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

Vacuum Tube Lights: Triode

With the wrecked 5U4GB safely in the trash, I popped a smaller, somewhat less stately triode from the Big Box o’ Hollow-State Electronics and wired it up with a pair of SK6812 RGBW LEDs:

Triode – Purple-green phase

The tube’s markings have long since vanished, but, at this late date, all that matters is an intact glass envelope!

After two years, the ordinary white foam tape holding the knockoff Arduino Nano lost most of its sticktivity and easily popped off the 3D printed base:

Triode – Nano PCB – white strips

Two layers of 3M outdoor-rated foam tape clear the bottom-side components and, based on current evidence, its stickiness should stick forever more:

Triode – Nano PCB – 3M strips

The alert reader will notice the mis-soldered 1 kΩ SMT resistor above-and-right of the CH340 USB interface chip. I think those two resistors are the isolators between the 328P microcontroller and the CH340, letting you use the TX and RX lines as ordinary I/O without killing either chip.

Despite the mis-soldering, it evidently passed their QC and works fine. Seeing as how I didn’t notice it until just now, it’ll remain in place until I must open the lamp base for some other reason, which may never happen.

The data output is now on pin A5, to match the rest of the glowing widgetry:

Triode – Nano installed

Blobs of hot melt glue affix the SK6812 and wiring to the socket:

Triode – socket wiring

The original “plate cap” wiring ran directly through a hole in the hard drive platter, which I embiggened for a 3.5 mm panel-mount headphone jack. The knurled metal plug looms next to this smaller tube, but it looks better (in a techie sense) than the raw hole:

Triode – plate cap plug

Octal tubes have an opaque Bakelite base, so I devoted some Quality Shop Time™ to the post:

Triode – base tip exposed

Although I’d made a shell drill for 5U4’s base, this base was so crumbly I simply joysticked the spinning cutter around to knock off the rest of the post:

Triode – finished base

The shell drill would open the bottom to admit a bit more light. I may do that to see if it makes any visible difference.

I didn’t expect the serrations in the top mica plate to cast interesting patterns around the platter:

Triode – cyan-purple phase

Memo to Self: use the shell drill to avoid nicking the evacuation tip!

2019-03-28
Another WS2812 Failure: Broken Glass

The WS2812 under the 5U4GB full-wave rectifier tube went into pinball panic mode:

Failed WS2812 – 5U4GB Rectifier

It’s been running more-or-less continuously since late 2016, so call it

Because I’d be crazy to replace it with another likely-to-fail WS2812, I had to remove both of them before installing SK6812 RGBW LEDs and updating the Arduino Nano.

Unfortunately, I did a really good job of bonding the side light to the tube with epoxy:

Failed WS2812 – 5U4GB broken glass

The last tube manufacturing step involved flashing the getter onto the tube envelope, so as to remove the last vestige of air. Admitting air oxidizes the getter:

Failed WS2812 – 5U4GB getter oxidation

It was such a pretty tube, too …

5U4GB Full-wave vacuum rectifier – cyan red phase

2019-03-22
Sony DSC-F717 Memory Stick Socket Cable Re-Rework

Once again, the Memory Stick socket cable in my trusty DSC-F717 camera became erratic, leading to continuous C:13:01 “format error” crashes, so I tore it apart. Proceed as before, until the camera carcass disgorges the socket:

DSC-F717 – Memory Stick socket – side latches

Gently pry the metal cover outward to clear the latches along the sides:

DSC-F717 – Memory Stick socket cover latches

The cover remains held in place by two tabs inside the holes on either side of the Memory Stick contacts, one of which is already free in the previous photo:

DSC-F717 – Memory Stick socket – bottom

The small spring on the left ejects the Memory Stick and will, if suitably provoked, launch itself across the bench. Be prepared!

Use a pointy instrument to ease those tabs away from their latches and pop the top:

DSC-F717 – opened Memory Stick socket

I cleaned the contacts, not that they appeared particularly filthy, gently bent them upward by three micro-smidgens to apply a bit more pressure to the card’s contacts, and reassembled the socket in reverse order.

I put a strip of Kapton tape on the back of the cable termination paddle (shown here during the previous repair) to ensure a snug fit:

DSC-F717 Memory Stick socket – cable entry

Unfortunately, I snapped off a locking tab on one of the ribbon cable connections to the main board:

DSC-F717 – broken cable clamp

The cable threads through the middle of the clamp, which then slides into the socket and applies pressure to the contacts through the cable: no clamp, no pressure, no good.

For lack of anything smarter, I tamped the clamp into the socket and applied a strip of Kapton tape to maintain everything in more-or-less the right position:

DSC-F717 – tape-anchored cable

Definitely unpretty, but better than nothing. While I was in there, I reinforced the other connections with similar clamps.

Reassemble the camera in reverse order and it’s all good:

DSC-F717 – repaired – first image

It probably won’t last another decade, but ya never know …

2019-03-21
ESR02 Test Clips

An ANENG AN8009 multimeter recently arrived, complete with a bag of test probe parts, including a banana plug and an alligator clip crying out for a 3 mm threaded brass insert:

Makeshift test clips

A pair of them fit neatly into an ESR02 tester, where they provide tidy a low-inductance / low-capacitance “test fixture”:

ESR02 with makeshift test clips

Admittedly, loading the part-under-test isn’t a one-handed operation, but it works reasonably well.

2019-03-19
RD JDS6600 Signal Generator: Warmup Time

An RD JDS6600 Signal Generator recently arrived from around the curve of the horizon, leading me to measure its warmup time:

RDS6600 Signal Generator – Warmup plot

Looks like it’s good to go after maybe 90 minutes and, after much longer, it settles to 10 MHz +36 Hz, for a correction factor of 0.9999964 on those days when you’re being really fussy.

The need for frequencies accurate to better than 4 ppm doesn’t happen very often around here, but it’s best to be prepared. It’s amazing what you can get for under $100 these days …

I measured the frequency by zero-beating against the Z3801 GPS Frequency Standard (purple trace in the middle):

RDS6600 Signal Generator vs. Z3801 GPS Frequency Standard

Basically, trigger the scope on either trace, crank the JDS6600 frequency in 1 Hz, then 0.1 Hz steps, until the traces stop crawling past each other, and you’re done.

It’s worth noting you (well, I) must crank eleven 0.01 Hz steps to change the output frequency by about 0.1 Hz around 10 MHz, suggesting the actual frequency steps are on the order of 0.1 Hz, no matter what the display resolution may lead you to think.

The RDS6600 main PCB (Rev 15) sports a 24 MHz oscillator close to the Lattice FPGA:

RDS6600 Signal Generator – clock oscillator

The AD9850 step size worked out to 0.0291 Hz for the LF crystal tester. A 24 MHz clock would produce a 5.7 mHz step size, but that’s obviously no what’s going on. More study is indicated.

The bottom trace is the scope’s internal function generator, also set to 10 MHz. Zero-beating the JDS6600 against the scope’s output produces a similar result:

IMG_20190312_130925 – RDS6600 vs SDS2304X frequencies

The scope’s function generator actually runs at (9.999964 MHz) × (0.9999964) = 9.999928 MHz, a whopping 72 ppm low. The on-screen frequency measurements don’t have enough resolution to show the offset, nor to zero-beat it with the Z3801 input, so it’s as good as it needs to be.

The Z3801’s double-oven oscillator takes a few days to settle from a cold start, so this wasn’t an impulsive measurement. Having the power drop midway through the process didn’t help, either, but it’s March in the Northeast and one gets occasional blizzards with no additional charge.

2019-03-18
3D Printing: Erratic Z Axis Motion

From a discussion on the Makergear 3D printer forums …

A Makergear M2 user, while troubleshooting other problems, had the Z axis begin stalling and moving erratically.

the random up and down movement doesnt make any sense

It’s what happens when a stepper is mechanically overloaded: the rotor can’t turn at the commanded rate.

Start by cleaning & lubing the Z axis guide rods and leadscrew. If that solves the problem, just clean and lube a bit more often. Which none of us do until there’s a problem, of course. [sigh]

If it continues to stall, reduce the Z axis speed by a factor of four. If that solves the problem, then perhaps you tweaked the speed while you were fixing other problems and never noticed.

the technical reason why the motor would move in the opposite direction

The windings set up a rotating magnetic field which, in normal operation, drags the rotor around with it. When the rotor stalls, it vibrates back-and-forth and may wind up synchronizing with the field in the wrong direction.

Old Western movies had a similar problem with wagon wheels turning faster than the frame rate and looking like their spokes rotated backwards.

The stepper may emit horrible sounds, but stalling doesn’t do any damage to the motor or its driver.

I took the bottom of the motor apart

No sugarcoating: disassembling a stepper demagnetizes the rotor. You must buy a new Z-axis motor.

The motor is assembled with the rotor demagnetized, then it’s magnetized in place. When you take it apart, the rotor smacks into the stator, which creates a localized high-density magnetic path between the rotor poles. The rotor poles can’t support the high flux and demagnetizes.

You can put the motor together and it will “work”, in the sense that the rotor will go around, but the decreased magnetic field reduces the torque for a given winding current. You can’t increase the winding current, because the motor will overheat.

The PCB traces look mangled and warped

There’s a conformal coating over the whole PCB to prevent corrosion, so what you see is perfectly normal.

Any analysis of the data from my previous posts?

You’ve been doing a lot of fiddling with the machinery as part of finding the extruder problem, so: did you, at any time, even once, unplug / disconnect the Z axis motor when the power was turned on?

If so, that likely killed a driver transistor in that channel. Order a new RAMBo board along with the new motor.

New Rambo board came today and the z axis is working properly now.

Moral of the story: never fiddle with the electronics with the power turned on!

2019-03-14
Makergear M2: Z Endstop Crashes Firmware

From a discussion on the Makergear 3D printer forums …

A Makergear M2 user reassembled his printer, only to encounter a problem:

As soon as my z endstop triggers, the firmware resets

The Z endstop cable is plugged backwards into the RAMBo socket.

The RAMBo socket has three pins: [+ – S].

The two-wire switch cable ends in a three pin connector shell (*) with one empty contact. Unfortunately, the cable connector is not symmetric, not keyed to fit the socket latch, and easily fits into the RAMBo socket either way.

Plugged correctly, the two switch wires go to the [- S] socket pins, putting the [+] socket pin in the empty contact.

If the cable is plugged backwards, the two switch wires go to the [+ -] pins, putting the [S] pin in the empty contact.

Plugged backwards, when the switch trips, it shorts the power supply to ground. Unpleasant consequences ensue.

(*) I’d be unsurprised to discover a machine with a two-wire switch cable ending in a two-pin connector shell. Those must plug into the [- S] pins, leaving the [+] pin waving in the breeze.

2019-03-13