Archive for category Science
Given that I no longer trust any of the knockoff Neopixels, I wired the remaining PCB panel into a single hellish test fixture:
The 22 AWG wires deliver +5 V and Common, with good old-school Wire-Wrap wire passing to the four LEDs betweem them. The data daisy chain snakes through the entire array.
It seems only fitting to use a knockoff Arduino Nano as the controller:
The code descends from an early version of the vacuum tube lights, gutted of all the randomizing and fancy features. It updates the LEDs every 20 ms and, with only 100 points per cycle, the colors tick along fast enough reassure you (well, me) that the thing is doing something: the pattern takes about 20 seconds from one end of the string to the other.
At full throttle the whole array draws 1.68 A = 60 mA × 28 with all LEDs at full white, which happens only during the initial lamp test and browns out the supply (literally: the blue LEDs fade out first and produce an amber glow). The cheap 5 V 500 mA power supply definitely can’t power the entire array at full brightness.
The power supply current waveform looks fairly choppy, with peaks at the 400 Hz PWM frequency:
With the Tek current probe set at 200 mA/div, the upper trace shows 290 mA RMS. That’s at MaxPWM = 127, which reduces the average current but doesn’t affect the peaks. At full brightness the average current should be around 600 mA, a tad more than the supply can provide, but maybe it’ll survive; the bottom trace shows a nice average, but the minimum hits 4.6 V during peak current.
Assuming that perversity will be conserved as usual, none of the LEDs will fail for as long as I’m willing to let them cook.
The Arduino source code as a GitHub Gist:
The other side shows where the ink stopped seeping under the silicone:
I don’t know if I melted the side of the LED or if it came that way, but, oddly, there’s no leakage on that side.
This LED matches the layout of Josh’s “crappy” LEDs, as does the entire lot below, although I suspect that’s more coincidence than anything else; there aren’t that many different layouts around.
Flushed with success, so to speak, I ran the Sharpie around all the unused LEDs from that order:
I tested the process on the three LEDs in front, then wiped the ink off with denatured alcohol.
A closer look shows the ink all around the silicone-to-case border, with plenty of opportunity to seep in:
After wiping the ink off, none of the 31 unused LEDs showed any sign of poor sealing.
I haven’t been keeping good records of the failures, but right now I have twelve functional WS2812 LEDs attached to various glass doodads. That leaves 7-ish failed LEDs out of the 15-ish with long term use (not counting four recent replacements).
In round numbers, that’s a 50% failure rate…
I should wire up the remaining sheet of LEDs as a test fixture, let them cook for a while, and see what happens.
A turkey flock forages through the bottomlands along the Wappinger Creek and, at night, roosts in the trees at the far end of our driveway:
I’m a sucker for that moon:
It’s rising into the eastward-bound cloud cover bringing a light snowfall, so we missed the penumbral eclipse.
If you’re counting turkeys, it’s easier with a contrasty IR image:
Mary recently counted forty turkeys on the ground, so that’s just part of their flock. I think their air boss assigns one turkey per branch for safety; they weigh upwards of 10 pounds each!
Taken with the DSC-H5 and DSC-F717, both the the 1.7× teleadapter, hand-held in cold weather.
Further results from the SDR-based WWVB receiver:
Seven hours of mid-January RF, tight-zoomed in both frequency and amplitude, from 0350 to 1050 local:
The yellow line of the WWVB carrier comes out 2 ppm high, which means the local oscillator chain is 2 ppm low. We know the WWVB transmitter frequency is exactly 60.000 kHz, translated up by 125 MHz to the N3’s tuning range; you can, ahem, set your clock by it.
The blue band marks the loop antenna + preamp passaband, which isn’t quite centered around 60.000 kHz. Tweaking the mica compression caps just a bit tighter should remedy that situation.
Given that input, a very very tight bandpass filter should isolate the WWVB carrier and then it’s all a matter of fine tuning…
The 2016-11A and 2016-11B cells produced the overlapping red and green curves, with the gritty section due to crappy battery pack connections:
The lower curve comes from an old unprotected cell harvested from a defunct media player and retrieved from the to-be-recycled pile.
I picked 1 A as a reasonable value for their intended use in flashlights and maybe a helmet camera. Unlike some other cells in the recent past, these deliver 3.0 A·h, reasonably close to their rated 3.4 A·h capacity at a (presumably) lower current.
Replotting the voltage vs. energy delivered doesn’t show any surprises:
The voltage declines more-or-less linearly, without the relatively flat discharge curve for smaller cells, which explains why the J5 V2 flashlight becomes seriously dim after a few hours. On the upside, that allows a reasonably accurate state-of-charge display.
Assuming the Sony HDR-AS30V camera burns 0.1 W·h/min while recording (which is a fancy way of saying it dissipates 6 W), then it should run for (10 W·h)/(0.1W·h/min) = 100 min from one of these cells fitted as an outrigger. The best of the NP-BX1 cells for the camera delivers something like 90 minutes from a measured capacity of 4 A·h at 500 mA; I don’t know what to make of those numbers. Perhaps the camera runs the NP-BX1 cells below the 2.8 V cutoff I’ve been assuming?
Page views for 2016:
That works out to a bit under 1000 page views/day of purely organic traffic.
As always, way more people than I’d expect come here with plumbing problems. On the upside, much of the bedbug saga has fallen off the trailing edge of the wedge; life is good!
The Hobo datalogger buried in the dirt under the patio kvetched about a low battery, which produced this surprising result: