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.

Author: Ed

  • SPICE Crystal Model

    Linear Technology’s LTSpice generic capacitor model has all the parts you need to synthesize a crystal, which is pointed out in the help file and various spots around the web. What’s missing is the relation between all the parts and the values you have in hand for an arbitrary crystal.

    SPICE Capacitor Model
    SPICE Capacitor Model

    The crystal capacitor model looks like this…

    Cpar (usually C0) along the right edge is the inter-electrode capacitance, on the order of a few pF.

    Rpar (usually R0) along the left edge is the parasitic resistance across the case, on the order of hundreds of MΩ.

    The RCL string in the middle is the “motional” part of the crystal model, generally found with a subscript “m” in the specs.

    • Rser (Rm or ESR) is on the order of 100 Ω
    • Capacitance (Cm) is the motional capacitance, on the order of fF (that’s femtofarad: 10-15)
    • Lser (Lm) is tens to thousands of mH
    • RLshunt is something I haven’t seen in any other model and, in fact, it doesn’t appear in the properties panel.
    Crystal Properties
    Crystal Properties

    Now, the part I screwed up is that the capacitor’s value (the number appearing on the schematic) is Capacitance (in the angle brackets that royally screw up WordPress HTML), not Cpar. So the crystal capacitor properties panel looks like this…

    That models a 10 MHz crystal, taken directly from a sidebar in Refinements in Crystal Ladder Filter Design by the legendary Wes Hayward W7ZOI, in the June 1995 issue of QEX.

    Guess what? Plug it into a model of his crystal-measuring circuit and it works exactly like he says it should. No surprise there…

    SPICE has a bit of trouble simulating high-Q oscillators; they tend to not start up properly. If nothing seems to be happening, wait for a few tens-to-hundreds of milliseconds before despairing. Try chopping Rser down by a factor of two or four to see if that improves its disposition.

    You could try injecting a few (hundred thousand) cycles of a kickstart signal, but that’s fraught with peril: you’re simulating something even further from reality than usual.

    Memo to Self: You can rename the cap from C2 (or whatever) to X1 (or whatever) and everything still works fine.

  • Long Out of Warranty

    Found this on the long-disused stage of the former Martha Lawrence School, now the St Francis Hospital Daycare Center, hosting the polling place where I was serving as an Election Inspector. It’s a bit hard to read, even in the larger version, but I thought a one-year warranty etched into a brass plate was interesting; it’s screwed right to the side of the dimmer panel.

    Lighting Switchboard Warranty Placard
    Lighting Switchboard Warranty Placard

    The warranty provisions require that the dimmer panel be properly maintained, regularly used, and kept clean. As you can easily see, it’s been a long while since anyone has put on a stage production.

    I think the warranty ran out right around the time I was born, but I could be off by a decade or two either way.

    Lighting Switchboard Dust Accumulation
    Lighting Switchboard Dust Accumulation

  • Electronic Voting Machines: Another Reason for Distrust Thereof

    Voting Machine LCD Touchscreen Miscalibration
    Voting Machine LCD Touchscreen Miscalibration

    This is on the “control panel” side of the Sequoia ImageCast Ballot Marking Device voting machines used in Dutchess County. I put my finger in the middle of the CLOSE POLL button and the panel misread a press on the REPORTS button.

    That’s one of several misreadings of the day. Earlier, while setting up the machine for the day, it misread horizontally and gave me a STATUS report instead of a ZERO report.

    Last year the same sort of thing happened. It’s always explained as “being out of calibration”, which makes me wonder just exactly when the panels are calibrated and what the criteria for success might be.

    One of the few good things to come out of having a totally dysfunctional State Legislature is that New York has managed to delay and stall and fumble around until other states demonstrated the utter stupidity of direct-recording, no-paper-trail electronic voting machines. The ImageCast machines are a spectacular boondoggle, but far less catastrophic than what we’ve seen in Florida, Ohio, California, and …

    Oh, and after a 16-hour shift as a BMD Election Inspector, exactly zero handicapped voters (actually, any voters) took advantage of the machine to cast their vote. A report from someone who’s in a position to know says that in the last election, the bottom line was $250 per vote on the ImageCast machines. I think that’s probably low.

    My tax dollars at work, fer shure!

  • Connectivity Options: Evolution Thereof

    We stayed at the Syracuse Sheraton while chaperoning a Marching Band trip, which led to meals in the Regents Ballroom, a large space (potentially) divided in three parts by the usual folding partitions. The wall in each section had a bank of RJ-11 and -45 jacks…

    Hotel Ballroom Phone and Data Jacks
    Hotel Ballroom Phone and Data Jacks

    Obviously, back in the day, a single room with 25 Phone jacks and one (red) Data jack made perfect sense. Or maybe the ballroom has 75 phones lines and three Data connections? Hard to say.

    Judging from the overall crud accumulation, the jacks aren’t getting much use. I wonder if it was originally set up so they could run a boiler-room operation out of the hotel ballroom?

  • Insurmountable Opportunity

    Ten Pound Hershey Bar
    Ten Pound Hershey Bar

    Several decades ago I got my esteemed wife a ten-pound Hershey bar for Christmas. She said that was a thoughtful gift, exactly what she wanted, and if I ever did that again, she would kill me.

    Turns out that I’d gotten such a bar myself, many many years ago…

    These days, of course, the biggest Hershey’s Chocolate bar you can get is a measly five pounds.

  • More Firefox Update Restart Foolishness

    Guess what? Update Firefox to 3.0.15 in Xubuntu and we’re back to the continuous restart reminder situation I mentioned there.

    Same fix applies this time, too.

  • American Standard Faucet Aerator Disassembly

    American Standard Faucet Aerator Disassembly

    Aerator filter disassembly
    Aerator filter disassembly

    I’m sure they have more different versions of these things than anyone can count, but when I unscrewed the kitchen sink aerator, this is what I found inside.

    The yellow plastic filter actually has two parts, held together by a minuscule clickstop on the central post. You can pry the whole thing off the main body with your thumbnail or, as in the photo, just pop the top screen off.

    Rinse the grit off the screen, snap it back together, screw everything back onto the spout. Done!

    It’s amazing how much grit accumulates downstream of the whole-house water filter. On the other paw, having just replaced the water heater, I’m not that amazed.