The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Author: Ed

QRPme Pocket Pal II: RF Waveforms and Meter Test

The QRPme Pocket Pal II produces RF test signals in the 20 meter and 40 meter bands, both square-ish waves derived from its 14.31818 MHz oscillator-in-a-can:

QRPme 20 meter – clip leads

That’s the 20 meter signal, seen through the twisted pair test lead with alligator clips clamped on the scope probe, thusly:

QRPme Pocket Pal II – clip leads to probe tip

When you’re working with RF signals, the “ground” part of the probe circuit matters:

QRPme 20 meter – probe tip gnd

That’s with the probe and its short spring ground jammed directly into the header:

QRPme Pocket Pal II – probe tip gnd

Well, in this case, signal quality doesn’t matter very much, as you’re using the Pocket Pal II at a hamfest (or your bench) to determine if an HF radio is completely dead.

Here’s the 40 meter output, with the J3 jumper in place and the probe jammed into the header:

QRPme 40 meter – J3 on – probe tip gnd

Pulling the J3 jumper off doubles the test signal amplitude:

QRPme 40 meter – J3 off – probe tip gnd

Nothing wrong with those signals! In a pinch, those edges probably produce harmonics up in the UHF bands.

For completeness, here’s the 250 μA DC output driving a contestant chosen from the Box o’ Meters:

QRPme Pocket Pal II – 250 uA meter test

Eyeballometrically, the meter wants to see 1 mA for full-scale deflection, which is the whole point of the tester.

Recommended, with some early notes.

2018-06-06
Rt 376 Overgrowth: Red Oaks Mill to Maloney Rd

The weeds are once again taking over the shoulder along Rt 376 south of Red Oaks Mill:

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New shoots from the Japanese Knotweed stand just north of Maloney Rd have begun punching through the asphalt along the edge of the shoulder.

This section is in the purview of NYS DOT’s Dutchess South Residency, extending south of Red Oaks Mill to the end of Rt 376 near Hopewell. In contrast, DOT’s Dutchess North Residency continues to keep Rt 376 well-trimmed northward from Red Oaks Mill to Poughkeepsie. I’ve never gotten any explanation why the two Residencies have such strikingly different weed-control standards.

2018-06-05
FM DDS: First Light Hardware

Some Barely Viable Prototype hardware for a frequency modulated DDS to replace Channel Elements requiring now-unobtainable crystals:

FM DDS – First Light layout

The heatsink (surely harvested from a PC, then salvaged from a box o’ goodies) runs about 25 °C above ambient while dropping a 12 V input to 5 V at 180 mA, so it’s good for maybe 2°C/W. It carries a KA278RA05C LDO regulator; you’d probably want something fancier in real life.

The AD9851 DDS requires a 5 V supply to run at 180 MHz from the 30 MHz oscillator on its PCB, with the side effect of putting its minimum Logic 1 Voltage threshold at 3.5 V. Because the Teensy 3.6 runs at 3.3 V from its own on-board linear regulator, the DIP 74AHCT125 level shifter between the two boosts the Teensy’s LVCMOS SPI signals to good old TTL.

The sticker on the CPU reminds me of the jumper cut between the USB +5 V line and the VIN pin, thus putting the Teensy on the better-regulated local supply for the benefit of its ADC reference:

Teensy 3.6 Back – VIN to VUSB jumper

The picture comes from PJRC’s exceedingly helpful Teensy 3.6 reference cards.

I ran header pins along both sides of the Teensy to simplify attaching scope probes and suchlike; the dangling gray wire brings the scope’s Arbitrary Function generator signal to the Teensy’s A9 input.

The FMDDS Mock 3 firmware lit right up, albeit with the faceplant of sending the SPI bytes in the wrong order and the wrong bit direction, which was easily fixed after a bit of puzzling:

FM DDS 10 MHz – SPI 16 MHz LSB

Just a typo, could happen to anyone …

2018-06-04
Tour Easy: Front Derailleur Cable Angle

Spotted while in the midst of replacing my Tour Easy’s rear grip shifter:

Tour Easy – front derailleur cable angle

As you might expect, the cable saws through the side of its ferrule and the brazed-on frame fitting, because it’s been basically impossible (for me, anyhow) to find a replacement derailleur duplicating whatever the good folks at Easy Racers shipped back in 2001.

On the upside, this derailleur’s cable entry has a nicely rounded ramp eliminating the need for my brass cable pulley widget.

Memo to Self: Perhaps running the cable around a bearing anchored to the frame fitting would help?

I’ve obviously forgotten to fix this for several years, so putting it here may serve as a Round Tuit.

2018-06-03
Tiny Turtle Teleportation: Rail Trail

This little critter was chugging across the Dutchess Rail Trail near the ponds north of Page Industrial Park, so I stopped to lend a hand:

Tiny Turtle Dorsal – Rail Trail – 2018-05-23

The plastron looked like a brightly colored jewel:

Tiny Turtle Ventral – Rail Trail – 2018-05-23

Perhaps plastrons start out with all the pigment they’ll ever have, then fade from bright orange to yellow-brown as they spread out.

If you’re not paying attention, you’d think “pebble” or “dog turd”. Neither of which you should ride over, of course, but … teleporting a tiny turtle to the drainage ditch on the far side seemed to increase the world’s net happiness.

The pix are tight crops from the AS30V’s 170° FOV images, which means they’re way grittier than you’d expect from a “full HD” image.

2018-06-02
Monthly Science: Water Bottle Refill Stations

The O’Neill Center at WCSU has two sets of drinking fountains:

Water bottle refill stations

The bottle shape on the back of each fountain marks the sensor for its water bottle refill spout. The small rectangular block above and right of the sensor is a virtue signalling display giving the number of disposable bottles allegedly not consigned to a landfill.

The left fountain:

Water bottle refill station – left

The center fountain:

Water bottle refill station – center

The right fountain:

Water bottle refill station – right

Which looked exactly like either a test pattern or a failed display, until I waved my hand over the senor and watched it increment to 00008889. Timing is everything!

The other trio of fountains had the same progression, so it must be a chirality thing.

I can’t say whether you should use the left fountain to avoid some germs or the right fountain for the freshest water. Not having to maneuver our bottle under the usual arch from a drinking nozzle was a big win, though, so mad props to ’em.

2018-06-01
Primo Comet vs. Green Glass Chip: Kevlar FTW!

The gashes don’t look like much:

Primo Comet gash – tread view

Not even from the side:

Primo Comet gash – side view

When they happened, I knew where to look, because the Kevlar-belted Primo Comet had two conspicuous bulges surrounding debris jammed between the tread and the carcass along the sidewall: the gashes were wide open!

Much to my astonishment, the tire hadn’t gone instantly flat.

Some screwdriver probing in the leftmost gash produced this nasty glass chip:

Primo Comet gash – chip side view

AFAICT, the smooth side slid over the internal Kevlar belt as the edge sliced between the rubber tread and the carcass. I think the top entered first, with the somewhat crushed end hitting the pavement on each revolution:

Primo Comet gash – chip edge view

The other gash emitted a somewhat smaller chip.

I rode over something crunchy, most likely the remains of a beer bottle, in a shaded section along Rt 376, and we stopped a few driveways later to diagnose a once-per-revolution thump from the front tire. The tube still wasn’t losing pressure, even after extracting the glass, so I continued the mission; it was a fine day for a ride!

I later filled those gashes (plus a few others) with silicone rubber to keep grit out. It’s surely a feel-good gesture, but maybe it’ll help the tire reach the end of its tread life.

You can judge our “riding environment” by the tire’s condition …

2018-05-31