ESR02 Test Clips
Posted by Ed in Electronics Workbench on 2019-03-19
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:
A pair of them fit neatly into an ESR02 tester, where they provide tidy a low-inductance / low-capacitance “test fixture”:
Admittedly, loading the part-under-test isn’t a one-handed operation, but it works reasonably well.
RD JDS6600 Signal Generator: Warmup Time
Posted by Ed in Electronics Workbench, Science on 2019-03-18
An RD JDS6600 Signal Generator recently arrived from around the curve of the horizon, leading me to measure its warmup time:
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):
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:
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:
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.
Turtles!
Posted by Ed in Photography & Images, Recumbent Bicycling on 2019-03-17
Spotted in Lake Walton on an out-and-back ride to the Hopewell Junction Depot end of the rail trail:
Mary counted & guesstimated fifty turtles in the backwater.
They’re the snuggliest turtles I’ve ever seen:
Taken with the Pixel XL at maximum zoom, hence the gritty overpixelization.
Bird Box: Flowing Ice Sheet
It’s early springtime in the Hudson Valley:
The birds have been making companionable springtime noises, but it’ll be a while before the nesting season starts up.
Taken with the DSC-H5, diagonally through two layers of 1955-ish window glass.
Monthly Image: Cutting Board Shadows
Posted by Ed in Home Ec, Photography & Images on 2019-03-15
Seen after topping bowls of chili late on a wintry day:
Late afternoon sunlight streams across the living room and through the kitchen doorway to sidelight cheddar cheese crumbs on the far side of the kitchen.
There’s also one magic wintry night when the full moon aligns with the front doorway to light the entire hallway floor for a few Stonehenge moments. It’s always a delightful surprise, even though I’m sure it’s predictable.
3D Printing: Erratic Z Axis Motion
Posted by Ed in Electronics Workbench, Machine Shop on 2019-03-14
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!
Makergear M2: Z Endstop Crashes Firmware
Posted by Ed in Electronics Workbench, Machine Shop on 2019-03-13
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.
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