Archive for December, 2018
Six Gallon Can Lid Adapter to Platform Bird Feeder
Posted by Ed in Home Ec, Machine Shop, Science, Software on 2018-12-11
A House Finch suffering from Finch Eye Disease prompted me to sterilize our feeder, which meant providing a temporary feeder to keep the birds flying. Having an abundance of lids from six gallon plastic cans / buckets, this made sense:
Can Lid Feeder – installed
Which required an adapter betwixt pole and lid:
Can Lid Feeder – assembled
Which requires a bit of solid modeling:
Can Lid Platform Feeder Mount – solid model – bottom
The lids have a central boss, presumably for stiffening, so the model includes a suitable recess:
Can Lid Platform Feeder Mount – solid model – support structure
As usual, automatically generated support fills the entire recess, so I designed a minimal support structure into the model and cracked it out with very little effort:
Can Lid Feeder – support structure
The tangle off to the right comes from a bridge layer with a hole in the middle, which never works well even with support:
Can Lid Platform Feeder Mount – Slic3r – bridge layer
Didn’t bother the birds in the least, though, so it’s all good.
I loves me my 3D printer …
The OpenSCAD source code as a GitHub Gist:
Dutchess Rail Trail: Maloney Rd Trailhead Ruts
Posted by Ed in Oddities, Recumbent Bicycling on 2018-12-10
It seems the DCW&WA SUV makes regular trips through the “No Motor Vehicles” bike access:
Maloney Rd Trailhead – 2018-11-07
If it’s not them, then it’s somebody following their example.
Just because you can do something, doesn’t mean you should … but, of course, the ordinary rules apply only to little people, not public servants.
Someone in the bike advocacy apparat once told me I’m the most cynical, bitter person they’d ever met, at least on the subject of getting along with public servants. As I see it, I came by my attitude honestly.
Sterling Table Knife Repair
Posted by Ed in Home Ec, Machine Shop on 2018-12-09
A sterling knife followed me home after a Thanksgiving gathering:
Sterling knife repair – powdered cement
The original cement, dating back to the middle of the last century, turned into friable dust around the blade tang:
Sterling knife repair – handle socket
I cleaned it out as best I could, buttered JB Quik epoxy around the tang and into the socket, joined the two, and let it cure in the natural position:
Sterling knife repair – curing
The rest of the knives in the set may need similar attention, but I’m not looking for trouble.
Three Dead Mice
The rodents around here have great trouble with outdoor bowls, but this trio ended in a deep six gallon bucket next to the garage workbench:
Three Dead Mice
Even though mice don’t seem like cuddly creatures, they ended their days snuggled together; we’ll just ignore the cannibalism thing.
Heck of a way to go, even for rodents. I renewed the steel wool blocking a gap in the garage door.
Halogen Desk Lamp Conversion
Posted by Ed in Electronics Workbench, Home Ec, Machine Shop on 2018-12-07
As part of converting the halogen desk lamp to LEDs, I replaced the hulking iron transformer with a flatter counterweight:
Halogen Desk Lamp – 12 V 20 W transformer
Under normal circumstances, you’d use something like steel or lead sheets, but Tiny Bandsaw™ can’t cut any appreciable thickness of steel and I gave away my entire lead stockpile, so I sawed disks from a pile of non-stick pancake griddles and drilled suitable mounting holes:
Parallel clamps in action
Another disk (from a formal aluminum sheet!) goes into the lamp head, with a trio of 3W COB LEDs epoxied in place:
Ex-Halogen Desk Lamp – 3x3W COB LED assembly
The other side of the disk sports a heatsink harvested from a PC, also epoxied in place:
Ex-halogen Desk Lamp – heatsink fitting
Realizing the head required only a little filing to accommodate the heatsink sealed both their fates.
A test firing showed the heatsink needed more airflow, which didn’t come as much of a surprise, so I milled slots in the lamp head:
Ex-halogen Desk Lamp – vent slot milling
Deburring the holes, blackening the sides with a Sharpie, and tucking a bit of black window screen behind the opening made the vents look entirely professional.
The small dome in the base originally cleared the transformer and now holds the entire 10 W LED driver, along with all the wiring, atop the counterweight sheets:
Ex-halogen Desk Lamp – base wiring
A cork pad covers the base for a bit of non-skid action:
Ex-halogen Desk Lamp – cork pad
I couldn’t convince myself filling in those sectors would improve anything, so I didn’t.
And then It Just Worked:
Ex-halogen Desk Lamp – in use
All without a trace of solid modeling or G-Code …
JYE Tech DSO150 Oscilloscope vs. Actual Signals
Posted by Ed in Amateur Radio, Electronics Workbench, Science on 2018-12-06
The DSO150 oscilloscope’s specs give a 200 kHz bandwidth, so a 50 kHz sine wave looks pretty good:
DSO150 – sine wave 50 kHz 10 us-div
A 100 kHz sine wave looks chunky, with maybe 25 samples per cycle:
DSO150 – sine wave 100 kHz 10 us-div
The DSO150 tops out at 10 µs/div, so you can’t expand the waveform more than you see; 25 samples in 10 µs seems to be 2.5 Msample/s, exceeding the nominal 1 Msample/s spec. I have no explanation.
A 10 kHz square wave shows a blip just before each transition that isn’t on the actual signal:
DSO150 – square wave 10 kHz 20 us-div
At 50 kHz, there’s not much square left in the wave:
DSO150 – square wave 50 kHz 10 us-div
And, just for completeness, a 200 kHz square wave completely loses its starch:
DSO150 – square wave 200 kHz 10 us-div
A 10% (-ish) duty cycle pulse at 25 kHz has frequency components well beyond the scope’s limits, so it’s more of a blip than a pulse:
DSO150 – pulse 25 kHz 10 us-div
The pulse repetition frequency beats with the scope sampling and sweep speeds to produce weird effects:
DSO150 – pulse 25 kHz 100 us-div
Tuning the pulse frequency for maximum weirdness:
DSO150 – pulse 15 kHz 200 us-div
None of this is unique to the DSO150, of course, as all digital scopes (heck, all sampled-data systems) have the same issues. The DSO150’s slow sampling rate just makes them more obvious at lower frequencies.
Key takeaway: use the DSO150 for analog signals in the audio range, up through maybe 50 kHz, and it’ll produce reasonable results.
Using it for digital signals, even at audio frequencies, isn’t appropriate, because the DSO150’s low bandwidth will produce baffling displays.
JYE Tech DSO150 Oscilloscope: Battery Power
Posted by Ed in Electronics Workbench, Machine Shop on 2018-12-05
With the DSO150 scope running, I printed Geoff’s DSO150 case + battery holder from Thingiverse, added a few bits & pieces from the heap, and came up with a completely portable scope:
DSO150 battery hack – first light
The only scope mod consists of embedding a JST-ish connector in the back panel:
DSO150 battery hack – rear panel connector
Then soldering it to the battery pads and applying generous hot-melt glue blobs:
DSO150 battery hack – PCB power
Add a scrap 18650 Li-Ion cell, a regulated boost converter, and a switch:
DSO150 battery hack – interior
The switch is directly below the DSO150 BNC connector to get a little protection for its handle, which would otherwise stick out in harm’s way. This being an afterthought, I drilled the switch hole, rather than modify the solid model.
Some testing with a bench supply showed that the DSO150 will not operate correctly from the voltages produced by a pair of lithium cells, despite what you’d think from looking at the case. Below 8 V, the internally generated negative supply becomes larger than the positive supply, so the 0 V point isn’t properly centered and the scope loses headroom for large signals; monitoring the internal 3.3 V test signal makes the problem painfully obvious.
More color commentary from my summary email:
- Combining a case from Thingiverse with a Li-Ion cell and a regulated boost converter produces a portable scope.
- The PCB has provision for battery input, so I drilled / filed a square hole for a teeny JST-ish connector on the back panel, secured it with a blob of hot melt glue, and globbed the wires onto the PCB battery pads.
- The boost converter draws about 400 mA from the cell, so a 2500-ish mA·h cell should last Long Enough™. This is a scrap cell from the recycle box and gave out after maybe four hours.
- It idles at 8 mA, so I drilled a hole in the back of the case for a toggle switch disconnecting the battery; you’d want the hole in the solid model. Perhaps a better converter would have lower idle current; you’d never be able to tell from the eBay descriptions.
- Aaaaand it switches around 200 kHz under load, just barely beyond the scope bandwidth. It doesn’t add much noise to the signal, at least with a 50 Ω terminator jammed in the BNC, but the square-wave “cal” output looks awful at 50 mV/div; a real scope shows even more noise. I assume the noise comes directly from the logic supply; with luck, the DSO150’s analog circuitry has Good Enough™ filtering.
- Which might not matter for logic-level and moderate analog signals, of course, which is the whole point of the DSO150.
- Conspicuous by their absence: a Li-Ion cell protection PCB and any way to recharge the poor thing …
I’ve occasionally wanted a portable scope and now I have one!
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