Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Category: Science
If you measure something often enough, it becomes science
Not much to my surprise, my hack-job thermistor rebuild went bad:
M2 – thermistor – assembly 2
Having nothing to lose, I heated the brass tube over a butane flame to wreck the epoxy, which blew out with a satisfactory bang and filled the Basement Laboratory with The Big Stink.
Much to my surprise, the active ingredient still worked:
M2 DIY thermistor corpse
The multimeter reported absolutely no intermittent dropouts for as long as I was willing to watch the trace while doing other things:
DIY Thermistor Autopsy – Resistance Trend
So it must be my crappy soldering technique.
A brace of real M2 thermistors will arrive shortly …
We’re waiting at the end of Burnett Blvd, with the signal red and the clock at T = -0.17 seconds (photo numbers in 1/60 second frames):
RedRunner-0194
You can’t hear the car (barely visible) approaching on the far left, but we can.
T = 0.00 – We get a green light and the (more visible) car is accelerating hard:
RedRunner-0204
T = 1.00 – The car reaches the crosswalk:
RedRunner-0264
Note that the driver of the car to our right isn’t moving, either.
T = 2.03 – Car passes through intersection:
RedRunner-0326
The view from above, showing the distance between those two positions is 100 feet:
Burnett at Rt 55 – Distance along Rt 55
Do the math: 100 ft / 1.03 s = 97 ft/s = 66 mph.
There’s a reason we don’t start moving instantly when a traffic signal turns green.
T = 3.17 – We start moving, as does the car to our right, with our signal still green:
RedRunner-0394
T = 4.88 – Whoops, our signal turns yellow:
RedRunner-0497
T = 9.28 – Our signal turns red:
RedRunner-0761
The signal timing hasn’t changed over the years:
Green = 4.88 s
Yellow = 4.40 s
Elapsed time from green to red: 9.28 seconds. No problem if you’re a car, death if you’re a bike.
T = 10.42 – We’re pedaling hard in the intersection:
RedRunner-0829
The white car to our far right started moving into the intersection about the time we did. If you’re going to say we shouldn’t run the light, you gotta deal with cars first, OK?
Note the car approaching from the right on the far side of Rt 55. That’s a 40 mph zone, the driver sees a green light, and we’re still in the intersection.
T = 12.50 – We’ve been moving for 9.33 s, which puts Mary directly in the path of the oncoming car:
RedRunner-0954
T = 14.83 – The oncoming driver having spotted us and slowed down, we’re asymptotically approaching the right-hand lane of Rt 55, passing beyond the steel manhole cover:
RedRunner-1067
If you plunk “burnett signal” into the search box at the upper right, you’ll find plenty of previous incidents along these lines.
Despite bringing this hazard to their attention many times (“We appreciate and share your interest in making our highway systems safe and functional for all users.“), NYS DOT obviously doesn’t care.
If any of their employees commuted to their office building (which overlooks this very intersection), perhaps they would care, but they don’t: we have yet to see a bicycle in the DOT’s token bike rack.
DOT says they’re in favor of Complete Streets, but, seven years on, it’s just another day on the only route between Arlington and the Overocker Trailhead of the Dutchess County Rail Trail.
For future reference, the rebuilt wheel spoke tensions came out around 25, slightly lower than the 27-ish I measured on Mary’s bike; it didn’t occur to me to measure the tension until after I’d relaxed the spokes. I’ll ride it for a while before doing any tweakage.
The spoke pattern is pretty close to four-cross, due to the large-flange Phil Wood hubs:
Tour Easy Front Spoke Pattern
Which makes for a hella-strong wheel, particularly seeing as how it’s very lightly loaded. The Tour Easy we got for our lass came with a radially spoked rim around a Phil hub.
I transferred the hub and laced spokes intact to the new rim by the simple expedient of duct-taping the spokes into platters, removing the nipples, stacking the rims, sliding the spokes across into their new homes, reinstalling the nipples, then tightening as usual.
We’ve been using it daily ever since and it spends most of its life drip-drying in the dish drainer. I added a third opening to the cheerful orange measuring spoon holder just for the slicer.
A few weeks ago I noticed corrosion once again growing on the handle:
Cheese Slicer – epoxy coat – corrosion – detail
I think the rot comes from water diffusing through the epoxy, rather than gross leaks through damage or pinholes. The tip of the handle has the most corrosion, probably due to the water drop hanging there, even though it also has the thickest epoxy coating: it cured with the handle pointing downward.
Apparently folks have been going around the curve in front of the Dutchess County BOCES site at a pretty good clip. I didn’t spot any scars in the grass off the high side, but ya never know.
We’re at the top of an uphill section and, riding together, we’re not sprinting for town line signs.
Ex post facto notes from the third Squidwrench Electronics Workshop.
Exhibit various 50 Ω resistors, including my all-time favorite, a 600 W 3 GHz dummy load:
600 W Dummy Load Resistor
… down to a 1/8 Ω metal film resistor.
The dummy load’s N connector triggered a regrettable digression into RF, belatedly squelched because I wasn’t prepared to extemporize on AC concepts like reactance which we haven’t covered yet.
Discussion of resistor applications, power handling, power derating with temperature, etc:
Whiteboard – Session 3 – Resistor power derating
Why you generally won’t find 50 Ω load resistors in Raspberry Pi circuits. Cartridge heaters for 3D printers, not aluminum power resistors, although everyone agrees they look great:
Power resistors on heat spreader
Discussion of voltage vs. current sources, why voltage sources want low internal resistances and current sources want high resistances. Bungled discussion of current sources by putting diodes in parallel; they should go in series to show how added voltage doesn’t change current (much!) in sources driven from higher voltages through higher resistances:
Whiteboard – Session 3 – Voltage vs Current Sources
Use Siglent SDM3045X DMM in diode test mode to measure forward drop of power / signal / colored LEDs, discuss voltage variation with color / photon energy. Measure 1.000 mA test current for all forward voltages.
Compute series resistor (500 Ω) to convert adjustable power supply (the digital tattoo box, a lesson in itself) into reasonable current source; roughly 10 V → 20 mA. Find suitable resistor (560 Ω) in SqWr junk box parts assortment, digression into color band reading.
Wire circuit with meters to measure diode current (series!) and voltage (parallel!), measure same hulking power diode (after discovering insulating washers now in full effect) as before in 1 mA steps to 10 mA, then 15 and 20 mA, tabulate & plot results:
Whiteboard – Session 3 – Diode current vs forward drop
Discover warm resistor, compute power at 20 mA, introduce cautionary tales.
Lesson learned about never returning parts to inventory, with 560 Ω resistor appearing in diode drawer. Cautionary tales about having benchtop can of used parts as front-end cache for inventory backing store.
The Smell of Molten Projects in the Morning 