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.

Tag: Rants

And kvetching, too

  • TLC5916 LED Driver Current Monotonicity Hack

    TLC5916 Current Gain vs Config Code
    TLC5916 Current Gain vs Config Code

    I’m using Texas Instruments TLC5916 constant-current LED driver chips for my my friend’s Totally Featureless Clock. An 8-bit configuration value sets the output current, with the external resistor defining the maximum value as described there.

    The problem is that the current-versus-config-value curve has a non-monotonic discontinuity in the middle, where the Current Multiplier bit switches from 0 to 1. I don’t know in which alternate universe this design decision made sense, but right here and now…

    It. Does. Not.

    Why it’s a problem: the LED brightness tracks room illumination as seen by a CdS photoresistor, averaged over maybe half a minute. The brightness changes very slowly, so the jump when it goes from 0x7f to 0x80 is really eyecatching. At least to me, anyway.

    Eyeballometric measurement of the curve shows the current at 0x80 pretty much matches the current at 0x60, soooo let’s just shove the second quarter of the curve (between 0x40 and 0x7f) downward until it meets the high-current value at 0x80.

    This code does the trick:

    if ((Brightness >= 0x40) && (Brightness <= 0x7f)) {
 Brightness = 0x40 + ((Brightness & 0x3f) >> 1);
}

    Basically, that maps 0x7f to 0x5f. The output current for 0x5f is pretty close to the current for 0x80, making the step pretty much a non-issue.

    You could, if you were fussy enough, work out the actual current mapping values from the data sheet equations and make the ends match up perfectly.

  • Digital Concepts AAA NiMH Cells: Craptastic!

    The AAA cells I mentioned there bubbled to the top of the heap on my desk again, so I charged them, let them sit around for a few days to stabilize, then ran a discharge test.

    The top (black) trace is all four AAA cells in series; the two steps correspond to the two weakest cells failing. The red trace is the surviving two cells. The green trace is the strongest cell, which supplied current during all three traces.

    They’re nominally 900 mAh, but the results are pretty much what you’d expect.

    No-name AAA NiMH - Sequential Discharge
    No-name AAA NiMH – Sequential Discharge

    The most durable cell, the last one to fail with the green trace, had a capacity of a bit over 500 mAh: slightly over half the rating. The weakest cell (the first step on the black trace) failed after a mere 250 mAh.

    Junk. Pure junk. I’ll give ’em another charge just to see what happens, but don’t hold your breath anticipating a resurrection.

  • 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!

  • 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.

  • Why Friends Don’t Let Friends Use Windows For Embedded Systems

    OK, this is shooting the low-hanging fish right off the barrel (or some such mixed metaphor), but why does anybody still use Internet Explorer and Windows for embedded systems?

    cimg4138 - IE Was Unable to Link to Web PageThe proximate cause is a dead Internet link, but somebody obviously didn’t take that problem into account during the design phase. I’m sure there’s a keyboard hidden inside the box, wherever the box might be, but the rest of us are left to snicker at a jammed display.

    The problem resolved itself (or somebody plugged in the cable) by the time we walked past the display again.

  • Do Not Push The Button

    Do Not Push
    Do Not Push

    Found this in a church restroom, which is pretty much a benign public environment.

    If you put a pushbutton control at the usual place for a light switch and give it a light-switch affordance, then you shouldn’t be surprised when people push it.

    Now, if the pushbutton happens to both turn off the light and disable the automatic light function, well, that’s hardly the user’s fault, is it?

    Methinks it should be an automatic light switch with a manual override tucked inside a cover that doesn’t look at all like a pushbutton. Of course, the IR lens over the sensor would then require some up-armoring, as it’d look a lot like a button.

  • The Decline of Literacy: Part Two

    Saw this in a somewhat downscale grocery store while chaperoning a Marching Band event.

    Hand Dryer Graffiti
    Hand Dryer Graffiti

    I’d give him (it’s a mens’ restroom) some bonus points, as I think he caught and corrected the error, but then there’s that “to”. Ouch.

    I ask you, though, what grade were you in when you learned how to spell “much”? I doubt you’ve had any trouble spelling it since then.