Archive for October, 2019
I picked up a pair of Raspberry Pi V1 cameras, both of which arrived unstuck to their breakout board:
Requiring the customer to peel off the white layer and stick the camera to the PCB helps keep costs low. They’re $4 if you’re willing to wait two months or $7 from a “USA Seller”.
Apparently, “porcelain chip fix” epoxy survives about a year in a bathroom sink:
It came loose from the drain rim while I was cleaning the sink; I wasn’t doing anything particularly vigorous.
The stain in the lower right goes all the way around the epoxy:
For what should be obvious reasons, I was loathe to scuff up the sink surface to give the epoxy a better grip, so it couldn’t make a watertight seal all the way around.
A closer look at the stain:
I’m reasonably sure that’s iron bacteria colony, rather than actual rust, as there’s no iron to be found anywhere nearby.
For lack of anything smarter, I’ll apply another dose of the same epoxy, although this time I won’t be expecting a long-term fix.
The fixtures are centered at X±70.0 mm / Y=0.0 from the G54 workspace coordinate origin dead-center in the middle of the platform, with G55 centered on the HD fixture to the left and G56 on the CD fixture to the right.
So the engraving workflow amounts to homing the CNC 3018 when I turn it on, taping a platter in a fixture, selecting the corresponding WCS, loading a suitable G-Code file, and firing it off. It seems bCNC returns to G54 after completing the file, so verifying the WCS selection every time is Very Good Practice.
The friable lacquer coating on some CDs fills my world with glitter whenever I engrave a pattern on their label side. I didn’t plan on a dust shoe for this thing!
Looking into the end, you can see where the next segment would attach:
Somewhere nearby, there’s a recently vacated nest with a pantry full of carefully chosen seeds and nuts, just waiting for another critter to move in …
Voles apparently live only a few months, so this one may have run out of gas while crossing the driveway:
Or it just caught a heart attack?
It definitely wasn’t playing possum; nobody can lie still with ants up their nose.
It had vanished when we returned from our afternoon ride, so somebody further up the food chain also noticed it. As my buddy dBm puts it, “In Nature, nothing goes to waste.”
Which snapped together exactly like it should:
A strip of double-sided foam tape attaches it to the Pi’s case, which is Velcro-ed to the M2’s frame. The cable may be too long, but avoids sharp bends on the way out of the case.
The whole lashup works fine:
That’s a second set intended for the CNC 3018-Pro, but it didn’t fit quite as well. The B brackets are slightly too long (or their pivots are slightly too close to their base) to allow the C plates to turn 90° to the mount:
Nothing one can’t fix with nibbling & filing, but I long for parametric designs …
I got an Alead / Nolan HearLinks (many adjectives) Telecoil receiver to boost my ability to hear music & presentations at Vassar, because they recently slotted telecoil loops into the floors of their public venues. It took a few concerts to get the appropriate volume setting, after which I wondered how sensitive the receiver was:
The small T in the upper right corner marks the receiving coil location, with the coil oriented parallel to the body’s long axis. It’s the secondary winding of an air-core transformer with a single-turn (perhaps using Litz wire) primary embedded in the floor, with the induced voltage obeying the usual transformer equation:
V = 2π µ₀ µr N A f H cos θ
- µ₀ – vacuum permeability = 4π×10-7 H/m
- µr – relative permeability
- N – number of turns
- A – receiver loop area, m²
- f – signal frequency, Hz
- H – magnetomotive force, A/m
- θ – angle between windings
For a given installation and receiver position, pretty much everything is fixed, with the voltage depending only on the H field caused by the primary winding current.
The induced voltage is linearly dependent on the frequency, but the transmitter equalization filters apparently flatten the spectrum to get equal receiver amplitude between about 100 Hz and 5 kHz.
The coil in that picture has nine turns, with four passing through the Tek current probe. Applying 10 mVpp to the winding produces a corresponding current:
The scope sees 14 mVpp = 1.4 div at 1 mA/div = 1.4 mA. Dividing by 4 turns means the coil actually carryes 350 µA. The signal generator has a 50 Ω output impedance, so 10 mV should produce about 200 µA, which seems a bit low. On the other paw, the signal generator sees the coil as a dead short at 1 kHz, so I don’t trust the numbers.
Whatever magnetic flux it may be produces a 1 kHz tone at a somewhat higher volume (for the same receiver setting) than the fancy Vassar loops, so the flux is in the right ballpark. With a bit more attention to detail, perhaps I can tinker up a current-mode loop drive amplifier.
The Alead receiver has an internally generated tick audible at the audio volume I need for the Vassar loops, which is 5 to 7 steps down from the maximum volume at 15 steps. It seems related to the internal Bluetooth hardware, although it’s present even when the receiver is not paired with my Pixel phone and, in fact, is unchanged even when 100 feet from the nearest electronic device.
When I reported the problem, they said:
Yes, you can hear very minor tick sound on telecoil mode. It is caused by some electronic and current to make those tick sound. Sorry for this defective on the design.
It had one job that it doesn’t do well, so it’s on the way back for a refund.
Evidently, I must build an audio loop receiver to get what I want …