Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The top surface of the Anker LC40 flashlight serving as the daytime running light on Mary’s bike sees plenty of sunlight, particularly when it’s sitting beside her garden plots, and the black anodized finish on the screw-in battery cap has begun fading:
Anker LC40 Flashlight – Anodizing fade
The bottom side of the cap is in fine shape, as is the main case, so the two parts came from different metal finishing lines.
The light on my bike, a marginally newer and essentially identical Bolder LC40, remains all black. I have no idea what “Bolder” means in this context.
The question occasionally comes up as to why one would want a Tektronix A6302 Hall effect current probe and AM503 amplifier. The answer is simple: non-contact, essentially non-invasive current monitoring.
The scope screen in the background shows the two base voltages at the top, plus the overall battery current along the bottom:
Tek A6302 – Astable multivibrator – LED current 1 mA-div
The current at 1 mA/div shows plenty of noise, but the 200 ms LED pulse is barely 1 mA tall. The two AA alkaline cells have faded to 2.5 V, so the “wearable” white-LED-with-dyed-overcoat runs far under its nominal 3.6-ish V spec.
There’s basically no other way to get that result, because inserting a current-sense resistor into the circuit will alter the results, plus be intractably difficult to measure, particularly if you need the current in a non-ground-referenced branch of the circuit.
The AM503 has terrible thermal drift, by contemporary standards, but after the first half-hour or so it’s manageable for short durations. I’m thinking of epoxying a small knob to the screwdriver-adjustable twiddlepot to simplify the baseline adjustment.
Alas, even non-working probes and amps have become eBay collectables. You could, of course, buy new.
Although the pair of Ortlieb Back-Roller packs on Mary’s bike make her look like a long-distance tourist, we’re actually on our way to her garden plot:
AS30V-0285
The left-side pack suddenly seemed unusually floppy:
AS30V-0300
One second later:
AS30V-0360
Another second and it’s visible under my right hand:
AS30V-0420
The view from her bike at about the same time:
Ortlieb-0158
I’m expecting to fall to my right, but it’d have been better if I hadn’t kicked the bag:
Ortlieb-0169
The pack went under the rear wheel and out the far side:
Ortlieb-0185
Where it came to rest in the middle of the trail:
Ortlib pack drop – aftermath
Elapsed time from the first picture: just under 5 s.
Did you notice the other cyclist in the other pictures? She’s why I veered so hard to my right!
A pair of these latches hold the pack onto the rear rack:
Ortlieb pack drop – QL latch detail
When they’re properly engaged, they look like this:
Ortlieb pack drop – QL latch – secure
When they’re not, they look like this:
Ortlieb pack drop – QL latch – whoopsie
Which is obvious in the picture and inconspicuous in real life.
The strap emerging from the top of the latch serves as both a carrying handle and latch release: pull upward to open the latches and release them from the bar, lift to remove the pack, and carry it away as you go. Installing the pack proceeds in reverse: lower the pack onto the rack bar, release the handle, and the latches engage.
Unless the pack is empty enough to not quite fully open the latches as you carry it, in which case the closed latches simply rest on the bar. We’ve both made that mistake and I generally give her packs a quick glance to ensure sure they’re latched. In this case, the plastic drawer atop the racks (carrying seedling pots on their way to the garden) completely concealed the pack latches.
Tree roots have been creasing the asphalt along that section of the rail trail: the bike finally bounced hard enough to lift the drawer and fall off the rack rod.
Memo to Self: In addition to the visual check, lift the packs using the strap across the middle holding the rolled-down top in place. Remember, don’t check by lifting the carrying handle, because it just releases the latches; another easy mistake to make.
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.
The ESP8266 controller in Sophi’s blimp project suffered from random resets, which I was absolutely certain happened when the current for the three DC prop motors glitched the battery supply. So I hauled the Tek current probes + amps + scope to a Squidwrench meeting and, after considerable fiddling, we found a smoking … trace:
Regulator dropout
The purple trace shows the Li-Ion battery voltage at an inactive motor driver located on the far end of a known-to-be-too-small trace. In principle, there’s little-to-no current drawn through that trace, so it should represent the voltage at the regulator input.
The green trace shows the 3.3 V regulator output at its bulk storage cap.
The ground reference is at the PCB’s battery negative connection pad.
The bold dotted green cursor shows the regulator output hitting 2.57 V, entirely low enough to glitch the ESP. The scope triggers on negative-going edges below 2.6 V and this was the first trigger after starting and running the motors for a few seconds.
Conspicuous by its absence: any hint of a current glitch in the yellow trace from a Tek A6302 probe clamped around the battery positive wire. The current remains constant at the 400 mA (100 mA/div) level drawn by two DC motors, with no sign of any glitches whatsoever; she’s not using PWM speed control. The whole board draws about 80 mA DC and the ESP’s WiFi radio pulls 200 mA pulses, so all’s quiet on those fronts.
Which is why I like to measure actual circuit operation: I vastly prefer to solve actual problems, knowing what does (or doesn’t!) cause them helps, and I’m not at all bothered by being wrong.
The regulator output doesn’t go much above 3.3 V, which is comforting.
However, when the regulator’s input voltage falls below 3.3-ish V, its output voltage tracks right along down with it. Input variations above 3.3-ish V don’t make much difference in the output.
Although it’s a buck-boost converter, its response time isn’t fast enough to cope with something else on the PCB pulling enough current to spike its input voltage (shared with the motor driver) below 3.3 V. The dropout is barely 4 ns long, far shorter than the regulator’s switching period.
I have my doubts as to the accuracy of those voltage waveforms and, in particular, their pulse widths. IIRC, the scope can trigger on a pulse exceeding a specific width, but I’d devote more time arranging the test points and getting RF-quality connections / grounding before going further out on a numeric limb.
This single trigger event may not be the glitch causing the reset. What it does show is the regulator output dropping below the ESP’s absolute-minimum input voltage spec, at least briefly, which is cause for concern.
This is just after noon, when deer should be snoozing, north of Paula’s Public House, with the deer on the creek side of the road. I’m towing the trailer with an empty propane tank, coasting down from 18 mph, and expecting the deer to jump in front of me, because that’s what deer do. It waited patiently until I passed, hopped the guide rail, trotted across the road, then clambered up the steep hillside away from the Mighty Wappinger Creek.
Searching for deer will reveal many more encounters.
We heard God’s Own Weedwhacker off to the right as we approached Jackson Drive on the way home:
Chopper over power lines – Vassar Rd near Jackson Dr – 2018-06-11
The chopper followed the power lines, just over the treetops, with the downdraft thrashing the leaves:
Chopper over power lines – Vassar Rd near Jackson Dr – rear camera – 2018-06-11
Long ago, I attended a talk about using choppers for power line inspection and maintenance. Apparently, someone with nerves of ice can replace insulator supports and aeolian dampers on high-tension lines while perched on a chopper hovering very very close to the conductors. Pilots with experience getting troops into and out of hot LZs are in high demand.
I’m sure they give the E911 call center a heads-up before taking off …
The Smell of Molten Projects in the Morning 