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

  • Adafruit TFT LCD: Color Indicator Spots

    These spots might come in handy as status indicators and tiny mode control buttons:

    Resistor Color Code Spots
    Resistor Color Code Spots

    The montage is 800% of the actual 8×8 pixel size that’s appropriate for the Adafruit TFT LCD.

    They’re generated from the standard colors, with the “black” patch being a dark gray so it doesn’t vanish:

    # create resistor-coded color spots
    # Ed Nisley - KE4ZNU
    # January 2015
    
    SZ=8x8
    
    convert -size $SZ canvas:gray10 -type truecolor Res0.bmp
    convert -size $SZ canvas:brown	-type truecolor Res1.bmp
    convert -size $SZ canvas:red	-type truecolor Res2.bmp
    convert -size $SZ canvas:orange	-type truecolor Res3.bmp
    convert -size $SZ canvas:yellow -type truecolor Res4.bmp
    convert -size $SZ canvas:green	-type truecolor Res5.bmp
    convert -size $SZ canvas:blue	-type truecolor Res6.bmp
    convert -size $SZ canvas:purple	-type truecolor Res7.bmp
    convert -size $SZ canvas:gray80	-type truecolor Res8.bmp
    convert -size $SZ canvas:white	-type truecolor Res9.bmp
    
    montage Res*bmp -tile 5x -geometry +2+2 -resize 800% Res.png
    

    For a pure indicator, it’d be easier to slap a spot on the screen with the Adafruit GFX library’s fillRect() function. If you’re setting up a generic button handler, then button bitmap images make more sense.

  • Adafruit TFT Shield: Firmware Heartbeat Spot

    Being that type of guy, I want a visible indication that the firmware continues trudging around the Main Loop.  The standard Arduino LED works fine for that (unless you’re using hardware SPI), but the Adafruit 2.8 inch Touch-screen TFT LCD shield covers the entire Arduino board, so I can’t see the glowing chip.

    Given a few spare pixels and the Adafruit GFX library, slap a mood light in the corner:

    Adafruit TFT - heartbeat spot
    Adafruit TFT – heartbeat spot

    The library defines the RGB color as a 16 bit word, so this code produces a dot that changes color every half second around the loop() function:

    #define PIN_HEARTBEAT 13
    
    unsigned long MillisThen,MillisNow;
    #define UPDATEMS 500
    
    ... snippage ...
    
    void loop() {
    	MillisNow = millis();
    
    ... snippage ...
    
    	if ((MillisNow - MillisThen) > UPDATEMS) {
    
    		TogglePin(PIN_HEARTBEAT);
    		tft.fillCircle(315,235,4,(word)MillisNow);			// colorful LCD heartbeat
    
    		MillisThen = MillisNow;
    	}
    }
    

    millis() produces an obvious counting sequence of colors. If that matters, you use random(0x10000).

    A square might be slightly faster than a circle. If that matters, you need an actual measurement in place of an opinion.

    Not much, but it makes me happy…

    There’s an obvious extension for decimal values: five adjacent spots in the resistor color code show you an unsigned number. Use dark gray for black to prevent it from getting lost; light gray and white would be fine. Prefix it with a weird color spot for the negative sign, should you need such a thing.

    Hexadecimal values present a challenge. That’s insufficient justification to bring back octal notation.

    In this day and age, color-coded numeric readouts should be patentable, as casual searching didn’t turn up anything similar. You saw it here first… [grin]

    Now that I think about it, a set of tiny buttons that control various modes might be in order.

  • APRS Turn Slope Units

    There’s a fundamental error in my writeup about setting the APRS Smart Beaconing parameters for the bike trackers: I blundered the units of Turn Slope.

    Rich Painter recently explained how that works:

    I ran across your blog on Smart Beaconing and saw something that needed correction.

    You state the Turn Slope is in units Degrees / MPH

    This is incorrect. Although the term Turn Slope is not a real slope (such as rise/run classically) that is what the originators used albeit incorrectly. They do however correctly attribute the units to MPH * Degrees (a product and hence not really a slope).

    In their formula they calculate a turn threshold as:
    turn_threshold = min_turn_angle + turn_slope / speed

    Looking at the units we see:
    = Degrees + (MPH * Degrees) / MPH

    which yields
    = Degrees + Degrees

    Which makes sense. It is too bad that the originators used the wrong term of Turn Slope which confuses most people. A better term would have been Turn Product.

    In looking back over that post, I have no idea where or how I got the wrong units, other than by the plain reading of the “variable name”.

    As he explained in a followup note:

    As for units… I was introduced to making unit balance way back in 1967-1968 science class in HS by a really fine science teacher. It has served me all my life and I’m thankful for that training.

    I have ever since told that teacher so!

    A while back, our Larval Engineer rammed an engineering physics class head-on and sent me a meme image, observing that I’d trained her well: if the units don’t work out, then you’re doing it wrong.

    Yes, yes, I do care about the units:

    Give a shit about the units
    Give a shit about the units
  • Bad Batteries Are Bad: Cold Weather Edition

    So we took an out-and-back walk across the Walkway Over the Hudson, after which I spotted this amusing sight:

    Parking Meter - empty battery box
    Parking Meter – empty battery box

    The horrible color balance comes from using a preset tuned for the M2’s new LED lights, rather than letting the camera figure things out on its own, then fighting it down after cropping.

    Anyhow, we did a bit over two miles of walking with outdoor temperature just over freezing. The camera lives in the left cargo pocket of my pants and the spare NB-5L battery in the camera case faces outward. Neither battery would power the camera at ambient temperature; evidently, being that cold reduced their output voltage below the level that the camera would accept.

    With a cold battery, the camera grunted, displayed a message about replacing the battery, and promptly shut itself off. Warming one of the batteries boosted its terminal voltage enough to take the picture, which accounts for not getting the proper color balance: I was fully occupied just getting the camera working.

    Back home and warmed up, the camera said both batteries were fully charged. They came from the BNF27 lot that produced low terminal voltages, so I’ll reserve them for warmer weather and use the BNI13 lot during the next few months.

     

  • Pilot InstaBoost: Battery Capacity

    The cardboard package liner claims the lithium-ion battery inside our Larval Engineer’s shiny new InstaBoost jump starter is good for 10.8 A·h and and the minuscule inscription on the case truncates it to 10 A·h. Given what I’ve seen for other batteries, either value would be true when measured under the most favorable conditions, but these curves still came as a bit of a surprise (clicky for more dots):

    Pilot Instaboost
    Pilot Instaboost

    The three short, abruptly dropping curves come from the main terminals, with the battery clamps attached to similar clamps (with a glitch when they shifted position) plugged into my CBA II/IV battery tester, showing that the InstaBoost shuts off after a few minutes, regardless of load. That makes good sense: don’t connect a lithium battery to a lead-acid battery for more than a few minutes!

    The two longer curves come from the 12 V jack on the side and show that it will run until the battery goes flat. Evidently, the internal battery protection circuit cuts out at less than the 10 V minimum I used for these tests.

    I didn’t bother testing the USB charging outlet, as I assume it would produce 5 V at 1 A for slightly less than twice as long.

    Under the most favorable conditions I could come up with, the actual battery capacity of 3.5 A·h is a third of what it should be. I’d expect that from the usual eBay supplier, not Lowe’s.

    Given the cheapnified clamps, perhaps Pilot deliberately gutted the battery capacity to save a few bucks. After all, the customers will never notice. Will they?

    Except…

    Another customer took his apart and found three 3.6 A·h “high output” (whatever that means) lithium cells in series. In that configuration, the individual cell capacity does not add and the pack should produce about 3.6 A·h. Those curves show it produces slightly less than that when discharged to 10 V, which means the thing works exactly like you’d expect. Indeed, it’s better than a typical second-tier product and much better than typical eBay crap.

    The most charitable explanation would be that somebody screwed up, multiplied the number of cells by their individual capacity, put that number in the specs, and everyone downstream ran with it. If the cells were in parallel, then the total capacity in ampere·hours would equal the sum of the cell capacity.

    If you change the specs to match the as-built hardware, then, apart from those cheapnified clamps, it’s working just fine…

  • Rounded Cable Clips

    This isn’t quite the smoothly rounded clip I had in mind:

    LED Cable Clip - rounded channel
    LED Cable Clip – rounded channel

    It seems somewhat better looking than the square design, though:

    LED Cable Clips
    LED Cable Clips

    I ran off a few of both styles to have some on hand:

    Cable clips - on platform
    Cable clips – on platform

    They’re in a bag until I install the new LED strips and needle light.

    The OpenSCAD source code:

    // LED Cable Clips
    // Ed Nisley - KE4ZNU - October 2014
    
    Layout = "Oval";			// Oval Square Build
    
    //- Extrusion parameters must match reality!
    
    ThreadThick = 0.20;
    ThreadWidth = 0.40;
    
    HoleWindage = 0.2;			// extra clearance
    
    Protrusion = 0.1;			// make holes end cleanly
    
    AlignPinOD = 1.70;			// assembly alignment pins: filament dia
    
    function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
    
    //----------------------
    // Dimensions
    
    Base = [12.0,12.0,IntegerMultiple(2.0,ThreadThick)];	// base over sticky square
    
    CableOD = 2.0;
    
    BendRadius = 3.0;
    
    Bollard = [BendRadius,(sqrt(2)*Base[0]/2 - CableOD - BendRadius),2*CableOD];
    B_BOT = 0;
    B_TOP = 1;
    B_LEN = 2;
    
    NumSides = (Shape == "Square") ? 5*4 : 6*3;
    
    //----------------------
    // Useful routines
    
    module PolyCyl(Dia,Height,ForceSides=0) {			// based on nophead's polyholes
    
      Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
    
      FixDia = Dia / cos(180/Sides);
    
      cylinder(r=(FixDia + HoleWindage)/2,
               h=Height,
               $fn=Sides);
    }
    
    module ShowPegGrid(Space = 10.0,Size = 1.0) {
    
      RangeX = floor(100 / Space);
      RangeY = floor(125 / Space);
    
    	for (x=[-RangeX:RangeX])
    	  for (y=[-RangeY:RangeY])
    		translate([x*Space,y*Space,Size/2])
    		  %cube(Size,center=true);
    
    }
    
    //-- Square clip with central bollard
    
    module SquareBollard() {
    
    	intersection() {
    		translate([0,0,(Base[2] + Bollard[B_LEN])/2])			// overall XYZ outline
    			cube(Base + [0,0,Bollard[2]],center=true);
    
    		union() {
    			translate([0,0,Base[2]/2])						// oversize mount base
    				scale([2,2,1])
    					cube(Base,center=true);
    
    			for (i=[-1,1] , j=[-1,1]) {						// corner bollards
    				translate([i*Base[0]/2,j*Base[1]/2,(Base[2] - Protrusion)])
    					rotate(180/NumSides)
    					cylinder(r=Bollard[B_BOT],h=(Bollard[B_LEN] + Protrusion),center=false,$fn=NumSides);
    
    			translate([0,0,(Base[2] - Protrusion)])			// center tapered bollard
    				cylinder(r1=Bollard[B_BOT],r2=Bollard[B_TOP],
    						 h=(Bollard[B_LEN] + Protrusion),
    						 center=false,$fn=NumSides);
    			}
    		}
    	}
    
    }
    
    //-- Oval clip with central passage
    
    module OvalPass() {
    
    	intersection() {
    		translate([0,0,(Base[2] + Bollard[B_LEN])/2])		// overall XYZ outline
    			cube(Base + [0,0,2*CableOD],center=true);
    
    		union() {
    			translate([0,0,Base[2]/2])						// oversize mount base
    				scale([2,2,1])
    					cube(Base,center=true);
    
    			for (j=[-1,1])									// bending ovals
    				translate([0,j*Base[1]/2,(Base[2] - Protrusion)])
    					resize([Base[0]/0.75,0,0])
    						cylinder(d1=0.75*(Base[1]-CableOD),d2=(Base[1]-CableOD)/cos(180/NumSides),
    								h=(Bollard[B_LEN] + Protrusion),
    								center=false,$fn=NumSides);
    		}
    	}
    /*
    #	translate([0,0,6])
    		rotate([0,90,0])
    			cylinder(d=CableOD,h=10,center=true,$fn=48);
    */
    }
    
    //----------------------
    // Build it
    
    ShowPegGrid();
    
    if (Layout == "Square")
    	SquareBollard();
    
    if (Layout == "Oval")
    	OvalPass();
    
  • DC-DC Boost Converter: Another QC FAIL

    Each LED emitter in the Kenmore 158 endcap light contains six chips in series:

    LED mount - lighting test
    LED mount – lighting test

    Even though the current has the usual exponential relationship to the terminal voltage, the slope at 200 mA (100 mA each, assuming they share & share alike) remains low enough that I (think I) can get away with just dialing in a voltage and leaving it at that; changes due to small temperature variations won’t cause meaningful differences in the current.

    That’s easier than building an adjustable current regulator, anyway.

    The heap disgorged two cheap DC-to-DC boost converters from halfway around the planet, with about the right specs:

    • 10 to 32 V DC in
    • 12 to 35 V out
    • 10 A
    • 150 W

    They couldn’t produce their rated output, but a pair of LEDs shouldn’t pose much of a challenge.

    So I wired one up to the bench supply, set it for 12 V, turned it on, and wham it maxed out the supply at 3 A with no load on the converter’s output.

    Huh.

    Adding a suitable load resistor brought the input current down, but the voltage adjustment trimpot didn’t have much effect and the bench supply would still wham hit 3 A with no provocation, so the load resistor didn’t actually make any difference. Eventually, I figured out that simply pressing my finger on the trimpot caused the output to vary wildly.

    Given that fairly broad hint, this became obvious:

    Boost Converter - trimpot pins
    Boost Converter – trimpot pins

    Evidently, I had used the other converter for the previous tests. Huh.

    With that trimpot pin soldered in place, the converter worked fine. Eyeballometrically speaking, the LEDs seem bright enough at 100 mA total (50 mA each) for my purposes, which happens at 18-ish V. Dissipating only 2 W won’t require nearly as much heatsink as they’re presently mounted on, although I should wait for warmer weather before concluding that they’re doing OK while crammed inside the end cap.

    Before declaring victory, I took a closer look at the board and found this mmm oversight:

    Boost Converter - masked 78L09 tab
    Boost Converter – masked 78L09 tab

    Notice the big pad under the 78L09 regulator, with six thermal vias to an expansive copper pour on the other side of the board, completely covered with red solder mask.

    Removing the regulator show the regulator’s footprint didn’t include the tab:

    Boost Converter - 78L09 footprint
    Boost Converter – 78L09 footprint

    Maybe they decided, after a careful analysis, that the regulator couldn’t possibly dissipate enough power to warrant the additional solder required for the entire thermal pad. Heck, pocket a fraction of a yuan on ten million boards and you’re livin’ large.

    Scraping the mask off, fluxing everything in sight, and soldering the regulator down probably won’t make any difference:

    Boost Converter - scraped and soldered
    Boost Converter – scraped and soldered

    Yes, The Bigger The Blob, The Better The Job strikes again. It does make me feel better and that’s all that counts.