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.
Mary wanted an opening in the front of the Darning Foot I didn’t modify the last time around, so I grabbed it in a machinist’s vise, grabbed that in the bench vise, and freehanded a Dremel slitting saw:
A bit of file work and it looks pretty good, although neither of us like the blurred-from-the-factory red lines:
This one retains the pin that lifts it as the needle rises, so it’s a hopping foot.
[Edit: Welcome Hackaday! You might prefer real vacuum tubes; searching for “vacuum tube leds” will turn up more posts about this long-running project. And, yes, I lit up a tube, just for old time’s sake, and have some plans for that huge triode.]
A single (knockoff) Neopixel hovers over a defunct halogen bulb:
The Arduino code comes from stripping down the Hard Drive Platter Mood Light to suit just one Neopixel, with the maximum PWM values favoring the red-blue-purple end of the color wheel:
Pixels[RED].Prime = 3;
Pixels[GREEN].Prime = 5;
Pixels[BLUE].Prime = 7;
printf("Primes: (%d,%d,%d)\r\n",Pixels[RED].Prime,Pixels[GREEN].Prime,Pixels[BLUE].Prime);
Pixels[RED].MaxPWM = 255;
Pixels[GREEN].MaxPWM = 64;
Pixels[BLUE].MaxPWM = 255;
Unlike the Mood Light’s dozen Neopixels jammed into the platter’s hub ring, running one Neopixel at full throttle atop the tube doesn’t overheat the poor controller. In a 22 °C room, PWM 255 white raises the cap’s interior temperature to 35 °C, which looks like a horrific 40 °C/W thermal coefficient if you figure the dissipation at 300 mW = 5 V x 60 mA.
Feeding those parameters into the raised sine wave equation causes the cap to tick along at 27 °C for an average dissipation of 120 mW, which sounds about right:
113 mW = 5 V x (20 + 20 + 5 mA) / 2
The effect is striking in a dark room, but it’s hard to photograph; the halogen capsule inside the bulb resembles a Steampunk glass jellyfish:
That ceramic light socket should stand on a round base with room for the Arduino controller. I think powering it from a wall wart through a USB cable makes sense, with a USB-to-serial converter epoxied inside the box for reprogramming.
It looks pretty good, methinks, should you like that sort of thing.
The Arduino source code as a GitHub gist:
| // Neopixel mood lighting for vacuum tubes | |
| // Ed Nisley – KE4ANU – January 2016 | |
| #include <Adafruit_NeoPixel.h> | |
| //———- | |
| // Pin assignments | |
| const byte PIN_NEO = 6; // DO – data out to first Neopixel | |
| const byte PIN_HEARTBEAT = 13; // DO – Arduino LED | |
| //———- | |
| // Constants | |
| #define UPDATEINTERVAL 25ul | |
| const unsigned long UpdateMS = UPDATEINTERVAL – 1ul; // update LEDs only this many ms apart minus loop() overhead | |
| // number of steps per cycle, before applying prime factors | |
| #define RESOLUTION 100 | |
| // want to randomize the startup a little? | |
| #define RANDOMIZE true | |
| //———- | |
| // Globals | |
| // instantiate the Neopixel buffer array | |
| Adafruit_NeoPixel strip = Adafruit_NeoPixel(1, PIN_NEO, NEO_GRB + NEO_KHZ800); | |
| uint32_t FullWhite = strip.Color(255,255,255); | |
| uint32_t FullOff = strip.Color(0,0,0); | |
| struct pixcolor_t { | |
| byte Prime; | |
| unsigned int NumSteps; | |
| unsigned int Step; | |
| float StepSize; | |
| byte MaxPWM; | |
| }; | |
| unsigned int PlatterSteps; | |
| // colors in each LED | |
| enum pixcolors {RED, GREEN, BLUE, PIXELSIZE}; | |
| struct pixcolor_t Pixels[PIXELSIZE]; // all the data for each pixel color intensity | |
| unsigned long MillisNow; | |
| unsigned long MillisThen; | |
| //– Figure PWM based on current state | |
| byte StepColor(byte Color, float Phi) { | |
| byte Value; | |
| Value = (Pixels[Color].MaxPWM / 2.0) * (1.0 + sin(Pixels[Color].Step * Pixels[Color].StepSize + Phi)); | |
| // Value = (Value) ? Value : Pixels[Color].MaxPWM; // flash at dimmest points | |
| return Value; | |
| } | |
| //– Helper routine for printf() | |
| int s_putc(char c, FILE *t) { | |
| Serial.write(c); | |
| } | |
| //—————— | |
| // Set the mood | |
| void setup() { | |
| pinMode(PIN_HEARTBEAT,OUTPUT); | |
| digitalWrite(PIN_HEARTBEAT,LOW); // show we arrived | |
| Serial.begin(57600); | |
| fdevopen(&s_putc,0); // set up serial output for printf() | |
| printf("Vacuum Tube Mood Light with Neopixels\r\nEd Nisley – KE4ZNU – January 2016\r\n"); | |
| /// set up Neopixels | |
| strip.begin(); | |
| strip.show(); | |
| // lamp test: a brilliant white dot | |
| printf("Lamp test: flash white\r\n"); | |
| for (byte i=0; i<3 ; i++) { | |
| for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with white | |
| strip.setPixelColor(j,FullWhite); | |
| } | |
| strip.show(); | |
| delay(500); | |
| for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with black | |
| strip.setPixelColor(j,FullOff); | |
| } | |
| strip.show(); | |
| delay(500); | |
| } | |
| // set up the color generators | |
| MillisNow = MillisThen = millis(); | |
| if (RANDOMIZE) | |
| randomSeed(MillisNow + analogRead(7)); | |
| else | |
| printf("Start not randomized\r\n"); | |
| printf("First random number: %ld\r\n",random(10)); | |
| Pixels[RED].Prime = 3; | |
| Pixels[GREEN].Prime = 5; | |
| Pixels[BLUE].Prime = 7; | |
| printf("Primes: (%d,%d,%d)\r\n",Pixels[RED].Prime,Pixels[GREEN].Prime,Pixels[BLUE].Prime); | |
| Pixels[RED].MaxPWM = 255; | |
| Pixels[GREEN].MaxPWM = 64; | |
| Pixels[BLUE].MaxPWM = 255; | |
| for (byte c=0; c < PIXELSIZE; c++) { | |
| Pixels[c].NumSteps = RESOLUTION * (unsigned int) Pixels[c].Prime; | |
| Pixels[c].Step = (RANDOMIZE) ? random(Pixels[c].NumSteps) : (3*Pixels[c].NumSteps)/4; | |
| Pixels[c].StepSize = TWO_PI / Pixels[c].NumSteps; // in radians per step | |
| printf("c: %d Steps: %d Init: %d",c,Pixels[c].NumSteps,Pixels[c].Step); | |
| printf(" PWM: %d\r\n",Pixels[c].MaxPWM); | |
| } | |
| } | |
| //—————— | |
| // Run the mood | |
| void loop() { | |
| MillisNow = millis(); | |
| if ((MillisNow – MillisThen) > UpdateMS) { | |
| digitalWrite(PIN_HEARTBEAT,HIGH); | |
| for (byte c=0; c < PIXELSIZE; c++) { // step to next increment in each color | |
| if (++Pixels[c].Step >= Pixels[c].NumSteps) { | |
| Pixels[c].Step = 0; | |
| printf("Cycle %d steps %d at %8ld delta %ld ms\r\n",c,Pixels[c].NumSteps,MillisNow,(MillisNow – MillisThen)); | |
| } | |
| } | |
| byte Value[PIXELSIZE]; | |
| for (byte c=0; c < PIXELSIZE; c++) { // … for each color | |
| Value[c] = StepColor(c,0.0); // figure new PWM value | |
| // Value[c] = (c == RED && Value[c] == 0) ? Pixels[c].MaxPWM : Value[c]; // flash highlight for tracking | |
| } | |
| uint32_t UniColor = strip.Color(Value[RED],Value[GREEN],Value[BLUE]); | |
| for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with color | |
| strip.setPixelColor(j,UniColor); | |
| } | |
| strip.show(); | |
| MillisThen = MillisNow; | |
| digitalWrite(PIN_HEARTBEAT,LOW); | |
| } | |
| } |
Lighting up that old voltage regulator tube conclusively demonstrated there’s no point in conjuring high voltages in this day & age. Nay, verily, merely lighting the filament of some tubes would require more power than seems reasonable.
A 1B3GT high-voltage regulator tube in the Box o’ Hollow State Electronics suggested a different approach:
With only a slight loss of historical accuracy, one could light the tube from the top with a Neopixel LED tucked into a similar cap, with power-and-data arriving through a suitably antiqued flying lead. That won’t work on tubes like that 1B3GT with an actual plate terminal at the top, nor with small Noval / miniature 7-pin tubes topped with an evacuation tip, but it’s fine for tubes like this 6SN7GTB:
Obviously, you want a relatively small cap atop the tube, lest the LED visually overwhelm the tube. Some preliminary tests (a.k.a. screwing around) showed that the mica spacer holding the dual triode elements together lights up wonderfully well and diffuses the glow throughout the tube.
Adafruit has relatively large round (and smaller roundish) Neopixel breakout boards, but I bought a bunch of knockoff Neopixels mounted on a 10 mm circular PCB from the usual eBay supplier:
Some PET braid tucked into a snippet of brass tubing dresses up a length of what might once have been audio cable. The braid wants to fray on the ends; confining it with heatstink or brass tubing is mandatory.
That’s a 1 µF ceramic SMD cap soldered between the +5 V and Gnd traces, atop a snippet of Kapton tape, in the hopes that it will help the 100 nF cap (on the other side of the board) tamp down the voltage dunks from PWM current pulses through that long thin wire. The leads come off toward the center to bend neatly upward into the cap.
Duplicating that old plate cap on the 1B3GT would be a fool’s errand, so I went full frontal Vader:
The interior recesses the LED far enough to allow for the tube’s top curvature, with a conical adapter to the smaller wiring channel that allows for more plastic supporting the brass tube:
A glob of epoxy inside the cap anchors the PCB and fuses all the loose ends / floppy wires / braid strands into a solid block that will never come apart again.
It should be printed (or primered and painted) with opaque black or maybe Bakelite Brown, but right now I have cyan PETG and want to see how it plays, soooo:
The cap floats in mid-air over a defunct Philips 60 W halogen bulb that I’ve been saving for just such an occasion. Obviously, you must epoxy / glue the cap in place for a permanent display.
The OpenSCAD source code as a Github gist:
| // Vacuum Tube LED Lights | |
| // Ed Nisley KE4ZNU January 2016 | |
| Layout = "Cap"; // Show Build Cap Box Octal Noval Mini7 | |
| Section = true; // cross-section the object | |
| //- Extrusion parameters must match reality! | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //———————- | |
| // Dimensions | |
| // https://en.wikipedia.org/wiki/Tube_socket#Summary_of_Base_Details | |
| T_NAME = 0; | |
| T_NUMPINS = 1; // Socket specifications | |
| T_PINCIRC = 2; | |
| T_PINDIA = 3; | |
| T_SOCKDIA = 4; | |
| TubeBase = [ | |
| ["Mini7", 8, 9.53, 1.016, 19.0], | |
| ["Octal", 8, 17.45, 2.36, 33.0], | |
| ["Noval",10, 11.89, 1.1016,20.5], | |
| ]; | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| Pixel = [7.0,10.0,3.0]; // ID = contact patch, OD = PCB dia, LENGTH = overall thickness | |
| //———————- | |
| // 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, | |
| $fn=Sides); | |
| } | |
| //———————- | |
| // Tube cap | |
| CapTube = [4.0,3/16 * inch,10.0]; // brass tube for flying lead to cap LED | |
| CapSize = [Pixel[ID],(Pixel[OD] + 3.0),(CapTube[OD] + 2*Pixel[LENGTH])]; | |
| CapSides = 6*4; | |
| module Cap() { | |
| difference() { | |
| union() { | |
| cylinder(d=CapSize[OD],h=(CapSize[LENGTH]),$fn=CapSides); // main cap body | |
| translate([0,0,CapSize[LENGTH]]) // rounded top | |
| scale([1.0,1.0,0.65]) | |
| sphere(d=CapSize[OD]/cos(180/CapSides),$fn=CapSides); // cos() fixes slight undersize vs cylinder | |
| cylinder(d1=(CapSize[OD] + 2*3*ThreadWidth),d2=CapSize[OD],h=1.5*Pixel[LENGTH],$fn=CapSides); // skirt | |
| } | |
| translate([0,0,-Protrusion]) // bore for wiring to LED | |
| PolyCyl(CapSize[ID],(CapSize[LENGTH] + 3*ThreadThick + Protrusion),CapSides); | |
| translate([0,0,-Protrusion]) // PCB recess with clearance for tube dome | |
| PolyCyl(Pixel[OD],(1.5*Pixel[LENGTH] + Protrusion),CapSides); | |
| translate([0,0,(1.5*Pixel[LENGTH] – Protrusion)]) // step + cone to retain PCB | |
| cylinder(d1=(Pixel[OD]/cos(180/CapSides)),d2=Pixel[ID],h=(Pixel[LENGTH] + Protrusion),$fn=CapSides); | |
| translate([0,0,(CapSize[LENGTH] – CapTube[OD]/(2*cos(180/8)))]) // hole for brass tube holding wire loom | |
| rotate([90,0,0]) rotate(180/8) | |
| PolyCyl(CapTube[OD],CapSize[OD],8); | |
| } | |
| } | |
| //———————- | |
| // Build it | |
| if (Layout == "Cap") { | |
| if (Section) | |
| difference() { | |
| Cap(); | |
| translate([-CapSize[OD],0,CapSize[LENGTH]]) | |
| cube([2*CapSize[OD],2*CapSize[OD],3*CapSize[LENGTH]],center=true); | |
| } | |
| else | |
| Cap(); | |
| } | |
| if (Layout == "Build") { | |
| Cap(); | |
| Spigot(); | |
| } |
I’ll be giving an in-depth talk about my adventures restoring that old HP 7475A plotter for the Poughkeepsie ACM Chapter at Marist College this evening:
This being the Association for Computing Machinery, I will talk a bit about the Superformula that makes it all possible:
The presentation will look a lot like this: ACM – Plotting Like Its 1989. The PDF doesn’t include my patter, but perhaps the linky love on each screen can fill in the details.
If you’re following along, the Python source code running on the plotter as a GitHub Gist:
| from chiplotle import * | |
| from math import * | |
| from datetime import * | |
| from time import * | |
| from types import * | |
| import random | |
| def superformula_polar(a, b, m, n1, n2, n3, phi): | |
| ''' Computes the position of the point on a | |
| superformula curve. | |
| Superformula has first been proposed by Johan Gielis | |
| and is a generalization of superellipse. | |
| see: http://en.wikipedia.org/wiki/Superformula | |
| Tweaked to return polar coordinates | |
| ''' | |
| t1 = cos(m * phi / 4.0) / a | |
| t1 = abs(t1) | |
| t1 = pow(t1, n2) | |
| t2 = sin(m * phi / 4.0) / b | |
| t2 = abs(t2) | |
| t2 = pow(t2, n3) | |
| t3 = -1 / float(n1) | |
| r = pow(t1 + t2, t3) | |
| if abs(r) == 0: | |
| return (0, 0) | |
| else: | |
| # return (r * cos(phi), r * sin(phi)) | |
| return (r, phi) | |
| def supershape(width, height, m, n1, n2, n3, | |
| point_count=10 * 1000, percentage=1.0, a=1.0, b=1.0, travel=None): | |
| '''Supershape, generated using the superformula first proposed | |
| by Johan Gielis. | |
| – `points_count` is the total number of points to compute. | |
| – `travel` is the length of the outline drawn in radians. | |
| 3.1416 * 2 is a complete cycle. | |
| ''' | |
| travel = travel or (10 * 2 * pi) | |
| # compute points… | |
| phis = [i * travel / point_count | |
| for i in range(1 + int(point_count * percentage))] | |
| points = [superformula_polar(a, b, m, n1, n2, n3, x) for x in phis] | |
| # scale and transpose… | |
| path = [] | |
| for r, a in points: | |
| x = width * r * cos(a) | |
| y = height * r * sin(a) | |
| path.append(Coordinate(x, y)) | |
| return Path(path) | |
| # RUN DEMO CODE | |
| if __name__ == '__main__': | |
| override = False | |
| plt = instantiate_plotters()[0] | |
| # plt.write('IN;') | |
| if plt.margins.soft.width < 11000: # A=10365 B=16640 | |
| maxplotx = (plt.margins.soft.width / 2) – 100 | |
| maxploty = (plt.margins.soft.height / 2) – 150 | |
| legendx = maxplotx – 2900 | |
| legendy = -(maxploty – 750) | |
| tscale = 0.45 | |
| numpens = 4 | |
| # prime/10 = number of spikes | |
| m_values = [n / 10.0 for n in [11, 13, 17, 19, 23]] | |
| # ring-ness 0.1 to 2.0, higher is larger | |
| n1_values = [ | |
| n / 100.0 for n in range(55, 75, 2) + range(80, 120, 5) + range(120, 200, 10)] | |
| else: | |
| maxplotx = plt.margins.soft.width / 2 | |
| maxploty = plt.margins.soft.height / 2 | |
| legendx = maxplotx – 3000 | |
| legendy = -(maxploty – 900) | |
| tscale = 0.45 | |
| numpens = 6 | |
| m_values = [n / 10.0 for n in [11, 13, 17, 19, 23, 29, 31, | |
| 37, 41, 43, 47, 53, 59]] # prime/10 = number of spikes | |
| # ring-ness 0.1 to 2.0, higher is larger | |
| n1_values = [ | |
| n / 100.0 for n in range(15, 75, 2) + range(80, 120, 5) + range(120, 200, 10)] | |
| print " Max: ({},{})".format(maxplotx, maxploty) | |
| # spiky-ness 0.1 to 2.0, higher is spiky-er (mostly) | |
| n2_values = [ | |
| n / 100.0 for n in range(10, 60, 2) + range(65, 100, 5) + range(110, 200, 10)] | |
| plt.write(chr(27) + '.H200:') # set hardware handshake block size | |
| plt.set_origin_center() | |
| # scale based on B size characters | |
| plt.write(hpgl.SI(tscale * 0.285, tscale * 0.375)) | |
| # slow speed for those abrupt spikes | |
| plt.write(hpgl.VS(10)) | |
| while True: | |
| # standard loadout has pen 1 = fine black | |
| plt.write(hpgl.PA([(legendx, legendy)])) | |
| pen = 1 | |
| plt.select_pen(pen) | |
| plt.write(hpgl.PA([(legendx, legendy)])) | |
| plt.write(hpgl.LB("Started " + str(datetime.today()))) | |
| if override: | |
| m = 4.1 | |
| n1_list = [1.15, 0.90, 0.25, 0.59, 0.51, 0.23] | |
| n2_list = [0.70, 0.58, 0.32, 0.28, 0.56, 0.26] | |
| else: | |
| m = random.choice(m_values) | |
| n1_list = random.sample(n1_values, numpens) | |
| n2_list = random.sample(n2_values, numpens) | |
| pen = 1 | |
| for n1, n2 in zip(n1_list, n2_list): | |
| n3 = n2 | |
| print "{0} – m: {1:.1f}, n1: {2:.2f}, n2=n3: {3:.2f}".format(pen, m, n1, n2) | |
| plt.select_pen(pen) | |
| plt.write(hpgl.PA([(legendx, legendy – 100 * pen)])) | |
| plt.write( | |
| hpgl.LB("Pen {0}: m={1:.1f} n1={2:.2f} n2=n3={3:.2f}".format(pen, m, n1, n2))) | |
| e = supershape(maxplotx, maxploty, m, n1, n2, n3) | |
| plt.write(e) | |
| pen = pen + 1 if (pen % numpens) else 1 | |
| pen = 1 | |
| plt.select_pen(pen) | |
| plt.write(hpgl.PA([(legendx, legendy – 100 * (numpens + 1))])) | |
| plt.write(hpgl.LB("Ended " + str(datetime.today()))) | |
| plt.write(hpgl.PA([(legendx, legendy – 100 * (numpens + 2))])) | |
| plt.write(hpgl.LB("More at https://softsolder.com/?s=7475a")) | |
| plt.select_pen(0) | |
| plt.write(hpgl.PA([(-maxplotx,maxploty)])) | |
| print "Waiting for plotter… ignore timeout errors!" | |
| sleep(40) | |
| while NoneType is type(plt.status): | |
| sleep(5) | |
| print "Load more paper, then …" | |
| print " … Press ENTER on the plotter to continue" | |
| plt.clear_digitizer() | |
| plt.digitize_point() | |
| plotstatus = plt.status | |
| while (NoneType is type(plotstatus)) or (0 == int(plotstatus) & 0x04): | |
| plotstatus = plt.status | |
| print "Digitized: " + str(plt.digitized_point) | |
A cold snap in early January caught plenty of humidity inside the house and, in fact, the attic temperature dropped so abruptly that the nails protruding through the roof iced over:
You’d think they were coated with plastic:
The incandescent bulb lighting the attic highlights the crystal planes:
As nearly as I can tell, the ice sublimes or melts-and-evaporates, because the plywood floor under the nails doesn’t have the drip marks you’d expect.
Just like all those EULAs we click through without reading, nobody pays any attention to the Customs declarations on packages:
The pick-and-place strip across the top contains ten U.FL connectors, a few of which might make their way onto the Ham It Up board. They cost a grand total of $2.09 (not the $12.00 shown on the label) delivered halfway around the planet in a bit over two weeks.
I confess: I just couldn’t pass up some new fashion accessories…
The SMA-to-N cables arrived unexpectedly early, so I fired up the spectrum analyzer to see how the Ham It Up Upconverter behaved at 60 kHz (think WWVB), a smidge below its 100 kHz minimum input frequency spec. It’s worth noting that you can’t do a frequency sweep of the 100 kHz to 50 MHz upconverter response using the tracking generator, because the output sits 125 MHz above the input; yes, it took me a while to dope that out…
Anyhow, the 60 kHz sine wave from the (sub-audio-frequency up to 2 MHz, 600 Ω -ish output) signal generator, passed through a 5X attenuator, and terminated in 50 Ω:
It emerges from the H-I-U in Passthrough mode 3.6 dB lower:
In Upconvert mode, the output sits 14 dB below the Passthrough output and 17.6 below the input:
At that span setting, I don’t trust the frequency resolution of that 125.0605 MHz marker readout.
Cranking the signal generator to produce -10 dBm at the H-I-U output in Passthrough mode brings up a bunch of harmonics:
In Upconvert, they’re down 13.9 dB from the Passthrough output:
The H-I-U should have about 10 dB conversion loss at 100 kHz, so losing another 4 dB beyond the thing’s rated low end isn’t entirely surprising.
All in all, it works fine…
The Smell of Molten Projects in the Morning 