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.

Category: Electronics Workbench

Electrical & Electronic gadgets

Mesa 5i25 Superport: Reflash and Step-Direction Pin Swap

For reasons lost in the mists of time, the DB-25 pinout used in the Sherline CNC Driver Box is kinda-sorta the same as everybody else’s DB-25 pinout, with minor difference of swapping the Step and Direction pins on each axis. This made no difference with the LinuxCNC parallel port driver, because (nearly) all pins are alike to it, but having recently found the Mesa 5i25 Everything I/O card and being desirous of upgrading to the latest & Greatest LinuxCNC, I figured why not throw all the balls in the air at once?

Although it’s theoretically possible to recompile the FPGA source code to swap the pins, the least horrible alternative was converting a null modem (remember null modems?) into a passthrough pinswapper:

DB-25 Parallel Adapter - Step-Direction pin swap — DB-25 Parallel Adapter – Step-Direction pin swap

Make sure you put jumper W2 in the DOWN position to route pins 22-25 to DC ground, rather than +5 V. W1 does the same for the internal header, herein unused, but it’s in the same position just for neatness.

Similarly, put both W3 and W4 in their UP position to enable +5 V tolerance, connect the pullups to +5 V, and enable the pullups, thereby keeping the Sherline logic happy.

Jumper W5 must be UP in order to have the thing work.

The relevant diagram:

Mesa 5i25 - jumper locations — Mesa 5i25 – jumper locations

Flashing the 5i25 with the Probotix PBX-RF firmware produced the best fit to a simple parallel port:

sudo mesaflash --verbose --device 5i25 --write 5i25/configs/hostmot2/5i25_prob_rfx2.bit
sudo mesaflash --verbose --device 5i25 --reload

The mesaflash utility and all the BIT files come from their 5i25.zip file with all the goodies.

The Gecko G540 pinout came in a close second and, should the Sherline box go toes-up, I’ll probably replace it with a G540 and (definitely) rewire the steppers from Sherline’s unipolar drive to bipolar drive mode.

The 5i25 pinout now looks like this:

halrun

halcmd: loadrt hostmot2
Note: Using POSIX realtime
hm2: loading Mesa HostMot2 driver version 0.15

halcmd: loadrt hm2_pci
hm2_pci: loading Mesa AnyIO HostMot2 driver version 0.7
hm2_pci: discovered 5i25 at 0000:04:02.0
hm2/hm2_5i25.0: Low Level init 0.15
hm2/hm2_5i25.0: 34 I/O Pins used:
hm2/hm2_5i25.0:     IO Pin 000 (P3-01): IOPort
hm2/hm2_5i25.0:     IO Pin 001 (P3-14): PWMGen #0, pin Out0 (PWM or Up) (Output)
hm2/hm2_5i25.0:     IO Pin 002 (P3-02): StepGen #0, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 003 (P3-15): IOPort
hm2/hm2_5i25.0:     IO Pin 004 (P3-03): StepGen #0, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 005 (P3-16): PWMGen #0, pin Out1 (Dir or Down) (Output)
hm2/hm2_5i25.0:     IO Pin 006 (P3-04): StepGen #1, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 007 (P3-17): IOPort
hm2/hm2_5i25.0:     IO Pin 008 (P3-05): StepGen #1, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 009 (P3-06): StepGen #2, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 010 (P3-07): StepGen #2, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 011 (P3-08): StepGen #3, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 012 (P3-09): StepGen #3, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 013 (P3-10): IOPort
hm2/hm2_5i25.0:     IO Pin 014 (P3-11): Encoder #0, pin A (Input)
hm2/hm2_5i25.0:     IO Pin 015 (P3-12): Encoder #0, pin B (Input)
hm2/hm2_5i25.0:     IO Pin 016 (P3-13): Encoder #0, pin Index (Input)
hm2/hm2_5i25.0:     IO Pin 017 (P2-01): IOPort
hm2/hm2_5i25.0:     IO Pin 018 (P2-14): PWMGen #1, pin Out0 (PWM or Up) (Output)
hm2/hm2_5i25.0:     IO Pin 019 (P2-02): StepGen #4, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 020 (P2-15): IOPort
hm2/hm2_5i25.0:     IO Pin 021 (P2-03): StepGen #4, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 022 (P2-16): PWMGen #1, pin Out1 (Dir or Down) (Output)
hm2/hm2_5i25.0:     IO Pin 023 (P2-04): StepGen #5, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 024 (P2-17): IOPort
hm2/hm2_5i25.0:     IO Pin 025 (P2-05): StepGen #5, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 026 (P2-06): StepGen #6, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 027 (P2-07): StepGen #6, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 028 (P2-08): StepGen #7, pin Step (Output)
hm2/hm2_5i25.0:     IO Pin 029 (P2-09): StepGen #7, pin Direction (Output)
hm2/hm2_5i25.0:     IO Pin 030 (P2-10): IOPort
hm2/hm2_5i25.0:     IO Pin 031 (P2-11): Encoder #1, pin A (Input)
hm2/hm2_5i25.0:     IO Pin 032 (P2-12): Encoder #1, pin B (Input)
hm2/hm2_5i25.0:     IO Pin 033 (P2-13): Encoder #1, pin Index (Input)
hm2/hm2_5i25.0: registered
hm2_5i25.0: initialized AnyIO board at 0000:04:02.0

P3 is the DB-25 on the back panel and P2 is the internal IDC header.

2021-02-23

X10 RR501 Transceiver: Heat Death

Must be something in the air:

X10 RR501 Transceiver – overheated Zener

Another overheated Zener in another shunt power supply!

This BZY97C is still a diode, although I didn’t test its 68 V breakdown spec. I have no idea what they’re doing with that much juice inside an X10 RF box and have nowhere near enough interest to find out.

It still doesn’t work after a Laying On of Hands: out it goes.

2021-02-18
Fuvaly Bucked Lithium AA Cells

Behold lithium battery technology, a USB charger, and a buck voltage converter mashed into an AA alkaline package:

Fuvaly Bucked Lithium AA – label

Those are two of a quartet bought from a randomly named Amazon seller to appease my ~~ancient~~ ~~venerable~~ classic Sony DSC-H5’s need for more voltage than new and freshly charged NiMH AA cells can provide for more than a few tens of minutes.

The label claims 1500 mA·h, not the 1120 mA·h I measured:

Fuvaly Bucked Li AA – mAh – 2021-02

My numbers would be higher with a load less than 500 mA. I doubt the 2.5 A maximum current rating.

The claim of 2.25 W·h is rather optimistic:

Fuvaly Bucked Li AA – 2021-02

Back of the envelope: 2.25 W·h at 1.5 V equals 1.5 A·h, all right. If you squint carefully, though, the output voltages run around 1.4 V, some of which is surely IR drop in my battery holder & test wiring, but it still knocks nearly 10% off the wattage and doesn’t seem to add to the runtime.

The camera’s battery charge indicator will obviously show Full right up until it shuts off, but I’ve always carried a spare pair of cells in my pocket anyway.

Recharging them with a USB meter in series required 425 to 600 mA·h at about 4.8 V, so about 2.5 W·h.

Enlarging the instructions from the back of the box, should they become useful:

Fuvaly Bucked Lithium AA – Instructions

Nowhere does the package mention the “brand name”, manufacturer, specifications, or much of anything substantial. I suppose anybody selling white-label products appreciates this level of detail.

2021-02-15
Audio Amp vs. Bananas

A low-end audio power amp destined for a pair of ancient-yet-still-serviceable speakers arrived, but attempting to poke wires through the side holes of the banana jacks showed they were oriented in random directions. Back in the day, banana jacks had D-shaped shafts fitted into D-shaped panel holes, but those days are gone.

A few minutes with screwdriver, wrench, and (tiny) punch sufficed to line up the holes for E-Z poking:

Fosi audio amp – jack alignment

Despite the new convenience, I decided to solder banana plugs to the speaker wires, leading to the discovery my few remaining plugs came from the very bottom of the usability barrel:

Cheap banana plug – solder side

I have no idea how one might affix a wire to that blank stub, but poking a small center drill into the brass lump produces an easily solderable recess:

Cheap banana plug – center drilled

Dab with flux, tin, insert wire, add solder, repeat with all four plugs, and I’m set with a boomin’ system.

2021-02-04
LED Bulb: Mechanical FAIL

Replacing the second torchiere lamp shade required unscrewing its 100 W equivalent LED bulb, which required far too many turns and eventually felt sufficiently wrong to reveal the problem:

LED Bulb – unscrewed base

The entire metal base shell unscrewed from the plastic housing and twisted off the lead from what looks like a PTC fuse in series with the center contact; the cute little pigtail effect suggests I’ve wrecked the epoxy-to-wire seal.

It had a five year warranty which, alas, expired three years ago. This style of bulb has fallen out of favor, so I may as well get some Quality Shop Time out of it.

I don’t know how the factory machinery attached the lead to the contact button, but I’m going to go primal on it with some solder. The trick will be soldering it after assembly, so the first step is to drill through the middle of the button.

Grab it nose-down in the Sherline’s three-jaw chuck, flip it over, grab the chuck in the drill press vise, line it up, center-drill the button, then drill right through that sucker:

LED Bulb – base drilling setup

Of course, the contact came loose from the base, because I pretty much drilled right through the rivet flange holding it in place:

LED Bulb – removed center contact

Nothing a dab of epoxy can’t fix, though. I scuffed up the outside of the contact to remove the nickel (?) plating and expose the underlying brass to improve its solderability.

After the epoxy cured, align wire with hole, screw the base onto the lamp shell, and it’s ready for soldering:

LED Bulb – base ready for solder

The hole is way too large for the wire, but I wasn’t about to wreck a tiny drill on what might have been a weld nugget. In any event, the bigger the blob, the better the job:

LED Bulb – soldered base

Just like light bulb bases used to look, back in the day.

With a bit of luck, it’ll sit in that socket for another seven years.

It could happen, ya never know.

2021-02-03
Gyros Miniature Circular Saw Blade & Mandrel Tinkering

The Small Envelope o’ Slitting Saw Blades also disgorged several Gryos Ultra-fine blades and their mandrel with a broken screw jammed in place. Unlike similar Dremel-ish cutoff wheels with a mandrel threaded M2×0.4 mm, these blades have a 1/16 inch = 64 mil hole fitting the mandrel’s screw:

Gyros mandrel – broken screw size

The 1-72 brass screw came heartbreakingly close to fitting and the M2 SHCS obviously won’t play. I can’t measure super-fine threads, but I can count: 16 threads on the stub occupy about the same distance as 18 threads on the 1-72 screw, so 72 × 8 / 9 = 64 tpi and it’s a 1-64 screw, not the far more standard 1-72.

The blade hole just barely fit a #51 = 67 mil drill and measuring my assortment of mandrels produced one with the only M1.8×0.35 (OD = 71 mil) screw I’ve ever seen, so I drilled the blade with a #50 = 70 mil drill:

Gyros miniature saw blade – hole enlarging

Should the oddball screw in that mandrel break, the next step will be a #48 = 76 mil drill to fit the blade around the M2×0.4 screw for cheap and readily available mandrels.

So, being left with a broken screw stub in the original Gyros mandrel, I soaked the scene in Kroil overnight, then applied a tiny screw extractor with amazingly good results:

Gyros mandrel – broken screw extraction

I did eventually find one 1-64 screw in the Big Box o’ Tiny Screws, although its infinitesimal head seems intended for gentler duty than clamping a saw blade to the end of a whirling shaft.

Hand-held Dremel mandrels have, as far as I can tell, no particular runout specs, so chucking them in a Sherline spindle collet pretty much guarantees only a few teeth on one side of the saw will do all the cutting. Which, I hope, will suffice for my simple needs.

2021-02-01
Astable Multivibrator: Red RGB Piranha

A red LED has a sufficiently low forward voltage to run with a MOSFET astable multivibrator and a pair of run-down AA alkaline cells:

Astable AA Alkaline – red

The red LED is actually part of an RGB Piranha, just to see how it compares to an as-yet-unbuilt version with a single red LED in the same package.

The LED drops 1.9 V of the 2.75 V from the mostly used-up AA cells:

Astable Piranha Red – 2.75 alkaline – V LED

The original 33 Ω ballast resistor showed a peak current of 11 mA in a 30 ms pulse:

Astable Piranha Red – 2.75 alkaline – V 33 ohm

Replacing it with a 12 Ω resistor boosts the current all the way to 12 mA:

Astable Piranha Red – 2.75 alkaline – V 12 ohm

The 2N7000 gate sees a just bit more than 2 V, barely enough to get the poor thing conducting, which makes the ballast resistor mostly decorative. The MOSFET datasheet puts its 1 mA threshold somewhere between 0.8 and 3 V, so it could be worse.

Keep in mind the DSO150’s 1 MΩ input impedance sat in parallel with the 1 MΩ gate pulldown resistor forming the RC differentiator when I measured the gate voltage; I’ll leave the simulation as an exercise for the interested reader. The blinks were noticeably dimmer and perhaps a bit shorter, although eyeballometric calibration is notoriously hard.

The slightly revised schematic-layout doodle stacks the transistors along the negative bus bar:

Astable wiring layout – stacked 2N7000

Flipping the bottom transistor over to snuggle the two timing caps next to each other would eliminate the long jumper wire and probably look better.

2021-01-21