Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Tag: Improvements
Making the world a better place, one piece at a time
The top pair of screw heads aren’t quite flush with the cover, so the knobs have 1 mm extensions:
Micromark Bandsaw – cover screw knobs – upper
The bottom pair sit inside 4 mm recesses, so those knobs get matching extensions:
Micromark Bandsaw – cover screw knobs – lower
Attacking an anonymous 5 mm hex wrench with a Dremel cutoff wheel produced a quartet of 12 mm shafts and reduced drawer clutter by one unit.
In retrospect, I should have dismantled the cover, grabbed the screws in a vise with their shafts vertical, and epoxied all the knobs with perfect alignment. Next time, maybe.
Having put the Tek AM503 with the 4 MHz oscillation (B075593) on the shelf pending arrival of what might be the world’s last remaining NOS 2625 op amp in the “screened and tested” 156-0317-03 grade, I figured I might as well go through the adjustment procedure on one of the bench units (B064098) to reset the gain and reduce the peaky leading edges (green trace):
Tek AM503 – B031510 B064098 – 10mA-div
I conjured a low-budget Special Adapter to feed signals into the front-panel connector:
Tektronix AM503 Special Adapter
I also used a somewhat smaller resistor in place of the required 3 Ω 3 W wire-wound unit:
Tek AM503 – 3 ohm test resistor
It need only soak up a few seconds of the degaussing signal and never even got warm, so it’s all good.
To my surprise, the square-wave output of the JDS6600 Function Generator meets the 10 ns risetime requirement:
JDS6600 Fn Gen – risetime 50 ohm
Perhaps half an hour of adapter shuffling and trimmer twiddling later, the AM503 output looked better:
Tek AM503 – compensation adj
The (purple) input comes from the function generator output through a BNC tee and an unterminated foot of coax, so the leading edge ringing is perfectly normal.
With the scope input now providing the 50 Ω termination and the Hall probe clamped around one wire of a clip-to-clip pair of BNC-to-alligator-clip adapters, we’re still not talking RF-grade interconnection quality:
Tek AM503 – 1 MHz square
Even through it’s not factory spec, the output tracks the input well enough for my simple needs.
In preparation for the next time a task puts my head in a dark place, I got a cheap headband LED light:
Headband LED – overview
Unlike most of the others you’ll find, this one has a pair of 18650 lithium cells in the box on the back of the headband:
Headband LED – isolated cell
Contrary to what you might think, the cells are in parallel, with shorting plates connecting the battery compartment terminals. This works well for perfectly matched cells, which is not what arrives in the package.
The 3200 mA·hr capacity claimed (in one line of the product description) doesn’t match the 2200 mA·hr capacity (claimed in another line and) printed on the cells. As expected, both claims far exceed the actual 1500 mA·hr measured capacity.
LED Headband Light – 2022-01-12
The 1 A load is somewhat more than the 800 mA I measured at full brightness, but makes for easy comparisons.
I think they put the cells in parallel to reach the claimed 4-6 hours of run time, but in practice the connection discharges the better cell to match the weaker one with no assurance of equal load sharing thereafter.
So I conjured an insulator from the Box o’ Retail Clamshells:
Headband LED – cell isolator
In the unlikely event my head must remain stuck in a dark spot for longer than one cell lasts, I can move the insulator to the dead cell and continue the mission. Charging alternate cells isn’t much of a burden, either.
For unknown reasons, the (anonymous) manufacturer soldered the LED package at a jaunty angle inside the frame:
Headband LED – SMD alignment
The lens pulls in-and-out to zoom the focus. The tightest setting (all the way out) projects a bright tilted square out in front, which is somewhat unsettling.
The whole affair cost less than a pair of known-good 18650 cells from a reputable supplier, so ya get what ya get.
The top step of a folding step stool we’ve been (ab)using forever finally wore out, mostly because it was covered in vinyl and intended as a seat. We always used it as a step, despite knowing you should never stand on the top rung of a ladder: “Do not stand on or above this level”.
I tossed the ripped vinyl and warped particle board, cut a random chunk of wood-textured paneling (which Came With The House™) to fit, match-drilled four holes, and it looks OK:
Folding step stool – reseated
The original seat / step / whatever used press-fit studs with a flat flange covered by the vinyl, but I just slammed 10-32 tee nuts into the paneling:
Folding step stool – tee nut installed
That’s a ring of low-strength threadlock around the inside of the nut; I do not expect the screws to come out ever again.
I cut the screws to length with a Dremel cutoff wheel using a slightly shortened tee nut as a fixture:
Folding step stool – screw shortening fixture
Not visible: the vacuum hose clamped to the vise sucking up all the abrasive + metal dust.
Good for an hour of Quality Shop Time™ on a cold winter morning!
The Tektronix AM503 manual specifies a Special Adapter to inject a signal directly into the input connector in place of the A6302 Hall probe:
Tektronix AM503 Special Adapter
The intricate Amphenol plug might still be available at some phenomenal cost, but I’m willing to just jam a pair of wires into the AM593 connector and be done with it.
I combined a pigtail BNC sporting a male connector, two 51 Ω resistors in parallel, two snippets of 18 AWG wire (an exact match for the 40 mil connector pins!) with the ends filed smooth, and some heatshrink tubing to make a roughly equivalent adapter:
Tek AM503 – Crude Special Adapter
Because the pigtail didn’t quite reach the function generator, I joined it to a longer cable with a BNC bullet, whereupon a slight tug ripped the guts out of the bullet:
BNC Bullet – failed
A closer look:
BNC Bullet – parts
The center hole comes into play with their equally craptastic BNC tee connectors.
Comparing this bullet with others from the same eBay lot shows the outer shell didn’t get quite enough crimp around the metal ring. Because it’s not an electrical connection, I eased some epoxy onto the internal shoulder where that ring seats, then slid the guts back in place.
For the first time in a loooong time I (had to) set up remote desktop sharing, starting from an existing SSH login through a single-port pinhole in an immutable router firewall.
The remote PC runs Xubuntu 20.4 LTS and I verified it already had x11vnc installed. If that’s not the case, make it so.
In order to share / control the desktop of a different user (hereinafter known as kay), I must SSH into that PC as kay. My SSH session uses public key authentication and kay has no need for outbound SSH, so just use my PC’s public key in kay‘s authorized_keys file. On the remote PC, where I am signed in as me:
cd ~
sudo mkdir /home/kay/.ssh # kay does not have a public key
sudo cp .ssh/authorized_keys /home/kay/.ssh # so just copy mine
sudo chown -R kay:kay /home/kay/.ssh # transfer ownership
sudo chmod go-rwx /home/kay/.ssh # set proper permissions
The Smell of Molten Projects in the Morning 