Folding Step Stool Re-seating

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
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
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
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!

Tektronix AM503: Special Adapter and Failed BNC Bullet

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
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
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
BNC Bullet – failed

A closer look:

BNC Bullet - parts
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.

Yak shaving in full effect!

XFCE: Remote Desktop via X11vnc Through an SSH Tunnel

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

From my local PC, I can now SSH into the remote PC as kay and start x11vnc through the SSH tunnel:

ssh -v kay@remote.address -L 5900:localhost:5900 "x11vnc -display :0 -noxdamage -ncache 10 -ncache_cr -nopw"

Still on my PC, aim a VNC client at the local end of the tunnel:

novnc localhost:5900

Using novnc presents the remote desktop as a web page in a browser, although you may prefer something more traditional.

Somewhat to my surprise, It Just Worked™.

Blog Summary: 2021

The overall page view count may be down, but people have been replacing water heater anode rods at an increasing pace:

Home page / Archives23775
Water Heater Anode Rod Access Done Right8432
CNC 3018-Pro: GRBL Configuration5301
G-Code and M-Code Grand Master List5049
Why You Need a 6-Point Socket to Remove a Water Heater Anode Rod4300
American Standard Elite Kitchen Faucet Disassembly2621
Toyota Sienna: ABS Trouble Codes2531
Raspberry Pi: Forcing VNC Display Resolution2011
CNC 3018-ProXL: Y-axis Extension1641
Subaru Forester Fuse Boxes1276
Broom Handle Screw Thread: Replacement Plug1239
Removing a Water Heater Anode Rod1221
Auto-V.I.N Gauge Scam1029
Low Budget Bench Power Supply984
CNC 3018-Pro: DRV8825 Hack for 1:8 Microstep Mode980
Kensington Expert Mouse Trackball: Scroll Ring Troubles929
Whirlpool Water Heater “Lifetime” Warranty: The Good and the Bad917
Digital Tattoo Power Supply: Polarity Doesn’t Matter912
Bed Bugs: Thermal Kill908
Review Phreesia Authorization834
Huion H610Pro (V2) Tablet vs. Ubuntu 18.04821
Kenmore 158.17032 Handwheel Clutch Disassembly799
Shimano SPD Pedals: Creaking Resolved788
2000 Toyota Sienna: Replacing the Bank 1 Sensor 2 Oxygen Sensor753
Schwab / Symantec VIP Access vs. Yubikey751
Toyota Sienna: Rear ABS / Speed Sensor Failure729
HP-48GX Calculator Disassembly: Case Rivets688
Reversible Belt Buckle: Post Restaking683
Kensington Expert Mouse Scroll Ring Fix629
Makerbot-style Endstop Power Adapter for Protoneer Arduino CNC Shield616
Displaying Variables in Gnuplot614
Kohl’s Guest WiFi Terms & Conditions: The Short Version613
Replacing Phil Wood Hub Bearings595
Magnesium Water Heater Anode Rod: Seven Years Later576
Adding a Device to LTSpiceIV564
Philips Sonicare Essence 5000: Battery Replacement550
Browning Hi-Power Magazine Dimensions545
MPCNC: Emergency Stop / Feed Hold / Resume Pendant544
Raspberry Pi Interrupts vs. Rotary Encoder538
CNC 3018-Pro: Home Switches534
Resistance Soldering: Transformer510
Adafruit Touch-screen TFT LCD Rotation489
Quick-and-easy IR-passing / Visible-blocking Optical Filter476
Dis-arming a Steelcase Leap Chair471
Icecast and Ezstream Configuration470
Why You Shouldn’t Use Heat Pumps in the Northeast US465
Baofeng UV-5R Squelch Settings460
Mini-Lathe Tailstock: Alignment449
Homebrew Magnetizer-Demagnetizer446
Arduino Serial Optical Isolator444
Mysterious Noise in Toyota Sienna Minivan: Fixed!444
Baofeng UV-5: Squelch Pop Suppression434
bCNC Probe Camera Calibration432
Demolition Card GTA 5-10-9431
Multimeter Range Switch Contacts: Whoops!425
Realigning Tweezer Tips421
Schwalbe Marathon Plus and Michelin Protek vs. Glass Chip418
Kenmore Model 158 Speed Control: Carbon Disk Replacement417
Kenmore Electric Dryer: Power Resistor Replacement416
Old Kenmore Sewing Machine Foot Control Repair414
Closing the Dmesg Audit Firehose400
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.

Auvon TENS/EMS: Modulation Waveforms

These scope screen shots use the same test setup as the pulse measurements:

Auvon AS8016 - test setup
Auvon AS8016 – test setup

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.

Patterns 1 through 16 correspond to the TENS (Transcutaneous Electrical Nerve Stimulation) label and are intended for pain relief / suppression; they should not make your muscles twitch.

P1 – Continuous comfortable tingling.

Continuous 200 µs pulse at 87 Hz

Auvon M01 Pulse
Auvon M01 Pulse

P2 – Comfortable tingling and pulsing sensation.

Continuous 100 µs pulse at 48 Hz

Auvon M02 Mod
Auvon M02 Mod

P3 – Comfortable rhythmic tingling.

Blocks of 300 ms on/200 ms off, with 150 µs pulse at 48 Hz

Auvon M03 Mod
Auvon M03 Mod

P4 – Continuous comfortable tingling.

Continuous 100 µs pulse at 48 Hz

Auvon M04 Pulse
Auvon M04 Pulse

P5 – Comfortable and slow tingling firstly, then the frequency is significantly increased, and it becomes a noticeable tingling sensation.

Continuous 250 µs pulses, stepping from 10 to 102 Hz and back down

Auvon M05 Pulse
Auvon M05 Pulse

P6 – Low frequency beating with a slight tingling sensation.

Continuous 250 µs pulses at 2 Hz

Auvon M06 Mod
Auvon M06 Mod

P7 – Low frequency slight beating firstly and then continuous comfortable tingling.

Bursts of 150 µs pulses for 3 s separated by isolated 200 µs pulses

Auvon M07 Mod
Auvon M07 Mod

P8 – Low frequency slight beating firstly and then comfortable pulsing sensation.

Bursts of 150 µs pulses for 3 s separated by isolated 200 µs pulses. Seems identical to P7, although the bursts may be slightly different.

Auvon M08 Mod
Auvon M08 Mod

P9 – Comfortable tingling from shallow to deep with 3-4 seconds pause.

Auvon M09 Mod
Auvon M09 Mod

P10 – Comfortable pulsing sensation from shallow to deep with 3-4 seconds pause.

Auvon M10 Mod
Auvon M10 Mod

P11 – Variable comfortable tingling, slight beating and scrapeing [sic] sensation.

Auvon M11 Mod
Auvon M11 Mod

P12 – Comfortable slight tingling from shallow to deep with 3-4 seconds pause.

Auvon M12 Mod
Auvon M12 Mod

P13 – Comfortable tingling and pulsing sensation from shallow to more deep with 3-4 seconds pause.

Auvon M13 Mod
Auvon M13 Mod

P14 – Rhythmic continuous beating.

Much higher voltage pulses!

Auvon M14 Mod
Auvon M14 Mod

P15 – Rhythmic scrapeing [sic] sensation.

Auvon M15 Mod
Auvon M15 Mod

P16 – Quick slight beating first, then comfortable tingling.

Auvon M16 Mod
Auvon M16 Mod

Patterns 17 through 24 sport the EMS (Electrical Muscle Stimulation) label and should make your muscles twitch in various ways.

P17 – Low frequency slight beating.

Continuous 250 µs pulse with idle time at 4.8 Hz.

Auvon M17 Pulse
Auvon M17 Pulse

P18 – Low frequency beating.

Continuous 250 µs pulse at 6.8 Hz.

Auvon M18 Pulse
Auvon M18 Pulse

P19 – Beating from low frequency to a little high frequency.

Auvon M19 Mod
Auvon M19 Mod

P20 – Muscle twitches at a very low frequency. It feels like a tapping massage.

Continuous 250 µs pulse at 13.5 Hz.

Auvon M20 Pulse
Auvon M20 Pulse

P21 – This program activates the muscle in a short tingling cycle. It is smoother than P1/P2.

Auvon M21 Mod
Auvon M21 Mod

P22 – This program gently warms up the muscles prior to exercise; it feels like a rhythmic massage. Increase intensity until you get a strong but comfortable muscle movement.

Auvon M22 Mod
Auvon M22 Mod

P23 – This program uses a pulse frequency appropriate to fast twitching muscle fibers. It improves their anaerobic capacity and is used for improving maximum muscle strength.

Auvon M23 Mod
Auvon M23 Mod

P24 – This program gently warms up the muscles prior to exercise; it feels like a rhythmic beating and comfortable tingling. Increase intensity until you get a strong but comfortable muscle movement.

Auvon M24 Mod
Auvon M24 Mod

Despite the icons on the unit’s display, the manual suggests you can apply pretty nearly any pattern to any muscle, but now we all know what’s coming out of those jacks …

Auvon TENS/EMS: Pulse Waveforms

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:

Auvon AS8016 - test setup
Auvon AS8016 – test setup

The simplest bipolar pulses always start with the negative phase. The shortest pulse width is 100 µs:

Auvon M02 Pulse
Auvon M02 Pulse

And 150 µs:

Auvon M03 Pulse
Auvon M03 Pulse

And 200 µs:

Auvon M01 Pulse
Auvon M01 Pulse

Up to 250 µs:

Auvon M06 Pulse
Auvon M06 Pulse

Some modes have a short zero-voltage pause between the negative and positive phases:

Auvon M17 Pulse
Auvon M17 Pulse

The pause can be the same duration as the negative and positive phases:

Auvon M14 Pulse
Auvon M14 Pulse

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.