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:
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:
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:
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:
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:
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:
A closer look:
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:
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
Why You Shouldn’t Use Heat Pumps in the Northeast US
Baofeng UV-5R Squelch Settings
Mini-Lathe Tailstock: Alignment
Arduino Serial Optical Isolator
Mysterious Noise in Toyota Sienna Minivan: Fixed!
Baofeng UV-5: Squelch Pop Suppression
bCNC Probe Camera Calibration
Demolition Card GTA 5-10-9
Multimeter Range Switch Contacts: Whoops!
Realigning Tweezer Tips
Schwalbe Marathon Plus and Michelin Protek vs. Glass Chip
Kenmore Model 158 Speed Control: Carbon Disk Replacement
Kenmore Electric Dryer: Power Resistor Replacement
Old Kenmore Sewing Machine Foot Control Repair
Closing the Dmesg Audit Firehose
Blog Page Views
That adds up to 200 k page views from 122 k visitors, for an average of 1.6 pages / visitor, down slightly from last year. For a variety of reasons, I wrote only 242 posts over the course of the year, so more folks read only the single post matching their search terms.
To give you an idea of how awful online advertising has become, WordPress shoveled 817 k ads at those readers, slightly more than four ads per view. Given the toxicity of online advertising, I just started paying $50/year for a “personal” plan to get a few more gigabytes of media storage, which also let me turn off the ads. Most of you won’t notice, as you already run ad blockers, but it will calm the results for everybody else.
Fortunately, losing the $250 / year income from those ads won’t significantly affect my standard of living.
The sweep speeds run much slower to capture the complete envelope, which can be up to a minute long, with enough left over to show the end of the previous sequence and the start of the next. The Moire patterns come from the scope sampling rate, the display resolution, or changes in the pulse repetition frequency. Blame Siglent for not making the scope’s digital data accessible through the network; screen shots are the best I can do.
The descriptive headings for each screen shot come from The Auvon AS8016 Fine Manual, a PDF version of which you can get from Auvon’s support staff by asking nicely. I identify the modes as Mxx, rather than their Pxx, for reasons that made sense at the time.
The Auvon AS8016 TENS/EMS unit produces bipolar pulses with no net DC offset, so the UI controls the negative and positive amplitudes equally. The range has 20 steps, with the screen shots here set to 10 units. The actual output voltage depends on the mode, with some modes producing a peak voltage well above the others at the same UI setting.
It’s worth noting the effect comes from current passed through skin and muscle, rather than voltage applied to it. The test setup uses a 500 Ω resistance to make the current vary linearly with the voltage (which is definitely not the case with human bodies): a 20 V pulse passes 40 mA through the resistor:
The simplest bipolar pulses always start with the negative phase. The shortest pulse width is 100 µs:
And 150 µs:
And 200 µs:
Up to 250 µs:
Some modes have a short zero-voltage pause between the negative and positive phases:
The pause can be the same duration as the negative and positive phases:
Some modes have pulses starting with the positive phase, others switch the leading phase during the course of the output modulation.
My casual survey of the consumer-grade field suggests the pulse waveform has less to do with well-tested effects and more to do with marketing or straight-up woo, but I admit to being a cynic.