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Saddest Arduino Demo

The Adafruit 2.8 inch TFT Touch Shield for Arduino v2 seems just about ideal for a small control panel, such as one might use with a modified sewing machine. All you need is a few on-screen buttons, a few status display, and a bit of Arduino love: what more could one ask?

So I gimmicked up some small buttons with GIMP, made two large buttons with ImageMagick, and lashed together some Arduino code based on the Adafruit demo:

Adafruit TFT display - timing demo

Adafruit TFT display – timing demo

The picture doesn’t do justice to the display: it’s a nice piece of hardware that produces a crisp image. The moire patterns come from the interaction of TFT display pixels / camera pixels / image resizing.

It’s not obvious from the Adafruit description, but the display is inherently portrait-mode as shown. The (0,0) origin lies in the upper left corner, just over the DC power jack, and screen buffer updates proceed left-to-right, top-to-bottom from there.

The gotcha: even with the Arduino Mega’s hardware SPI, writing the full display requires nearly 4 seconds. Yeah, slow-scan TV in action.  Writing the screen with a solid color requires several seconds.

After commenting out the serial tracing instructions from the Adafruit demo and tweaking a few other things, these timings apply:

Writing background
Elapsed: 3687
Writing six buttons
Elapsed: 529
Overwriting six buttons
Elapsed: 531
Rewriting buttons 10 times
Elapsed: 1767
Overwriting 2 large buttons
Elapsed: 1718

The timings work out to:

  • Background: 240×320 → 48 µs/pixel
  • Smaller buttons: 50×25 → 71 µs/pixel → 88 ms/button
  • Rewriting one button: 71 µs/pixel
  • Larger buttons: 120×64 → 56 µs/pixel → 430 ms/button

The button images come from BMP files on a MicroSD card and 8 KB of RAM won’t suffice for even a small button. Instead, the transfer loop buffers 20 pixels = 60 bytes from the card, writes them to the display, and iterates until it’s done.

Trust me on this: watching the buttons gradually change is depressing.

Yes, it could work as a control panel for the sewing machine, but it doesn’t have nearly the pep we’ve come to expect from touch-screen gadgetry. On the other paw, Arduinos are 8-bit microcontrollers teleported from the mid-90s, when crappy 20×4 LCD panels were pretty much as good as it got.

The SPI hardware clock runs at half the oscillator frequency = 16 MHz/2 = 8 MHz = 125 ns/bit. Clocking a single byte thus requires 1 µs; even allowing that each pixel = 3 bytes = 6 SPI operations, there’s a lot of software overhead ripe for the chopping block. I’d be sorely tempted to write a pair of unrolled loops that read 20 pixels and write 20 pixels with little more than a pointer increment & status spin between successive SPI transfers.

It’ll make hotshot C++ programmers flinch, but splicing all that into a single routine, throwing out all the clipping and error checking, and just getting it done might push the times down around 20 µs/pixel. Admittedly, that’s barely twice as fast, but should be less depressing.

However, even with all that effort, the time required to update the screen will clobber the motor control. You can’t devote a big fraction of a second to rewriting a button at the same time you’re monitoring the pedal position, measuring the motor speed, and updating the control voltage. That’s the same problem that makes Arduino microcontrollers inadequate for contemporary 3D printers: beyond a certain point, the hardware is fighting your efforts, not helping you get things done.

A reasonable workaround: no screen updates while the motor turns, because you shouldn’t have any hands free while you’re sewing.

There’s also no way to make up for not having enough RAM or video hardware. The same display runs full-speed video on a Raspberry Pi…

The Arduino source code, hacked from the Adafruit demo:

// 2.8 inch TFT display exercise
// Crudely hacked from Adafruit demo code: spitftbitmap.ino
// 2014-07-03 Ed Nisley KE4ZNU

  This is our Bitmap drawing example for the Adafruit ILI9341 Breakout and Shield

  Check out the links above for our tutorials and wiring diagrams
  These displays use SPI to communicate, 4 or 5 pins are required to
  interface (RST is optional)
  Adafruit invests time and resources providing this open source code,
  please support Adafruit and open-source hardware by purchasing
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.
  MIT license, all text above must be included in any redistribution

#include <Adafruit_GFX.h>    // Core graphics library
#include "Adafruit_ILI9341.h" // Hardware-specific library
#include <SPI.h>
#include <SD.h>

#define TFT_DC 9
#define TFT_CS 10
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC);

#define SD_CS 4

unsigned long MillisNow, MillisThen;

void setup(void) {


  Serial.print(F("Initializing SD card..."));
  if (!SD.begin(SD_CS)) {


void loop() {
  Serial.println(F("Writing background"));
  MillisThen = millis();

  bmpDraw("Test1.bmp", 0, 0);

  MillisNow = millis();
  Serial.print(F(" Elapsed: "));
  Serial.println(MillisNow - MillisThen);

  Serial.println(F("Writing 6 small buttons"));
  MillisThen = millis();



  MillisNow = millis();
  Serial.print(F(" Elapsed: "));
  Serial.println(MillisNow - MillisThen);

  Serial.println(F("Overwriting 6 small buttons"));
  MillisThen = millis();



  MillisNow = millis();
  Serial.print(F(" Elapsed: "));
  Serial.println(MillisNow - MillisThen);

  Serial.println(F("Writing small button 10x2 times"));
  MillisThen = millis();

  for (byte i=0; i<10; i++) {

  MillisNow = millis();
  Serial.print(F(" Elapsed: "));
  Serial.println(MillisNow - MillisThen);

  Serial.println(F("Overwriting 2 large buttons"));
  MillisThen = millis();  



  MillisNow = millis();
  Serial.print(F(" Elapsed: "));
  Serial.println(MillisNow - MillisThen);


// This function opens a Windows Bitmap (BMP) file and
// displays it at the given coordinates.  It's sped up
// by reading many pixels worth of data at a time
// (rather than pixel by pixel).  Increasing the buffer
// size takes more of the Arduino's precious RAM but
// makes loading a little faster.  20 pixels seems a
// good balance.

#define BUFFPIXEL 20

void bmpDraw(char *filename, uint8_t x, uint16_t y) {

  File     bmpFile;
  int      bmpWidth, bmpHeight;   // W+H in pixels
  uint8_t  bmpDepth;              // Bit depth (currently must be 24)
  uint32_t bmpImageoffset;        // Start of image data in file
  uint32_t rowSize;               // Not always = bmpWidth; may have padding
  uint8_t  sdbuffer[3*BUFFPIXEL]; // pixel buffer (R+G+B per pixel)
  uint8_t  buffidx = sizeof(sdbuffer); // Current position in sdbuffer
  boolean  goodBmp = false;       // Set to true on valid header parse
  boolean  flip    = true;        // BMP is stored bottom-to-top
  int      w, h, row, col;
  uint8_t  r, g, b;
  uint32_t pos = 0, startTime = millis();

  if((x >= tft.width()) || (y >= tft.height())) return;

//  Serial.println();
//  Serial.print(F("Loading image '"));
//  Serial.print(filename);
//  Serial.println('\'');

  // Open requested file on SD card
  if ((bmpFile = == NULL) {
//    Serial.print(F("File not found"));

  // Parse BMP header
  if(read16(bmpFile) == 0x4D42) { // BMP signature
//    Serial.print(F("File size: "));
//	Serial.println(read32(bmpFile));
    (void)read32(bmpFile); // Read & ignore creator bytes
    bmpImageoffset = read32(bmpFile); // Start of image data
//    Serial.print(F("Image Offset: ")); Serial.println(bmpImageoffset, DEC);
    // Read DIB header
//    Serial.print(F("Header size: "));
//	Serial.println(read32(bmpFile));
    bmpWidth  = read32(bmpFile);
    bmpHeight = read32(bmpFile);
    if(read16(bmpFile) == 1) { // # planes -- must be '1'
      bmpDepth = read16(bmpFile); // bits per pixel
//      Serial.print(F("Bit Depth: ")); Serial.println(bmpDepth);
      if((bmpDepth == 24) && (read32(bmpFile) == 0)) { // 0 = uncompressed

        goodBmp = true; // Supported BMP format -- proceed!
//        Serial.print(F("Image size: "));
//        Serial.print(bmpWidth);
//        Serial.print('x');
//        Serial.println(bmpHeight);

        // BMP rows are padded (if needed) to 4-byte boundary
        rowSize = (bmpWidth * 3 + 3) & ~3;

        // If bmpHeight is negative, image is in top-down order.
        // This is not canon but has been observed in the wild.
        if(bmpHeight < 0) {
          bmpHeight = -bmpHeight;
          flip      = false;

        // Crop area to be loaded
        w = bmpWidth;
        h = bmpHeight;
        if((x+w-1) >= tft.width())  w = tft.width()  - x;
        if((y+h-1) >= tft.height()) h = tft.height() - y;

        // Set TFT address window to clipped image bounds
        tft.setAddrWindow(x, y, x+w-1, y+h-1);

        for (row=0; row<h; row++) { // For each scanline...

          // Seek to start of scan line.  It might seem labor-
          // intensive to be doing this on every line, but this
          // method covers a lot of gritty details like cropping
          // and scanline padding.  Also, the seek only takes
          // place if the file position actually needs to change
          // (avoids a lot of cluster math in SD library).
          if(flip) // Bitmap is stored bottom-to-top order (normal BMP)
            pos = bmpImageoffset + (bmpHeight - 1 - row) * rowSize;
          else     // Bitmap is stored top-to-bottom
            pos = bmpImageoffset + row * rowSize;
          if(bmpFile.position() != pos) { // Need seek?
            buffidx = sizeof(sdbuffer); // Force buffer reload

          for (col=0; col<w; col++) { // For each pixel...
            // Time to read more pixel data?
            if (buffidx >= sizeof(sdbuffer)) { // Indeed
    , sizeof(sdbuffer));
              buffidx = 0; // Set index to beginning

            // Convert pixel from BMP to TFT format, push to display
            b = sdbuffer[buffidx++];
            g = sdbuffer[buffidx++];
            r = sdbuffer[buffidx++];
          } // end pixel
        } // end scanline
//        Serial.print(F("Loaded in "));
//        Serial.print(millis() - startTime);
//        Serial.println(" ms");
      } // end goodBmp

  if(!goodBmp) Serial.println(F("BMP format not recognized."));

// These read 16- and 32-bit types from the SD card file.
// BMP data is stored little-endian, Arduino is little-endian too.
// May need to reverse subscript order if porting elsewhere.

uint16_t read16(File &f) {
  uint16_t result;
  ((uint8_t *)&result)[0] =; // LSB
  ((uint8_t *)&result)[1] =; // MSB
  return result;

uint32_t read32(File &f) {
  uint32_t result;
  ((uint8_t *)&result)[0] =; // LSB
  ((uint8_t *)&result)[1] =;
  ((uint8_t *)&result)[2] =;
  ((uint8_t *)&result)[3] =; // MSB
  return result;
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Xubuntu: Setting Up a Solid State Drive

It turns out that the clever idea of moving the swap partition to a USB flash drive had no effect whatsoever; the UI continued to freeze up during OpenSCAD compiles and suchlike, with the drive activity light on solid and not much in the way of swap activity. Sooo, I wondered what would happen with the /tmp directory on non-rotating memory.

Then I spotted a sale on a Samsung 840 EVO 120 GB solid state drive, which seemed like it might improve almost everything in one swell foop. That’s a tiny drive, at least by contemporary standards, but all my data files live downstairs on the file server, so the desktop drive holds just the Xubuntu installation.

It’s worth noting that SSDs tend to fail suddenly and catastrophically, so that if the only copy of your data is on that drive, there is no recovery. In this case, I’d lose some configuration that changes with every installation, a few locally installed / compiled-from-source programs, and little else.

The nice thing about transferring a Linux installation: boot a live CD image (I used Ubuntu 14.04LTS, the same as the desktop box), copy the files to the new drive, set up Grub, and you’re back on the air. That recipe worked fine, although I used rsync -au to copy the files and then updated /etc/fstab with the SSD’s new UUID (rather than duplicate a supposedly unique ID).

The Grub recipe does require a bit of delicate surgery, so I removed the OEM hard drive and rebooted the live CD image before doing this. If the SSD fell victim to a finger fumble, I could just start over again:

sudo mount /dev/sda1 /mnt
for f in dev proc sys usr ; do sudo mount --bind /$f /mnt/$f ; done
sudo chroot /mnt
sudo update-grub
sudo grub-install /dev/sda
sudo grub-install --recheck /dev/sda
for f in dev proc sys usr ; do sudo umount /mnt/$f ; done
sudo umount /mnt

Then reboot from the SSD and It Just Worked.

Dropbox and DigiKam noticed the UUID change and asked for advice; there’s no need for re-registration, re-activation, or re-authorization.

The overall time from boot to login isn’t much shorter, because of the tedious delay while the network and the NFS shares to get up & running, but the desktop UI startup zips right along.

The same OpenSCAD compile that previously brought the UI to a halt has no effect, so I hereby declare victory. I think the complex solid models that used to take forever will see much the same speedup.

The Dell hard drive (an ordinary 7200 RPM 3.5 inch brick) lies abandoned in place under the fancy black shroud; the Optiplex 980 layout butts the drive’s right-angle SATA connectors hard against the CPU heatsink and offers no spare SATA power connectors. There was just enough room to wedge the SSD above the PCI connectors, where it won’t get into any trouble:

Samsung 840 EVO SSD in Optiplex 980

Samsung 840 EVO SSD in Optiplex 980

The hard drive contains the never-used Windows 7 partition and the corresponding recovery / diagnostic partitions; keeping the drive with the Optiplex chassis seems like a Good Idea.

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Checkout Scanner Configuration

One of the price scanners at Stop & Shop was already lit up when I arrived:

Price Scanner - Baud Rate Selection

Price Scanner – Baud Rate Selection

Let’s take a closer look:

Price Scanner - Baud Rate Selection - detail

Price Scanner – Baud Rate Selection – detail

Can it be that S&S, having outsourced the scanning & bagging operations to its customers, now expects sysadmin skills?

Given our previous experience, I didn’t even think of fiddling with it…

And, yes, I know that “baud rate” is an oxymoron.

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Kenmore 158: Hall Effect Speed Control Pedal

The original foot pedal controlled the sewing machine’s AC motor speed with a carbon disk rheostat:

Rheostat with brass spacer button

Rheostat with brass spacer button

Given the troubles we’ve had with that thing, using it as an input device isn’t going to happen.

More modern “digital” sewing machines seem to use linear potentiometers or analog optical sensors; retrofitting that old housing seems difficult, at best, because the actuator has barely 15 mm of travel. I’m sure somebody could conjure up a bell crank to amplify the mechanical motion, but that ain’t me.

This doodle shows the rudiments of an alternative:

Hall effect distance sensor - original doodle

Hall effect distance sensor – original doodle

The general idea is to have the existing cross bar / roller move a magnet relative to an analog Hall effect sensor: closer to sensor = higher magnetic field = higher sensor output voltage. Ideally, the magnet provides enough field to max out the sensor just before the pedal reaches the limit of its travel, so the magnet never quite touches the sensor.

An optical wedge would serve a similar function, but this pretty much eliminates all the critical alignment & focusing & friction issues. Plus, I have a bunch of analog Hall effect sensors

I have a stock of telescoping brass tubing, so the inner tube slides over the 4 mm screw that threads into the existing hardware, replacing the old shaft. That tube slides inside an outer tube that’s aligned in a block attached to the pedal frame; an epoxy blob holds it in position. The inner tube should have a nut on the left end to allow adjusting the rest position.

The Hall effect sensors have a zero-field bias at about VCC/2, so a smaller opposing (and fixed) bias magnet on the far side of the sensor pushes the output voltage to the lower limit. The adjusting screw on that side sets the bias level, if that’s needed.

A spring that’s not shown pushes the cross bar away from the block holding the outer tube and sensor; that’s what restores the magnet to its rest position when the pedal is up.

This being the age of rapid prototyping:

Foot Control Sensor Mount - solid model - top

Foot Control Sensor Mount – solid model – top

The bottom view shows an opening for the epoxy blob halfway between the rear wall and the opening for the magnet and Hall effect sensor:

Foot Control Sensor Mount - solid model - bottom

Foot Control Sensor Mount – solid model – bottom

Two bosses inside the pedal base fit into those rectangular cutouts, with the centerline of the tubing at the top of the bosses.

The inner brass tube holds the outer tube in the proper alignment while the epoxy slab cures:

Kenmore 158 - Hall speed control - tubing fit

Kenmore 158 – Hall speed control – tubing fit

Fortunately, two of the neodymium magnets in my collection worked out perfectly as the main and bias magnets. The smaller bias magnet just barely saturates the output when epoxied to the back of the sensor and the larger magnet has about 15 mm of active range.

The assembly sequence required half a dozen separate epoxy applications; I used quick-curing clear epoxy, rather than my usual JB Weld, because this isn’t the place for a steel filled epoxy. The final step put a washer on the back of the inner tube to hold the spring in place, with the Hall effect sensor invisible under the wad of closed-cell foam at the bottom:

Kenmore 158 - Hall speed control - epoxy curing

Kenmore 158 – Hall speed control – epoxy curing

The spring comes from the Big Box o’ Medium Springs, which contains a few more just like it.

That solid model and the OpenSCAD code below include several refinements that don’t appear in the photos. In particular, the graceful slope on the top front will look a whole lot better than the abrasive adjustment required to fit the chunky first version into the pedal case:

Kenmore 158 - Hall speed control - prototype interior

Kenmore 158 – Hall speed control – prototype interior

On the other paw, that’s what rapid prototyping is all about. I had no way to measure that dimension, but building one to figure it worked pretty well.

Things that may / will need tweaking:

  • The centerline of the tubing lies on the same plane as the tops of the bosses under those three screws, but the bosses are not particularly flat. Perhaps some setscrews to fine-tune the height and front-to-back tilt angle?
  • The sketch had adjustable magnet positions; the as-built hardware doesn’t. It’s not clear they’re needed, although that depends on having exactly the right magnets.
  • The screws are #4 sheet metal and fit nicely into the metric holes; the original screws held a thin aluminum bracket in place, not that chunky block. I could recess the heads, but …
  • A 3D printed clamp holding the cable and strain relief bushing in place would be cuter than the sheet metal strap I bashed from scrap.

The far end of the cable terminates in a 6-pin mini-DIN connector, left over from the days when PCs (remember PCs?) had PS/2 mice & keyboards:

Kenmore 158 Improved Speed Control Pedal - cable wiring diagram

Kenmore 158 Improved Speed Control Pedal – cable wiring diagram

I’ll eventually put the emitter resistor into the circuit; these sensors work fine without it. The cable provides electrostatic shielding and I’m hoping the impedance is low enough that the motor won’t induce any noise. In any event, some low-pass filtering won’t slow down the response enough to notice.

Next, some measurements…

The OpenSCAD source code:

// Foot Control Sensor Mount
// Ed Nisley - KE4ZNU - June 2014

Layout = "Show";			// Plate Build Show 

//- Extrusion parameters must match reality!
//  Print with 4 shells and 3 solid layers

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
// Origin at center front edge of plate
//  Z = bottom surface

PlateSize = [85.0,53.0,15.0];						// overall plate size
MidZ = PlateSize[2]/2;								//  height of spring midline
PlateCornerRadius = 1.5;

FrontBevel = [0.0,15.0,5.5];						// Y from front, Z from centerline

ScrewHolesOC = [[-75.0/2,(37.0 - 14.0/2)],[-75.0/2,(37.0 + 14.0/2)],[75.0/2,37.0]];
ScrewHoleDia = 4.0;									// allow alignment slop around 3 mm / #4 screws

BossSize = [[12.0,28.0],[12.0,27.0]];				// mounting bosses: L R
BossOC = [[-75.0/2,37.0],[75.0/2,37.0]];

Stroke = 15.0;										// foot pedal actuation distance

Bushing = [5.6,23.0];								// outer brass tube
MainMagnet = [10.0,5.0];							// magnet on pushrod
BiasMagnet = [5.0,2.0];								// bias magnet behind Hall effect sensor
Spring = [9.0,8.0];									// recess for pushrod retracting spring
Washer = [10.0,1.0];								// recess for washer atop pushrod

OD = 0;												// subscripts for cylindrical objects
LEN = 1;

SensorThick = 2.0;									// Hall effect sensor on bias magnet
FilletLength = 0.75;								// glue fillet on main magnet

// 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,

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])


// Basic plate shape

module Plate() {

R = PlateCornerRadius;
Px = PlateSize[0]/2 - R;
Py = PlateSize[1] - R;
Sides = 4*4;

BevelAngle = atan2((MidZ - FrontBevel[2]),FrontBevel[1]);

echo("Bevel angle: ",BevelAngle);

	difference() {
		linear_extrude(height = PlateSize[2]) {
			hull() {
				translate([-(20-R),R])			// avoid left front boss
				translate([-Px,20+R])			// avoid left front boss

		translate([0,0,-Protrusion])						// screw bosses
			linear_extrude(height = (MidZ + Protrusion),convexity=2)
				for (i=[0:1])

		translate([0,0,-Protrusion])						// plate mounting screws
			linear_extrude(height = 2*PlateSize[2] + Protrusion,convexity=3)
				for (i=[0:2])

		translate([0,0,MidZ + FrontBevel[2]])		// Front bevel


// Modify plate for position sensor hardware

module Sensor() {

GluePort = [1.5*Bushing[OD],Bushing[OD]/2,PlateSize[2]];	// port for glue anchor around bushing

MagnetPort = [1.5*MainMagnet[OD],
			  (Stroke + MainMagnet[LEN] + FilletLength + SensorThick),
			  (PlateSize[2] + 2*Protrusion)];

	difference() {

		translate([0,(PlateSize[1] - Bushing[LEN] - Protrusion),MidZ])		// bushing

		translate([-GluePort[0]/2,										// bushing anchor opening
				  (PlateSize[1] - 0.66*Bushing[LEN] - GluePort[1]/2),
				  MidZ - GluePort[2] + Bushing[OD]/2])

		translate([0,(PlateSize[1] - Bushing[LEN] - MagnetPort[1]/2),MagnetPort[2]/2 - Protrusion])

		translate([0,(PlateSize[1] - Bushing[LEN] - MagnetPort[1] + Protrusion),MidZ])
				PolyCyl(BiasMagnet[OD],BiasMagnet[LEN] + Protrusion,6);

		translate([0,(PlateSize[1] + Protrusion),MidZ])
			rotate([90,0,0]) rotate(180/8)
				PolyCyl(Spring[OD],Spring[LEN] + Protrusion,8);

		translate([0,(PlateSize[1] + Protrusion),MidZ])
			rotate([90,0,0]) rotate(180/8)
				PolyCyl(Washer[OD],Washer[LEN] + Protrusion,8);



if (Layout == "Plate") {

if (Layout == "Show")

if (Layout == "Build") {


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Tweaked Crossword Scanning

In what’s surely a change intended to better meet the needs of their customers, the newspaper changed the crossword layout just a little teeny bit, so my previous script needed a tweak:

echo Scanning...
scanimage --mode Gray --opt_emulategray=yes --resolution 300 -l 5 -t 0 -x 105 -y 195 --format=pnm > /tmp/scan.pnm
echo Converting...
convert /tmp/scan.pnm -level 45%,60% -resize 2400x3150 +repage -unsharp 0 /tmp/trim.png
convert -density 300 -size 2550x3300 canvas:white /tmp/trim.png -gravity center -composite /tmp/page.pdf
echo Printing...
lp -n 2 /tmp/page.pdf
echo Done!

It now spits out two large-print copies, to better meet their actual needs, at least for two of their customers.



Monthly Science: Springtime Ground Temperatures

The last month’s ground temperatures:

Temperatures - Garden Patio Water

Temperatures – Garden Patio Water

The “Garden” trace comes from a waterproof Hobo datalogger buried a few inches underground, beneath a thick layer of chipped leaf mulch. The “Patio” trace comes from the center of the cramped space below the concrete patio, buried flush with the bare dirt floor. The “Water” trace is the temperature at the incoming water pipe from the town water main, which passes 150 feet under the front yard.

Calculated eyeballometrically, the temperature rose 7 °F in about a month.

The datalogger in the garden came from the “cold cellar” veggie storage buckets, so I don’t have a year-long record. On the other paw, it looks like the patio temperature will be a pretty good proxy for the minimum garden temperature.

I hand-cleaned the Hobo CSV files and fed the results into a Gnuplot script that’s replete with the cruft of ages:

#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
echo Output file: ${ofile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "Ground Temperatures"
set key noautotitles right center
unset mouse
set bmargin 4
set grid xtics ytics
set timefmt "%m/%d/%Y %H:%M:%S"
set xdata time
set xlabel "Date"
set format x "%Y-%m-%d"
set xrange [:"07/15/2014"]
set xtics font "arial,12"
#set mxtics 2
#set logscale y
#set ytics nomirror autofreq
set ylabel "Temperature - F"
#set format y "%4.0f"
#set yrange [30:90]
#set mytics 2
#set y2label "right side variable"
#set y2tics nomirror autofreq 2
#set format y2 "%3.0f"
#set y2range [0:200]
#set y2tics 32
#set rmargin 9
set datafile separator ","
#set label 1 "Garden"     at "05/31/2014",25 left font "arialbd,10" tc lt 3
#set arrow from 2.100,110 to 2.105,103 lt 1 lw 2 lc 0
plot	\
    "Garden.csv" using 2:3 with lines lt 3 lw 1 title "Garden",\
    "Patio.csv"  using 2:3 with lines lt 2 lw 1 title "Patio",\
    "Water.csv"  using 2:5 with lines lt 4 lw 1 title "Water",\


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Kenmore 158: NEMA 23 Motor Adapter

After removing the AC motor from the sewing machine, I wondered if a NEMA 23 stepper motor would fit:

Kenmore 158 - NEMA 23 stepper - trial fit

Kenmore 158 – NEMA 23 stepper – trial fit

Huh. Who’d’a thunk it? That’s just too good to pass up…

Although you wouldn’t use PLA for the real motor mount, this was easy:

Drive Motor Mount - solid model

Drive Motor Mount – solid model

And the whole affair fits pretty much like you’d expect:

Kenmore 158 - NEMA 23 stepper - on adapter

Kenmore 158 – NEMA 23 stepper – on adapter

The NEMA 23 motor doesn’t have the same end profile as the AC motor and the adapter plate gets in the way of the pulley, but flipping the pulley end-for-end perfectly aligned the belt.

For whatever it’s worth, here’s how I removed the pressed-on gear from the shaft:

NEMA 23 Stepper - removing gear

NEMA 23 Stepper – removing gear

I’m pretty sure I have a little gear puller somewhere, but it’s not where I expected to find it, which means it could be anywhere.

Much to my astonishment, the shafts on both motors are exactly 1/4″ inch. I filed a flat on the shaft to avoid having the setscrew goober the poor thing.

A stepper isn’t the right hammer for this job, because it can’t possibly reach 8000 rpm, but it’ll be good enough to explore the parameter space and weed out the truly stupid mistakes. A brushless DC motor from halfway around the planet would fit in the same spot.

The OpenSCAD source code:

// NEMA 23 Stepper Mounting Plate
// Ed Nisley - KE4ZNU - June 2014

Layout = "Build";			// Build Show 

//- Extrusion parameters must match reality!
//  Print with 4 shells and 3 solid layers

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

inch = 25.4;

function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

// Dimensions
// Origin at bottom front corner of plate as mounted on machine
//	motor mounted on rear surface, so recess is on that side

PlateThick = 4.0;				// overall plate thickness

SlotOffset = [10.0,13.0,0];		// center nearest origin, motor in X+,Y+ direction
SlotSize = [8.0,25.0];			// diameter of mounting screw , overall end-to-end length

CutoutOffset = [0.0,40.0,0];	// cutout around machine casting
CutoutSize = [18.0,18.0];

MotorBase = 58.0;				// square base plate side
MotorHoleOC = 47.2;				// hole center-to-center spacing
MotorHoleOffset = MotorHoleOC/2;
MotorHoleDia = 5.0;
MotorBaseCornerRadius = (MotorBase - MotorHoleOC)/2;

FlangeWidth = 20.0;				// mounting flange

MotorCenter = [(FlangeWidth + MotorBase/2),(MotorBase/2),0];		// XY of shaft centerline

MotorShaftDia = 7.0;			// allow some clearance

HubDia = 38.5;					// allow some clearance
HubHeight = 1.8;

// 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,

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])


// Build it!

module BasePlate() {

	difference() {
//		cube([(MotorCenter[0] + MotorBase/2),MotorBase,PlateThick],center=false);
		linear_extrude(height = PlateThick) {
			hull() {
				translate([MotorBaseCornerRadius,MotorBase - MotorBaseCornerRadius])
				translate([FlangeWidth + MotorBase - MotorBaseCornerRadius,MotorBase - MotorBaseCornerRadius])
				translate([FlangeWidth + MotorBase - MotorBaseCornerRadius,MotorBaseCornerRadius])

		translate(MotorCenter - [0,0,Protrusion]) {
				PolyCyl(MotorShaftDia,(PlateThick + 2*Protrusion),8);		// shaft hole
			PolyCyl(HubDia,(HubHeight + Protrusion));						// hub recess
			for (x=[-1,1] , y=[-1,1]) {
						PolyCyl(MotorHoleDia,(PlateThick + 2*Protrusion),8);

		translate(SlotOffset - [0,0,Protrusion]) {							// adjustment slot
			linear_extrude(height = (PlateThick + 2*Protrusion))
				hull() {
					translate([0,(SlotSize[1] - SlotSize[0])])


		translate(CutoutOffset - [Protrusion,0,Protrusion])
			linear_extrude(height = (PlateThick + 2*Protrusion))
				square(CutoutSize + [Protrusion,Protrusion]);


if (Layout == "Show") {

if (Layout == "Build") {
	translate([-(SlotOffset[0] + MotorBase/2),MotorBase/2,PlateThick])