Digital Tattoo Power Supply: Polarity Doesn’t Matter

When I rewired the guts of the digital tattoo power supply to eliminate the series foot switch, I kept the original wiring polarity, with the black wire to the sleeve and the red wire to the tip:

Tattoo Digital Power Supply - internal view

Tattoo Digital Power Supply – internal view

It’s the same color code I (strongly) recommend in the Squidwrench Electronics Workshops: use any color for the ground / common wire as long as it’s black, then, if you have a red wire, use it for the positive supply. You can use yellow for the higher supply voltage, but stop being clever.

I put suitably colored Powerpoles on the far end of the cable to replace the standard tattoo machine spring clip connector, so I can attach clip leads, battery test fixtures, and so forth and so on.

We wired the supply into a clip-leaded diode measurement setup with a current limiting resistor and a pair of multimeters to measure the diode current and forward voltage, whereupon we noticed all the meters displayed negative voltages and currents.

After a frenzy of wire-checking verified their setup was all good, I forced the simplest possible test, herein recreated on my bench:

Tattoo Digital Power Supply - polarity test

Tattoo Digital Power Supply – polarity test

Which produced this display:

Tattoo Digital Supply - reverse polarity

Tattoo Digital Supply – reverse polarity


After a brief exploration of “Trust, but verify” territory, we swapped the clip leads from the power supply and continued the mission.

Back on my bench, I pulled the supply apart and measured the voltage at the jack terminals:

Tattoo Digital Power Supply - jack wiring

Tattoo Digital Power Supply – jack wiring

Still negative. Huh.

The bottom of the power supply PCB shows exactly what you should expect by now:

Tattoo Digital Power Supply - reversed color code

Tattoo Digital Power Supply – reversed color code

The red wire near the top of the board is, indeed, soldered to the trace labeled GND and goes to the jack’s tip terminal; the adjacent black wire goes to the front-panel LED. Similarly, the black wire just below it, soldered to the same trace as the yellow wire, goes to the jack’s sleeve terminal; that trace also connects to a resistor leading to the trace labeled LED+ and the LED’s red wire.

Although tattoo machines run from DC supplies, their motors or vibrators don’t depend on any particular polarity and will run fine with a backwards supply.

Resoldering the red and black wires where they should go produces the expected sign at the jack:

Tattoo Digital Supply - meter leads

Tattoo Digital Supply – meter leads

Although measuring and plotting diode voltages and currents may seem tedious, actually wiring stuff together and taking data reveals how difficult the real world can be.

I trusted the supply’s internal color code and, although I’m certain I tested the Powerpoles, I obviously didn’t notice the meter’s sign.

Memo to self: Sheesh.


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Never Antagonize Your IT Staff

A useful CallerID name that’s not actually spoofed:

Illegal Scam CallerID

Illegal Scam CallerID

I get the distinct impression there’s a disgruntled employee somewhere in their IT department and, apparently, there are more than you’d think.

Ya can’t make this stuff up …


Monthly Image: Barred Owl In Daytime

A pair of Barred Owls set up housekeeping nearby and we’ve watched them swoop down on rodents in the yard. We hope they succeed in raising their owlets!

This one kept watch on us as we cleared out a dead holly bush near the garden:

Barred Owl - daytime

Barred Owl – daytime

I took another picture at +1 EV to show more of the owl’s face; while blowing out the highlights:

Barred Owl - daytime - 1 EV

Barred Owl – daytime – 1 EV

Go, owls, go!

Taken with the Sony DSC-H5 and 1.7× teleadapter, because the Pixel phone’s camera just doesn’t have enough moxie at full zoom.

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Summer Downshift

We have several high-intensity / long-attention-span home projects scheduled this summer, all of which will keep me away from the Basement Laboratory.

We’re OK, all is right with our world, but painting rooms and yard maintenance always take way more time than they should, while having close to zero intellectual content.

Like, for example, the result of a strenuous morning devoted to removing a severely overgrown holly bush:

Mother of All Holly Bush Stumps

Mother of All Holly Bush Stumps

I’ll post odd & ends a few times a week until maybe mid-August, whereupon I should get back to more usual pursuits.

Enjoy your downtime …



Subaru Forester Relamping

Prompted by RCP’s battery misadventure, I replaced a handful of the Forester’s incandescent bulbs:

Subaru Forester 2015 - replaced bulbs

Subaru Forester 2015 – replaced bulbs

Despite what look like “squeeze here” markings, you must push the license plate bulb holders toward the center of the car:

Subaru Forester 2015 - license plate bulb holders

Subaru Forester 2015 – license plate bulb holders

They were both stuck firmly to the trim plate, so I braced a screwdriver against the outboard edge of the trim panel, after which it becomes obvious how pressing inward compresses the (plastic) spring clip so you can pull the outward side of the holder away from the hatch.

Casual searching turned up a bunch of exceedingly helpful advice for anyone DIY-ing through a Forester.

The bulbs with conical ends, known as “festoon” lamps, (unsurprisingly) come in  several lengths. The Forester bulbs are about 25 mm long, (unsurprisingly) much shorter than the 31 mm LEDs that seem to be the smallest available replacements, but (surprisingly) the socket tabs have barely enough compliance for the extra half dozen millimeters:

Subaru Forester 2015 - dome with 31 mm festoon LED bulb

Subaru Forester 2015 – dome with 31 mm festoon LED bulb

The LEDs are much much much brighter than the incandescents, although I’d prefer warm white to cool white. The cargo compartment lamp in the back is still way too dim; I don’t understand how Subaru decided on a plastic cover tinted tinted dark smoke gray.

All in all, a worthwhile upgrade!

I wonder how long they’ll last? I have one spare of each type …


Turtles All The Way Down

Spotted another big turtle ready to cross the Dutchess Rail Trail along Daley Rd:

Rail Trail Turtle - 2018-06-04

Rail Trail Turtle – 2018-06-04

This must be the best season ever for turtles crossing vast expanses of asphalt, because I don’t recall seeing this many turtles during any previous spring. Confirmation bias in full effect, to be sure.

The picture is a dot-for-dot crop from the Sony HDR-AS30V helmet camera, demonstrating why image compression has more to do with resolution than the number of dots.

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Snapping Turtle Teleportation

The dark spot in the grass, barely visible over on the left, is a dinner-plate-size snapping turtle recently teleported from the middle of Rt 376 just north of Robinson Lane:

Snapping Turtle Teleportation - Rt 376 - 2018-06-02

Snapping Turtle Teleportation – Rt 376 – 2018-06-02

The driver of the white van managed to stop both lanes during the rescue and, judging from the lack of gore, handled the snapper without incurring organic damage.

Color me impressed!


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