apparent reason. This may have something to do with the very slow sweep speed; at 500 ms/div, the complete waveform takes forever to accumulate.
At least we know the signal lies well within the DSO150’s bandwidth!
Encrypted Email: What Could Possibly Go Wrong?
So this arrived from an email address similar to, yet not quite the same as, the URL of a physician’s office where I had an appointment a few days hence:
My email client is set to prefer plain text, disallow remote content, and not open attachments, so that’s as far as it got. Donning asbestos work gloves and face mask, I pried open the message and its attached HTML file with the appropriate tools and found, as expected, scripts doing who-know-what.
Called the office and, also as expected, was told my appointment time had been changed.
Showed up, mentioned it to the doctor, and was told the office must check off many boxes to demonstrate its HIPAA compliance.
Bottom line: HIPAA now requires patients (a.k.a., us) to open random attachments from random senders, all in the name of privacy.
Banks do that, too.
Tea Strainer: Tare Weight
Being a responsible consumer, I carefully measure my daily green tea dosage. A laser-cut stainless steel strainer and silicone steam cap recently arrived, with a most auspicious tare weight:
Before my Genuine IBM 5160 PC XT with an 8088 CPU, I scratch-built a Z80 “personal computer” and wrote a primitive multitasking OS. Plenty of electrons have flowed through the transistors since those days.
A great way to start the day; ya can’t make this stuff up!
Hawk vs. Squirrel
Judging from the squirrel tracks on both sides of the scuffle, the squirrel lived to tell the tale:
I think the squirrel came in from the right, the hawk stooped from a pine tree on the left and missed the catch, whereupon the squirrel departed leftward as fast as its little paws could go.
Surely a hair-raising encounter!
Tensilizing Copper Wire
Posted by Ed in Electronics Workbench, Machine Shop, Science on 2019-01-18
The “bus bars” on the battery holders are 14 AWG copper wire:
Slightly stretching the wire straightens and work-hardens it, which I’d been doing by clamping one end in the bench vise, grabbing the other in a Vise-Grip, and whacking the Vise-Grip with a hammer. The results tended to be, mmm, hit-or-miss, with the wires often acquiring a slight bend due to an errant whack.
I finally fished out the slide hammer Mary made when we took a BOCES adult-ed machine shop class many many years ago:
The snout captured the head of a sheet metal screw you’d previously driven into a dented automobile fender. For my simple purposes, jamming the wire into the snout and tightening it firmly provides a Good Enough™ grip:
Clamp the other end of the wire into the bench vise, pull gently on the hammer to take the slack out of the wire, and slap the weight until one end of the wire breaks.
With a bit of attention to detail, the wires come out perfectly straight and ready to become Art:
The wires start out at 1.60 mm diameter (14 AWG should be 1.628, but you know how this stuff goes) and break around 1.55 mm. In principle, when the diameter drops 3%, the area will decrease by 6% and the length should increase by 6%, but in reality the 150 mm length stretches by only 1 mm = 1%, not 3 mm. My measurement-fu seems weak.
Highly recommended, particularly when your Favorite Wife made the tool.
The Harbor Freight version comes with a bunch of snouts suitable for car repair and is utterly unromantic.
Astable Multivibrator: Monochrome Pirhana LED
Posted by Ed in Electronics Workbench, Software on 2019-01-17
The LED parts box disgorged some single-color Pirhana-style LEDs:
Didn’t quite catch the blink, but the Ping-Pong ball radome lights up just as you’d expect.
The radome sits on a stripped-down RGB LED spider:
The circuitry is the same as the First Light version, with a 1 MΩ resistor stabilizing the LED ballast resistor:
Those are 1 µF ceramic caps in the astable section, so I’m no longer abusing electrolytics, and a stylin’ 100 nF film cap metering out the LED pulse up above.
Just for pretty, I’ve been using yellow / black wires for the battery connections and matching the LED color with its cathode lead.
The OpenSCAD source code as a GitHub Gist:
Minilathe MT3 Spindle Collet Fitting
Posted by Ed in Machine Shop, Oddities on 2019-01-16
I’ve used the LMS set of inch-size MT3 spindle collets on occasion, but releasing them required an unseemly amount of drawbar battering. It recently occurred to me to check their fit in the spindle taper:
Minilathe – MT3 collet – taper test
Huh.
The only place they touch the spindle is right around the base, so it’s no wonder they clamp poorly and release grudgingly. I tried several others with the same result.
Cross-checking shows a much closer fit along the entire length of the dead center, so it’s not the spindle’s fault:
Minilathe – Dead Center – MT3 taper check
Stipulated: we’re not talking toolroom precision here
I set the collets on centers:
Minilathe – MT3 collet – drive setup
And proceeded to file away the offending section to move the clamping force closer to the business end of the collet:
Minilathe – MT3 collet – filed result
I did the small collets, the ones I’m most likely to need, and left the big ones for another rainy day.
They don’t have much clamping range and seem good only for exact-inch-size rods.
I should lay in a stock of ER16 and maybe ER32 collets for small stuff.
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