Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Here’s the status of the AA NiMH packs I’ve been using with the radios on our bikes, plus three packs I made up last year and have been keeping on the desk to measure their long-term storage characteristics. Click for more detail.
Bike Radio Pack Status – 2010-03
The “Tenergy 09 x” packs are new & unused with, frankly, disappointing capacity of about half their 2.6 Ah rating. That’s not much better than the used Tenergy packs (T9x and RTU x), which is either a Good Thing (they have good long-term stability) or a Bad Thing (they’re grossly over-rated to begin with).
The two Duracell packs are far better than any of the Tenergy packs.
The three 6-cell packs along the bottom are fading fast.
The previous test runs are there, albeit with a 1 A discharge.
This season I’ll use some Li-Ion packs that weigh twice as much with three times the capacity… plus a built-in charge gauge, pessimistic though it may be.
A comment on yesterday’s post about quartz crystal measurements prompted me to destroy a crystal in the name of science…
The question is, what effect does exposing a crystal to the air have on its performance? I would have sworn it would never work right again, because it’s normally running in an inert atmosphere and maybe a partial vacuum. One measurement being worth a kilo-opinion, here’s what happened.
I picked random crystal from the bottom of the crystal box, based on it having a solder seal that I could dismantle without deploying an abrasive cutoff wheel or writing some G-Code to slice the can off with a slitting saw. The crystal was labeled HCI-1800 18.000 MHz and probably older than most of the folks who will eventually read this… younger than some of us, though.
The center frequency is 18.0050 MHz (at this rather broad span) and it has some ugly spurs out there to the right.
A closeup of the series-resonant peak:
HCI-1800 18 MHz – Baseline BW
The bandwidth is 1.50 kHz at 17.99950 MHz at this span.
Naked HCI-1800 18.0 MHz Crystal
Then I applied a soldering iron around the seal and yanked the case off. I think that didn’t involve whacking the crystal with the case en passant, but I can’t be sure. In any event, it looks undamaged and seems to operate properly.
A pair of spring clips attach to the electrodes and hold the quartz disk in position. They’re just the cutest little things and quite unlike the other holders I’ve seen. I think the solder blobs fasten the spring ends together and don’t bond to the electrodes, but what do I know?
HCI-1800 Crystal Overview
The quartz disk has a few small chips near the edge:
HCI-1800 Crystal Edge Chips
I think those are Inherent Vice… simply because:
They’re not in a position where I could have whacked the disk and
I doubt I could whack it that delicately
Anyhow, with the can off, here’s what the series resonant peak looks like:
HCI-1800 18 MHz – Opened BW
The resonant frequency is now 17.99968, 180 Hz higher, which may be due to instability in the HP8591 spectrum analyzer’s not-stabilized-for-ten-hours ovenized oscillator. The bandwidth is 1.55 kHz, 50 Hz wider, although I think that’s one resolution quantum of difference.
Here are the two bandwidth traces overlaid.
HCI-1800 18 MHz – Overlaid BW
The peak has been centered in both, so you can’t tell they’re slightly different. The interesting point is the difference in the slope to the low-frequency side of the peak, which is slightly higher for the open-case condition. Seeing as how the missing case completely changes the usual stray capacitance situation, I’m not surprised.
Anyhow, I admit to being surprised: there’s not that much difference after opening the case. I’ll put the naked crystal in a small container in a nominally safe place for a while, then retest it to see what’s happening.
Memo to Self: A “safe place” is nowhere near the Electronics Workbench!
Here are some other naked crystals:
Naked Crystals
Notice the tarnished (presumably) silver electrodes on the crystal in the lower left. That one’s been sitting on my monitor and in other hazardous locations for a few years. I can’t find these anywhere right now, but if they turn up I’ll test them, too.
Spent some Quality Shop Time measuring an assortment of crystals, some data from which will make up a Circuit Cellar column.
And the raw numbers will come in handy one of these days, so here they are…
12 MHz Asst
HC-49/U
Co+Cc/2
2Cc
Fs
BW
Rs
ECS
1
4.85
1.47
12.000162
787.5
40.1
ECS
2
4.50
1.42
12.000150
725.0
40.1
ECS
3
4.70
1.42
12.000325
1100.0
50.0
Rs out of range
HC1
4
4.34
1.11
11.999000
600.0
36.0
HC1
5
4.24
1.06
12.000137
537.5
36.9
Sentry
6
5.14
0.96
12.000250
625.0
31.8
many spurs
11.0592 MHz
HC-49/U
1
4.90
1.42
11.059275
562.5
9.3
2
4.99
1.46
11.059112
575.0
14.7
3
4.87
1.42
11.059275
512.5
9.6
4
4.87
1.41
11.059125
550.0
10.0
5
4.29
1.43
11.058935
750.0
18.1
6
4.93
1.47
11.059000
537.5
10.7
7
4.95
1.47
11.059200
525.0
8.1
8
5.03
1.45
11.059037
575.0
11.1
10 MHz
HC-49/U
spur +150 kHz
1
2.57
1.36
9.997888
200.0
14.2
2
2.61
1.30
9.997738
225.0
16.7
3
2.75
1.30
9.997788
225.0
20.0
4
2.67
1.30
9.997750
225.0
16.1
5
2.75
1.26
9.997725
250.0
22.7
6
2.69
1.27
9.997788
225.0
21.0
7
2.69
1.26
9.997825
212.5
16.5
Circuit Cellar example
8
2.69
1.22
9.997832
212.5
18.4
9
2.72
1.24
9.997788
250.0
23.4
10
2.68
1.20
9.997738
225.0
18.0
18.43 MHz
HC-49/US
many spurs +10 +76 kHz
1
3.86
1.33
18.432425
1.56
24.1
2
3.79
1.22
18.432987
1.21
10.9
3
3.93
1.39
18.432050
2.44
46.3
4
3.97
1.40
18.431175
1.90
27.7
5
3.89
1.33
18.431888
2.11
32.2
6
3.92
1.39
18.430888
1.39
16.5
7
3.99
1.35
18.431500
1.36
11.8
8
3.97
1.35
18.431675
2.18
38.4
9
3.95
1.31
18.430512
1.30
10.1
10
4.04
1.50
18.431427
1.36
11.8
The 18.43 MHz crystals are in the short /US cans with surprisingly high stray capacitance. Their bandwidths are in kHz and all over the map, as are the series resistances. Weird. Bad crystals? Bad technique?
Frequency & bandwidth from HP8591 spectrum analyzer with a fixture similar to the K8IQY design; the bandwidths seem to come in 12.5 Hz increments despite a (very narrow) 2 kHz span. The general process is there. Resistance measured from a cermet trimpot using a multimeter good for 0.1 Ω around 10 Ω.
Crystal Test Fixture
Useful equations, with column headings in boldface:
Lead-to-can capacitance for each lead: Cc = 2Cc / 2
Lead-to-lead capacitance: Co = Co+Cc/2 – Cc/2
Circuit Q: Q = Fs/BW
Circuit resistance: R = Rs + 25 (assuming 4:1 transformers)
Mary & I did the weekly grocery run today, with a few add-on errands.
I’m (finally) shipping the Totally Featureless Clock to my friend and hauling a bag of shredded leaves (the first of a dozen) with which Mary mulches the plants in her remote garden plot. We dropped off the leaves and some garden gate fencing (from her bike), then continued on for groceries.
Trailer with Package and Shredded Leaves
Mary returned to the garden to spend the afternoon coaxing the plants to grow nicely, while I hauled the TFC (and the groceries) to the UPS inlet.
Trailer with Groceries and Package
And then I hauled the groceries home. Most of the four bags of chow fit in the trailer, with squishable fruit & veggies in the bike panniers. A whopping 13 miles, all told, but a good time was had by all.
The trouble with bicycles is that they have approximately the cargo capacity of your car’s glove box. Panniers help, but for bulk capacity you need a trailer. Think of it this way: these days, a good trailer costs maybe three or four tanks of gasoline.
If you keep coming up with reasons why you can’t get your butt on your bike and “I can’t haul X!” is one reason, a trailer might be the answer for reasonable values of X. It’s no good for plywood sheets and water heaters, but I’ve hauled plenty of other X that would ordinarily call for a car trip.
It’s an old B.O.B Yak. Works fine, tracks well, doesn’t wobble, carries more than you think possible.. Just do it!
We each put about 2000 miles a year on our bikes, most of it on errands just like this. That’s not many miles by bicycle fanatic standards, but we do lots of other stuff in addition to biking…
Search the blog for “trailer” and you’ll find a few other hints & tips.
Having mounted & wired the switches, the next step involves defining the homing sequence & configuration for each axis. All this goes in Sherline.ini and is adapted from the doc there.
The travel limits are somewhat empirical and I think the Y axis will require some adjustment due to the tooling plate switch extender gadget.
The HOME_SEARCH_VEL values may be a bit too high, given the rather lethargic 5.0 in/sec^2 acceleration I’m using for X & Y, with just 3.0 for Z. I’ve heard the occasional thwack as the switch trips, so maybe 20 mils of overtravel isn’t quite enough.
Real men have real CNC milling machines and real CNC milling machines have home switches. I have an itsy Sherline CNC mill, but now my mill has home switches just like a Real Man’s mill.
Sorta, kinda.
Truth is, I really don’t need home switches for the Sherline. I haven’t done any “production” milling with fancy fixtures, so zeroing the coordinate system to the lower-left vertex of the part-to-be-milled works reasonably well. But I figured it’d be fun to see what I was missing…
The first step was to hack another jack on the Sherline controller box and connect it to parallel port bit 10. The process is pretty much the same as I used for the probe switch jack documented there. I actually put the jack in the hole used for the power LED and drilled a new hole for the LED smack in the middle above the connector.
Sherline Controller with Probe and Home Jacks
The simplest way to do home switches is to wire them all in parallel using a single port pin. You can even wire the probe switch in parallel with home switches, too, but I figured it’d be nice to have separate jacks… and, besides, the controller still has a few port pins left.
Adding the home switches requires a few lines (adapted from there) in custom.hal that connect the sense inputs in parallel:
net homeswitches <= parport.0.pin-10-in-not
net homeswitches => axis.0.home-sw-in
net homeswitches => axis.1.home-sw-in
net homeswitches => axis.2.home-sw-in
Using the -not suffix flips the sense of the input so the signal is True when the buttons get pushed. I don’t know of any algorithmic way to determine the actual logic states for a given button configuration, so just try it, use Halmeter to see what happens, then flip as needed.
The catch with adding home (or limit) switches is that Sherline mills have an attentuated mechanical structure with no good places to affix switches. I figured a trio of microswitches and a few dollops of JB Quik epoxy would suffice; if I must remove the switches, a quick shot with a chisel should pop the epoxy right off the metal.
The microswitches have about 20 mils of overtravel. I located the switches so the actuator buttons are bottomed out against the cases with the axes at the far limits of their travels. The steppers are puny enough to stall when the mechanical bits hit their hard limits, so there’s no risk of wrecking the machinery or knocking the switches off.
The X-axis home switch goes on the right side of the table, where it contacts the Y-axis slide at the end of travel. Putting it there also means I can remove the table by simply running the leadscrew out of the nut and pulling the whole affair off to the right. I lashed the switch cable to the motor cable with (wait for it) cable ties, which is probably a Bad Idea for larger machines, but seems to be OK in this situation.
X Axis Home Switch
The Y-axis home switch goes at the rear of the machine base, aligned with the plastic bushing I put there to capture the end of the leadscrew. That’s the travel limit for the bare table, but the Sherline tooling plate sticks out another half-inch: the plate hits the column before the table hits the bushing. Alas, I use the plate a lot.
Rather than futz with an adjustable switch position, I made a removable extender. The 3 mm (1/8″ nominal) thick plastic strip has 1 mm milled off the bottom, leaving a tab on the left side that snaps over the dovetail. The screw extends down past the dovetail on the right, so the whole affair slides back & forth just enough to connect the Y-axis slide with the button. The brass tubing exactly fits the tit on the switch actuator and is urethane-glued to the strip.
It’s removable by lifting the left end and sliding the whole affair out under the leadscrew.
Y Axis Home Switch with Extender
The alternative, putting the Y-axis home switch on the very front of the base, would expose the switch & cable to all the slings & arrows of outrageous fortune to be found around the area of the countertop I use most. That may still prove to be a better location: if the back doesn’t work out, it’s easy to move.
The Z-axis switch had to go at the top-of-column mechanical limit, as homing to the downward limit of travel seemed fraught with peril. I epoxied the switch in place by clamping it to a shim atop the Z-axis slide to align the switch body, then applying gentle sideways pressure with a small screwdriver.
Epoxying the Z Axis Switch
This is what it looks like after the epoxy cured. The square key bar sticking out of the extender block clears the switch with plenty of room to spare, no matter what it looks like.
Z Axis Home Switch
The cables from all three switches go to a common junction where they’re connected in parallel to the cable leading to the green plug in the top picture.
Tomorrow, the configuration file that makes all this work…
Herewith, the discharge test results for all the generic Sony NP-FS11 battery packs I have (click for a bigger image).
Sony NP-FS11 Status – 2010-04
The five mostly overlapping upper traces consist of:
Three packs (H, K, and L) rebuilt from the eBay junkers
F rebuilt from a deader in my collection
E is an older, no-name pack that just continues to work
The rebuilt packs now have cells from batteryspace.com that are working fine: nominal capacity 600 mAh, actual around 1200 to 1400 for a parallel pair. It’s surprising to see a cell producing its rated capacity…
The two lowest traces (G & I), plus the purple trace (J) are from the eBay source. The first two are obvious junk, but pack J is actually pretty good. The fact that it’s the best of six packs from that vendor tells you all you need to know about their QC.
For those of you joining us via search engines, the rest of the story:
The Smell of Molten Projects in the Morning 