Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Well, that fix didn’t take long to fail; they sure don’t make ’em like they used to:
OEM Replacement fan in freezer
The “new” fan’s bearing failure sounded more like an owl than a dog, but it was certainly not what we wanted to hear in the middle of the night. A replacement fan costs on the order of $60, which seems like an absurdly high number for what’s basically a clock motor, a plastic fan blade, and some stamped steel.
After mulling the situation for a bit, I concluded that the refrigerator has reached that age where stuffing more money into it doesn’t make much sense: the compressor will drop dead in fairly short order. It’s time for a gonzo fix that also slightly reduces the clutter in the Basement Laboratory Warehouse: stick a PC case fan and wall wart into the freezer, ignore their temperature ratings, and see what happens.
A polycarbonate sheet, a band saw, some step drills, a big hole saw, and an hour of Quality Shop Time produced a perfectly serviceable space transformer to mate the fan to the airflow director:
PC case fan in air flow director
The plate surrounds the squishy foam washers from the OEM motor mount, with the fan on its own rubbery posts: there won’t be any vibration transmitted to the plastic air flow director! The obligatory Kapton tape on the right holds a closed-cell foam wrap around the wires to prevent rattling; I’d done much the same when I tore the thing apart after the first OEM fan failure.
The air flow is toward you out of the screen: the fan draws air from the refrigerator compartment through the evaporator coils, then directly into a square duct that leads back to the refrigerator. Whatever doesn’t make it into the duct flows into the freezer compartment through the row of vents at the top of the picture.
I assume some serious modeling went into choosing the OEM fan blade configuration and spacing so as to optimize the distribution. I hope just moving some air in roughly the right direction will suffice; I have no way to measure any interesting numbers, so this is entirely cut-and-try.
The PC case fan expects 12 VDC, which comes from a standard wall wart conspicuously labeled “For Indoor Use Only”. Well, this is certainly indoor, even if it’s not quite what they expected. The wart plugs into a cobbled-together extension cord receptacle with male 1/4 inch quick-disconnect tabs that match the female QD connectors on the OEM wiring harness that originally plugged into the fan:
PC case fan with adapted wall wart
All that fits into the space behind the rear panel, with the wart wrapped in a sheet of closed-cell foam to prevent rattling and provide a bit of protection:
PC case fan installed in freezer
The rear panel covers the mess, exposing only the row of vent holes along the top. The air flow is upward through the evaporator coil and fins, through the fan, and back to the two compartments.
One question remains: will the fan continue to start below 0 °F (-20 °C)?
Given the ball bearings in the fan, it ought to remain quiet, but I’ve thought that before. Now, however, I have a generous supply of case fans and wall warts that plug into the mechanical and power adapters, so I can replace fans for a long time.
The latch is about the same as before, but the top endplate now has two cable ports and locating pins to take the force from the battery contact springs:
HT-GPS Case – latch detail
The bottom endplate has a hole for the TinyTrak3 Mode switch, plus two locating pins that hold the plate in place:
HT-GPS Case – Wouxun KG-UV3D base view
A detail shot of the two endplates shows the new holes:
HT-GPS Case – endplate detail
Snippets of brass rod became locating pins, each slipped into a hole atop a dab of epoxy to lock it in place:
HT-GPS Case – locating pin detail
The boards slide in pretty much the way you’d expect:
HT-GPS Case – Trial fit – rear view
The OpenSCAD code punches a third cable hole in the case for the HT wiring. I had high hopes that it would fit through the endplate, but …
Seen from the other end, there’s not much to see. The next case will have a slightly narrower LED opening:
HT-GPS Case – Trial fit – base view
The imperfection running down the side comes from a brief pause in the proceedings while the support plate fell out of the opening. As a consequence, I discovered that the LED window doesn’t need any support at all.
This view shows one of the battery contacts peeking through the hole for a yet-to-be-made stud:
HT-GPS Case – Wouxun KG-UV3D rear view
The solid model show some additional revisions, but it’s pretty close to the green plastic versions:
HT-GPS Case – holes and pins – solid model
The OpenSCAD source code:
// Wouxun KB-UV3D Battery Pack Case
// Ed Nisley KE4ZNU April 2012
include </home/ed/Thing-O-Matic/lib/MCAD/units.scad>
include </home/ed/Thing-O-Matic/Useful Sizes.scad>
// Layout options
Layout = "Fit";
// Overall layout: Fit Show
// Printing plates: Build1 .. Buildn (see bottom!)
// Parts: TT3 Audio DSub Shell Base Top
// Shapes: RadioBase Contact
// Speaker-mic mount: PlugPlate
ShowGap = 20; // spacing between parts in Show layout
//- Extrusion parameters must match reality!
// Print with +1 shells and 3 solid layers
ThreadThick = 0.25;
ThreadWidth = 2.0 * ThreadThick;
HoleWindage = 0.2;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
Protrusion = 0.1; // make holes end cleanly
//----------------------
//- Dimensions
CaseOverallHeight = 31.5; // from battery surface, must clear PCBs!
CaseOverallWidth = 56;
CaseOverallLength = 80.25; // inside of base to end of compartment
BatteryClearance = 1.5; // contact seal height = air gap to compartment
// Interface to radio battery contacts
// Length = shell length
// calculated after everything else, so as to fill the compartment
PlateWidthMin = 53.0;
PlateWidthMax = 54.5;
PlateThick = IntegerMultiple(2.0,ThreadThick);
PlateAngle = atan(PlateThick/(PlateWidthMax/2 - PlateWidthMin/2));
ContactDia = 7.0; // use rounded contact for simplicity
ContactRecess = IntegerMultiple(0.5,ThreadThick); // recess for contact plate
ContactGapX = 10.5; // X space between contacts
Contact1Y = 52.5; // offset from base to edge of contact
Contact2Y = 56.5;
ContactStudDia = Clear4_40;
ContactStudHead = Head4_40;
ContactStudHeadThick = Head4_40Thick;
// Offsets from battery surface to PCB centerlines
// TT3 must be above HT back shell for DB9 clearance
// These must cooperate with the numbers in the case shell module
TT3Offset = 17.5 + PlateThick;
AudioOffset = 4.0 + PlateThick;
// Plate interface to base alignment holes and notches
BaseWidthInner = PlateWidthMin;
BaseWidthOuter = CaseOverallWidth;
BaseLength = CaseOverallHeight; // perpendicular to battery surface
BaseThick = IntegerMultiple(1.0,ThreadThick); // minimum sheet thickness below teeth
BaseWidthTaper = 5.0; // ramp across entire width
BaseOpeningMax = 43.0;
BaseOpeningMin = 33.0;
BaseOpeningY = 5.3;
BaseOpeningDepth = IntegerMultiple(2.25,ThreadThick);
BaseTotalThick = BaseThick + BaseOpeningDepth;
echo("Base min thick: ",BaseThick," total: " ,BaseTotalThick);
BaseTabWidth = 6.0;
BaseTabThick = 2.0;
BaseTabGap = 7.0;
BaseTabOC = BaseTabWidth + BaseTabGap;
BaseToothSection = 3*BaseTabWidth + 2*BaseTabGap;
BaseToothBase = 5.8;
BaseToothTip = 2.8;
BaseToothThick = 2.0;
BaseToothAngle = atan(BaseOpeningDepth/0.6);
BaseToothOC = BaseTabOC;
WedgeAngle = atan(BaseWidthTaper/((BaseWidthOuter - BaseWidthInner)/2));
BaseEndLip = ThreadThick; // should be 0.25 mm or so
BaseEndWidth = (PlateWidthMin - 3*BaseToothBase - 2*BaseToothTip)/2;
BaseEndAngle = atan((BaseOpeningDepth - BaseEndLip)/BaseOpeningY);
SwitchBody = [8.6,3.7,3.3]; // mode switch
// Plate interface to HT battery latch, cables, and connectors
TopThick = IntegerMultiple(5.5,ThreadThick); // plate thickness for stiffness behind latch bar
echo("Top plate thick: ",TopThick);
DB9Recess = TopThick - 4.0; // recess to max TT3 PCB clearance behind DB9 plate
TabEngageLength = 1.6; // tab engaging surface length
TabWidth = 3.0; // ... width
TabEngageHeight = 4.5; // ... above battery compartment floor
TabHeight = 7.5; // tab ramp top above battery compartment floor
TabOC = 40.0;
LatchBarWidth = 3.4; // sliding latch mechanism (brass L stock)
LatchBarDepth = 3.4;
LatchBarThick = 0.35;
echo(" ... minimum: ",TopThick - LatchBarDepth);
SplitOffset = TT3Offset - 3.5;
TopBevel = 1.0; // bevel at top of battery compartment
TopBevelAngle = 45;
PinOffsetWidth = 2.5; // choose to center in sides of case shell
PinOffsetHeight = 12.0; // above baseplate bottom
PinDepth = 7.0; // into case shell
PinDia = 1.2;
ShellLength = CaseOverallLength - BaseThick - TopThick;
echo("Shell length: ",ShellLength);
// Speaker-mic plug plate
PlugBaseThick = 2.5; // recess depth
PlugFillThick = 3.0; // outer plate 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,
$fn=Sides);
}
module ShowPegGrid(Space = 10.0,Size = 1.0) {
Range = floor(50 / Space);
for (x=[-Range:Range])
for (y=[-Range:Range])
translate([x*Space,y*Space,Size/2])
%cube(Size,center=true);
}
//-------------------
// Component parts
//-----
// TinyTrak3+ PCB and component envelope
// Some dimensions should feed into the case shell, but don't
module TinyTrak3(Length = 1.0) {
PCBThick = 1.6;
PCBWide = 36.5;
TopHigh = 9.5;
TopWide = PCBWide - 1.5;
BotHigh = 2.5;
BotWide = 35.0;
PCBx = PCBWide/2;
PCBy = (PCBThick + HoleWindage)/2;
URx = TopWide/2;
URy = PCBy + TopHigh;
LRx = BotWide/2;
LRy = PCBy + BotHigh;
linear_extrude(height=Length,center=false,convexity=2) {
polygon(points=[[URx,URy],[URx,PCBy],[PCBx,PCBy],[PCBx,-PCBy],[LRx,-PCBy],[LRx,-LRy],
[-LRx,-LRy],[-LRx,-PCBy],[-PCBx,-PCBy],[-PCBx,PCBy],[-URx,PCBy],[-URx,URy]
]);
}
}
//-----
// Interface PCB and component envelope
// Some dimensions should feed into the case shell, but don't
module AudioInterface(Length = 1.0) {
PCBThick = 2.0;
PCBWide = 49.5;
TopHigh = 9.0 + Protrusion;
TopWide = 46.0;
BotHigh = 3.0;
BotWide = 44.0;
PCBx = PCBWide/2;
PCBy = (PCBThick + HoleWindage)/2;
URx = TopWide/2;
URy = PCBy + TopHigh;
LRx = BotWide/2;
LRy = PCBy + BotHigh;
linear_extrude(height=Length,center=false,convexity=2) {
polygon(points=[[URx,URy],[URx,PCBy],[PCBx,PCBy],[PCBx,-PCBy],[LRx,-PCBy],[LRx,-LRy],
[-LRx,-LRy],[-LRx,-PCBy],[-PCBx,-PCBy],[-PCBx,PCBy],[-URx,PCBy],[-URx,URy]
]);
}
}
//-----
// DB-9 (DE-9) panel opening
// http://www.interfacebus.com/Connector_D-Sub_Mechanical_Dimensions.html
// DB-9 shell mounts on outside surface of case
// This is for the solder terminal side
module DSubMin9(Length = 1.0) {
Holex = 0.984/2 * inch;
HoleDia = Tap4_40;
URx = 0.769/2 * inch;
URy = 0.432/2 * inch;
linear_extrude(height=Length,center=false,convexity=3) {
polygon(points=[[URx,URy],[URx,-URy],[-URx,-URy],[-URx,URy]]);
for (x = [-1,1]) {
translate([x*Holex,0,0])
rotate(45) circle(r=(HoleDia + HoleWindage)/2,$fn=4);
}
}
}
//-----
// Central case shape
// This *should* depend directly on the circuit board sizes, but doesn't
// The "Offset" parameters attempt to bottle up all the board sizes
// Support in LED window must be hand-fit to work correctly... and isn't needed!
module CaseShell(Length=(ShellLength),Holes="true") {
// Polygon coordinates are in XY plane
URx = 40.0/2;
URy = CaseOverallHeight;
MRx = CaseOverallWidth/2;
MRy = 15.0;
LRx = CaseOverallWidth/2;
LRy = (LRx - PlateWidthMin/2)*tan(PlateAngle);
BRx = PlateWidthMax/2;
BRy = PlateThick - 0*Protrusion;
PRx = PlateWidthMin/2; // combined battery plate
PRy = 0;
ScrewOffset = 20.0; // from top end of case
LEDWindow = [30.0,5.0,6]; // with case aligned vertically
LEDOffset = [15,URy,(Length + TopThick - 25.0)];
TrimPot1 = [-14,TT3Offset,(Length + TopThick - 30)];
TrimPot2 = [-14,TT3Offset,(Length + TopThick - 37.5)];
HTCableDia = 3.2;
HTCableOffset = AudioOffset + HTCableDia/2 + 1.0;
rotate([90,0,180])
union() {
difference() {
linear_extrude(height=Length,center=false,convexity=5)
polygon(points=[[URx,URy],[MRx,MRy],[LRx,LRy],[BRx,BRy],[PRx,PRy],
[-PRx,PRy],[-BRx,BRy],[-LRx,LRy],[-MRx,MRy],[-URx,URy]]);
if (Holes) {
translate([0,AudioOffset,-Protrusion])
AudioInterface(Length + 2*Protrusion);
translate([0,TT3Offset,-Protrusion])
TinyTrak3(Length + 2*Protrusion);
for (y = [TT3Offset,AudioOffset])
translate([-CaseOverallWidth,y,(Length - ScrewOffset)])
rotate([0,90,0])
rotate(0) // Z rotation puts point upward for printing
PolyCyl(Tap4_40,CaseOverallWidth);
translate(LEDOffset)
rotate([90,90,0])
translate([-LEDWindow[0]/2,-LEDWindow[1]/2,-Protrusion])
cube(LEDWindow,center=false);
for (p = [TrimPot1,TrimPot2])
translate(p)
rotate([-90,90,0]) // Y rotation puts point upward for printing
PolyCyl(3.0,URy);
for (x=[-1,1]) {
translate([x*(CaseOverallWidth/2 - PinOffsetWidth),
PinOffsetHeight,
(Length - PinDepth)])
rotate(45) // align hole sides with case sides
PolyCyl(PinDia,2*TopThick);
translate([x*(CaseOverallWidth/2 - PinOffsetWidth),
PinOffsetHeight,
-PlateThick])
rotate(45) // align hole sides with case sides
PolyCyl(PinDia,(PlateThick + PinDepth));
}
translate([-(ContactGapX/2 + ContactDia/2),0,(Contact1Y + ContactDia/2)])
rotate([90,0,0])
Contact();
translate([+(ContactGapX/2 + ContactDia/2),0,(Contact2Y + ContactDia/2)])
rotate([90,0,0])
Contact();
translate([CaseOverallWidth/2,HTCableOffset,(Length - HTCableDia/2)])
rotate([0,90,0])
cube([(HTCableDia + Protrusion),HTCableDia,CaseOverallWidth],center=true);
}
}
if (false)
if (Holes)
translate(LEDOffset) // support plug in LED window
rotate([90,90,0])
translate([-0.95*LEDWindow[0]/2,-0.80*LEDWindow[1]/2,ThreadWidth/2])
cube([0.95*LEDWindow[0],0.80*LEDWindow[1],2*ThreadWidth],center=false);
}
}
//-----
// Battery contact recess
// This gets subtracted from the bottom plate in two places
// Align points to print upward
module Contact() {
if (true)
union() { // vertical printing with case
translate([0,0,-(ContactRecess + Protrusion)/2])
PolyCyl(ContactDia,(ContactRecess + Protrusion),8);
translate([0,0,-(PlateThick + Protrusion)])
rotate(60/2)
PolyCyl(ContactStudDia,PlateThick,6);
translate([0,0,-(ContactRecess + ContactStudHeadThick/3)])
PolyCyl(ContactStudHead,ContactStudHeadThick,8); // allow for solder blob
}
else
union() { // horizontal printing alone
translate([0,0,-(ContactRecess - Protrusion)/2])
PolyCyl(ContactDia,(ContactRecess + Protrusion),8);
translate([0,0,-(PlateThick + Protrusion)])
PolyCyl(ContactStudDia,(PlateThick + 2*Protrusion));
translate([0,0,-(ContactRecess + ContactStudHeadThick/3)])
PolyCyl(ContactStudHead,ContactStudHeadThick,8); // allow for solder blob
}
}
//-----
// Radio bottom locating feature
// This polygon gets subtracted from the battery pack base
module RadioBase() {
linear_extrude(height=(BaseOpeningDepth + Protrusion),center=false,convexity=5)
polygon(points=[
[-BaseOpeningMax/2,-Protrusion],
[-BaseOpeningMin/2,BaseOpeningY],
[-(BaseToothOC/2 + BaseToothBase/2),BaseOpeningY],
[-(BaseToothOC/2 + BaseToothTip/2),(BaseOpeningY - BaseToothThick)],
[-(BaseToothOC/2 - BaseToothTip/2),(BaseOpeningY - BaseToothThick)],
[-(BaseToothOC/2 - BaseToothBase/2),BaseOpeningY],
[ (BaseToothOC/2 - BaseToothBase/2),BaseOpeningY],
[ (BaseToothOC/2 - BaseToothTip/2),(BaseOpeningY - BaseToothThick)],
[ (BaseToothOC/2 + BaseToothTip/2),(BaseOpeningY - BaseToothThick)],
[ (BaseToothOC/2 + BaseToothBase/2),BaseOpeningY],
[ BaseOpeningMin/2,BaseOpeningY],
[ BaseOpeningMax/2,-Protrusion],
[ (BaseTabOC + BaseTabWidth/2),-Protrusion],
[ (BaseTabOC + BaseTabWidth/2),BaseTabThick],
[ (BaseTabOC - BaseTabWidth/2),BaseTabThick],
[ (BaseTabOC - BaseTabWidth/2),-Protrusion],
[ BaseTabWidth/2,-Protrusion],
[ BaseTabWidth/2,BaseTabThick],
[-BaseTabWidth/2,BaseTabThick],
[-BaseTabWidth/2,-Protrusion],
[-(BaseTabOC + BaseTabWidth/2),-Protrusion],
[-(BaseTabOC + BaseTabWidth/2),BaseTabThick],
[-(BaseTabOC - BaseTabWidth/2),BaseTabThick],
[-(BaseTabOC - BaseTabWidth/2),-Protrusion],
],
convexity=5
);
}
//-----
// Battery pack base
module Base() {
difference() {
rotate([-90,180,0])
CaseShell(BaseTotalThick,false);
translate([0,0,BaseThick])
RadioBase();
translate([-BaseWidthOuter,-(BaseThick + BaseEndLip)/tan(BaseEndAngle),0])
rotate([BaseEndAngle,0,0])
difference() {
cube([2*BaseWidthOuter,3*BaseOpeningY,BaseOpeningDepth],center=false);
translate([(BaseWidthOuter - (BaseToothSection + 2*Protrusion)/2),0,0])
cube([(BaseToothSection + 2*Protrusion),1.2*BaseOpeningY,BaseOpeningDepth],center=false);
}
translate([0,0,BaseThick])
rotate([(-90 + BaseToothAngle),0,0])
translate([0,-0.5,0])
cube([(BaseToothSection + 2*Protrusion),1.0,10],center=true);
for (x=[-1,1])
translate([x*(CaseOverallWidth/2 - PinOffsetWidth),PinOffsetHeight,-Protrusion])
rotate(45) // align hole side with plate side
PolyCyl(PinDia,2*TopThick);
translate([(-SwitchBody[0]/2),TT3Offset,-SwitchBody[2]/2])
scale([1,1,2])
cube(SwitchBody);
}
}
//-----
// Top plate with latch
// Split around TinyTrak3 serial connector
// ... which must be at the same height as in the shell!
// The cable hole sizes & locations are entirely ad-hoc
module TopPlate() {
Cable1Dia = 5.0;
Cable2Dia = 5.0;
CableHoleLength = TopThick + 2*Protrusion;
CableHoleZ = -Protrusion;
DB9Plate = [32.0,13.5,1.25]; // plate surrounding connector body
difference() {
rotate([-90,180,180])
CaseShell(TopThick,false);
translate([0,-TT3Offset,-Protrusion])
DSubMin9(TopThick + 2*Protrusion);
translate([0,-TT3Offset,(TopThick - DB9Plate[2]/2)])
cube([DB9Plate[0],DB9Plate[1],(DB9Plate[2] + Protrusion)],center=true);
translate([-CaseOverallWidth,-SplitOffset,-2*Protrusion]) // split the plate
cube([2*CaseOverallWidth,4*Protrusion,(TopThick + 2*Protrusion)]);
translate([0,0,(TopThick - TopBevel)])
rotate([-TopBevelAngle,0,0])
translate([-CaseOverallWidth,-TopThick,0])
cube([2*CaseOverallWidth,2*TopThick,2*TopThick],center=false);
for (x=[-1,1])
translate([(x*TabOC/2),
(-TabHeight/2 + Protrusion),
(TopThick - TabEngageLength/2 + Protrusion/2)])
rotate([90,0,0])
cube([TabWidth,
(TabEngageLength + Protrusion),
(TabHeight + Protrusion)],center=true);
translate([-CaseOverallWidth,
-(TabEngageHeight + LatchBarWidth - BatteryClearance),
(TopThick - LatchBarDepth)])
cube([2*CaseOverallWidth,(LatchBarWidth + LatchBarThick),(LatchBarDepth + Protrusion)]);
for (x=[-1,1])
translate([(x*CaseOverallWidth/4),
-(TabEngageHeight + LatchBarWidth + Clear2_56/2 - BatteryClearance + Protrusion),
0]) {
translate([0,0,-Protrusion])
rotate(45) // align sides with slot
PolyCyl(Tap2_56,(TopThick + 2*Protrusion));
translate([0,0,(TopThick - LatchBarDepth)])
rotate(60) // align sides with slot
PolyCyl((Head2_56 + Protrusion),TopThick,6); // extra extra clearance
}
for (x=[-1,1])
translate([x*(CaseOverallWidth/2 - PinOffsetWidth),-PinOffsetHeight,-Protrusion])
rotate(45) // align hole side with plate side
PolyCyl(PinDia,2*TopThick);
for (x=[-1,1]) // coincidentally line up with latch tabs
translate([(x*TabOC/2),-(SplitOffset - 3.0),-Protrusion])
scale([1,1.7,1])
PolyCyl(Cable1Dia,CableHoleLength,6);
}
}
//-----
// Speaker-Mic plug mounting plate
module PlugPlate() {
JackOC = 11.20; // 14.25 OD - (3.58 + 2.58)/2
JackScrewDia = 4.6;
JackScrewOffsetX = 1.00;
JackScrewOffsetY = 5.25; // mounting screw to edge of lower recess
PlugBaseWidth = 9.25; // lower section of plate
PlugBaseLength = 22.0;
PlugBaseRadius = 1.75;
Plug3Offset = 5.25; // edge of base recess to 3.5 mm jack
Plug2BezelDia = 7.1; // 2.5 mm plug
Plug2BezelThick = 1.04;
Plug2ScrewDia = 6.0;
Plug3ScrewLength = 3.0;
Plug3BezelDia = 8.13; // 3.5 mm plug
Plug3BezelThick = 1.6;
Plug3ScrewDia = 7.95;
Plug3ScrewLength = 4.0;
PlugFillOffsetX = JackScrewOffsetX - 0.5; // base recess CL to fill CL
PlugFillOffsetY = -10.5; // ... to edge of fill plate
PlugFillWidth = 11.0;
PlugFillLength = 34.00;
PlugFillRadius1 = 1.5;
PlugFillRadius2 = 4.5;
PlugFillOffsetYTotal = 0;
BaseX = PlugBaseWidth/2 - PlugBaseRadius;
BaseY = PlugBaseLength/2 - PlugBaseRadius;
difference() {
union() {
linear_extrude(height=PlugBaseThick,center=false,convexity=3)
hull() {
translate([-BaseX,-BaseY,0])
circle(r=PlugBaseRadius,$fn=8);
translate([-BaseX, BaseY,0])
circle(r=PlugBaseRadius,$fn=8);
translate([ BaseX, BaseY,0])
circle(r=PlugBaseRadius,$fn=8);
translate([ BaseX,-BaseY,0])
circle(r=PlugBaseRadius,$fn=8);
}
translate([PlugFillOffsetX,
(PlugFillLength/2 - PlugBaseLength/2 + PlugFillOffsetY),
PlugBaseThick])
linear_extrude(height=PlugFillThick,center=false,convexity=5)
hull() {
translate([0,-(PlugFillLength/2 - PlugFillRadius2),0])
circle(r=PlugFillRadius2,$fn=10);
translate([-(PlugFillWidth/2 - PlugFillRadius1),-PlugBaseLength/2,0])
circle(r=PlugFillRadius1,$fn=8);
translate([-(PlugFillWidth/2 - PlugFillRadius1),
(PlugFillLength/2 - PlugFillRadius1),0])
circle(r=PlugFillRadius1,$fn=8);
translate([(PlugFillWidth/2 - PlugFillRadius1),
(PlugFillLength/2 - PlugFillRadius1),0])
circle(r=PlugFillRadius1,$fn=8);
translate([(PlugFillWidth/2 - PlugFillRadius1),-PlugBaseLength/2,0])
circle(r=PlugFillRadius1,$fn=8);
}
}
translate([0,-JackOC/2,-Protrusion])
rotate(360/16) {
PolyCyl(Plug3BezelDia,(Plug3BezelThick + Protrusion),8);
PolyCyl(Plug3ScrewDia,(PlugBaseThick + PlugFillThick + 2*Protrusion),8);
}
translate([0,+JackOC/2,-Protrusion])
rotate(360/16) {
PolyCyl(Plug2BezelDia,(Plug2BezelThick + Protrusion),8);
PolyCyl(Plug2ScrewDia,(PlugBaseThick + PlugFillThick + 2*Protrusion),8);
}
translate([JackScrewOffsetX,-(PlugBaseLength/2 + JackScrewOffsetY),0])
PolyCyl(JackScrewDia,(PlugBaseThick + PlugFillThick + Protrusion));
}
}
//-------------------
// Build things...
ShowPegGrid();
if (Layout == "TT3")
TinyTrak3();
if (Layout == "Audio")
AudioInterface();
if (Layout == "DSub")
DSubMin9();
if (Layout == "Shell")
CaseShell(CaseOverallLength);
if (Layout == "Top")
TopPlate();
if (Layout == "Base")
Base();
if (Layout == "RadioBase")
RadioBase();
if (Layout == "PlugPlate")
PlugPlate();
if (Layout == "Contact")
rotate([180,0,0])
Contact();
if (Layout == "Show" || Layout == "Fit") {
translate([0,-ShellLength/2,0]) {
translate([0,(Layout == "Show")?-ShowGap:0,0])
rotate([90,0,0])
color("SandyBrown") Base();
translate([0,0,0])
color("Olive") render() CaseShell();
translate([-(CaseOverallWidth/2 + 10),50,CaseOverallHeight/2])
rotate([0,-90,0])
color("Brown") PlugPlate();
translate([0,((Layout == "Show")?(ShellLength + ShowGap):ShellLength),0])
rotate([-90,0,0])
color("Chocolate") TopPlate();
}
}
if (Layout == "Build1") {
translate([0,-CaseOverallHeight/2,ShellLength])
rotate([-90,0,0])
CaseShell();
}
if (Layout == "Build2") {
translate([5 + CaseOverallHeight,0,0])
rotate([0,0,90])
Base();
translate([-(5 + CaseOverallHeight),0,0])
rotate(90)
TopPlate();
}
if (Layout == "Build3") {
translate([0,0,(PlugBaseThick + PlugFillThick)])
rotate([180,0,0])
PlugPlate();
}
This panel-mount LED indicator glued to the Z-axis stage of my Thing-O-Matic had been dutifully showing a bright green glow when the extruder heater was active:
Failed LED panel indicator
Of late, it began flickering erratically whenever the heater turned on. It used to flicker when the PID loop (hacked to be a bang-bang controller) drove the extruder temperature past the switching threshold, but this was worse.
It’s rated for 5 VDC, 25 mA and has an internal resistor to make that happen. Channeling the true spirit of DIY 3D printer electronics, I deliberately connected it directly across the 12 V extruder power and let it burn at 80 mA. The poor thing was surprisingly bright for an ancient green LED ( the 8124 date code stamped on the side I pried off for the picture says it’s three decades old) and, even under that abuse, it lasted for a year: not to be sniffed at.
I’d expect the LED to fail open when a bond wire burned through, but you just never can tell. It worked fine on the bench, which is typical of all intermittent failures.
So I popped an identical indicator off the stack, conservatively added a 270 Ω series resistor to drop the excess voltage, and it’s all good again.
Unlike the previous kludge, this GPS interface case resembles an extrusion with the PCBs sliding into place, held by setscrews along the edges of the slots:
HT-GPS Adapter Case – end view
Those errant threads seem to arise from not quite bonding to the corner. The battery side of the case (bottom in this view) is one thread wide, which isn’t quite enough. Adding another thread makes it 1 mm wide, which seems excessive.
The idea was to glue the battery interface plate on that side, but printing the case vertically puts various flaws along that surface:
HT-GPS Adapter Case – bottom view
So the next iteration will merge the battery plate with the case and print the whole affair in one shot. This view shows all the parts separately:
HT-GPS Adapter Case – exploded bottom view
This shows the case joined with the battery plate, neatly aligned for printing:
HT-GPS Adapter Case – combined battery interface
The battery plate has a 0.1 mm extension into the case to avoid problems from objects with coincident planes. Unfortunately, however, that means the intersection between the base plate and the shell forms a line with three planes extending from it: the two outside walls (which are co-planar) and the plate extension inside the case. Skeinforge sometimes complains mightily about that, despite my having applied a union() to fuse the plate with the case: obviously I don’t quite understand how union() works.
I think the battery contact holes will come out close enough to being right; they all have points on the top edge to reduce the overhang problem.
One gotcha: the actual metallic contact studs for the battery. The contacts for the ICOM IC-Z1A case came from carefully shaped brass screws secured by nuts above the PCB and that’s what I’ve been designing around for this case. Unfortunately, the PCB must slide in before installing the studs, which means reaching into the depths of the case, with all the wiring in the way, to turn those nuts. Fortunately, the PCB has plenty of clearance in that direction, but … it’ll be awkward at best.
The studs also need a slot / socket / dingus to prevent rotation while tightening the nuts; right now the contact plate is circular-ish, but maybe I should rethink that.
Although I don’t often block-quote other sources, for this I’ll make an exception:
The Cassini Plasma Spectrometer (CAPS, off since June 2011) was powered back on on March 16 based on the unanimous agreement of the review board at the CAPS turn-on review held on March 8. All went as planned for both the instrument and the spacecraft during the turn-on. The high rail to chassis short internal to the instrument that was part of what prompted it to be turned off last June was not present, and no changes were seen in the bus voltages or currents when the turn-on occurred. On Tuesday, March 20, the high rail to chassis short in the CAPS instrument returned, generating the same condition that existed at the time the instrument was turned off. However, based on the tin whisker model developed by the NESC team, this condition is believed to be understood and is not expected to cause any problems for either the instrument or the spacecraft. The CAPS instrument has been left powered on and is sequenced to operate as originally planned for the 75 kilometer Enceladus flyby coming up on March 27.
Having seen a forest of tin whiskers myself, that’s a pretty scary diagnosis. One assumes NASA takes extensive precautions, based on their experience, but … 15 years in hard vacuum and free fall will do odd things to spacecraft.
Remember those Toyota unintended acceleration problems? Guess what caused some of them: yup. Read their report to find out what makes metal whiskers so hard to detect. Hint: combine a minimum threshold voltage with a very low current capacity.
You could subscribe to the Cassini Significant Events newsletter.
The MOSFET tester spits out datasets using this tedious Arduino code:
void PrintHeader(void) {
Serial.println(); // Gnuplot group break
Serial.println("#-----------------------------");
Serial.print("# VGate: ");
Serial.print(VGateSet,3);
Serial.println();
Serial.print("# TSetpoint: ");
Serial.print(TSetpoint,1);
Serial.println(" C");
Serial.println("# VGS \tVDS \tID \tRDS \tC \tTime");
}
void PrintTempHeader() {
Serial.println(); // Gnuplot index break
Serial.println();
Serial.print("#T="); // ... index name
Serial.println(TSetpoint,1);
Serial.println("#=============================");
Serial.print("# Setting temperature to: "); // human-readable annotation
Serial.print(TSetpoint,1);
Serial.println(" C ...");
}
... later, deep inside the main loop ...
Serial.print(VGateSet,3);
Serial.print('\t');
Serial.print(VDrainSense,3);
Serial.print('\t');
Serial.print(IDrainSense,3);
Serial.print('\t');
Serial.print((IDrainSense == 0.0) ? 0.0 : (VDrainSense / IDrainSense),3);
Serial.print('\t');
Serial.print(Temperature,1);
Serial.print('\t');
Serial.print(millis() - StartTime);
Serial.println();
All that produces a text file formatted to work with Gnuplot, including a blank line between successive gate voltage groups to produce separate plot traces:
#T=0.0
#=============================
# Setting temperature to: 0.0 C ...
#-----------------------------
# VGate: 4.250
# TSetpoint: 0.0 C
# VGS VDS ID RDS C Time
4.250 1.200 0.000 0.000 1.0 1757
4.250 1.665 0.044 37.851 1.0 1861
#-----------------------------
# VGate: 4.500
# TSetpoint: 0.0 C
# VGS VDS ID RDS C Time
4.500 0.003 0.000 0.000 1.0 2038
4.500 0.016 0.044 0.370 1.0 2143
... snippage ...
4.500 0.212 1.953 0.108 0.9 6105
4.500 0.216 2.001 0.108 0.9 6210
Which produces a plot like this:
IRFZ44
It’d be handy to automatically generate labels for the gate voltages, but I haven’t been able to figure out how to read values from the dataset and plunk them into the label strings. You can, however, select blocks of gate voltage and superblocks of temperature with a bit of effort.
The Bash script that feeds Gnuplot looks something like this:
#!/bin/sh
#-- set plot limits
tx=3
vgs_min="4.0"
vds_max="0.2"
rds_max=100
rds_tics=$((${rds_max} / 4))
id_max="2.0"
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
base="${1%.*}"
echo Base name: ${base}
ofile=${base}.png
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 "${base}"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set xlabel "Drain-Source Voltage - VDS - V"
set format x "%4.2f"
set xrange [0:${vds_max}]
#set xtics 0,5
set mxtics 2
set ytics nomirror autofreq
set ylabel "Drain Current - ID - A"
set format y "%4.1f"
set yrange [0:${id_max}]
#set mytics 2
set y2label "Drain Resistance - RDS - mohm"
set y2tics nomirror autofreq ${rds_tics}
set format y2 "%3.0f"
set y2range [0:${rds_max}]
#set y2tics 32
#set rmargin 9
set datafile separator "\t"
#set label 1 "Temp index = ${tx}" at 0.81,0.55 font "arialbd,18"
set label 2 "VGS >= ${vgs_min} V" at 0.11,0.55 font "arialbd,18"
plot \
"$1" using 2:((\$1 >= ${vgs_min})?\$3:NaN) index $tx:$tx with lines lt 3 lw 2 title "ID" ,\
"" using 2:((\$1 >= ${vgs_min})?(\$4*1000):NaN) index $tx:$tx axes x1y2 with lines lt 4 lw 2 title "RDS"
EOF
The variables up near the top control the plot limits; it’d be nice to have a complex Bash script that prompted for values, had useful defaults, and fed all that into Gnuplot. Given what I’m doing, it’s easier to just keep the Bash script open in the portrait monitor, watch the results on the landscape monitor, and twiddle until it looks right.
This script produces a plot for a single temperature range based on the superblock index tx; you can select a single block using index name (along the lines of “T=0.0”), but you can’t select multiple such blocks in a single plot statement.
Selecting gate voltages requires testing the first column for a match with the trinary operator and assigning the data value for lines that don’t match to the not-a-number value NaN to prevent it from appearing in the plot:
((\$1 >= ${vgs_min})?\$3:NaN)
All in all, the whole apparat makes for a fairly brittle set of code, but the plots come out ready for printing and that makes up for a lot.
The 120 m 50 V BUZ71A that served as the crash test dummy while I got the thing working:
BUZ71A-overview
A detail of the interesting area near the origin:
BUZ71A-detail
The datasheet drain resistance values are the maximum values, so they’ll generally be higher than what I measure.
A plastic-encapsulated W7NB80 with a 1.9 (!) drain resistance, due to its 800 V (!) rating:
W7NB80-overview
Hold the gate voltage constant at 10.0 V and step the temperature from 0 °C to 50 °C:
W7NB80-Temp
I haven’t figured out how to get the actual temperatures from the Gnuplot input dataset to the graph without knowing them in advance. The “index” is simply the 0-origin block number, which conveniently (and coincidentally) lines up with the 0 °C to 50 °C temperature range.
An overview of a 400 m 200 V IRF630:
IRF630-overview
The juicy part:
IRF630-detail
And the variations with temperature:
IRF630-Temp
A 1.5 200 V IRF610, another high-resistance transistor:
IRF610-overview
The temperature variations:
IRF610-Temp
The winning entry for high resistance, though, is the 500 Ω (!!!) BSS127 that emerged from a paper on current sensing using mirror FETs for temperature compensation. It has a 600 V rating, but I have no idea why such a high drain resistance makes any sense in a SOT-23 package. They’re obsolescent and I won’t buy any just to have ’em around.
Just for completeness, a 1 1% resistor:
Resistor – 1.0 ohm
And a 100 m 1% resistor:
Resistor – 0.1 ohm
It turns out that the wire leads I soldered on contributed 6 m to the total, so the tester actually reports the truth! I checked that by passing 1.000 A through the resistor, which put 100 mV at the base of the resistor pins, then measuring 106 mV at the end of the wire leads. One can quibble about voltmeter accuracy, but it’s pretty close and much better than the ohmmeter accuracy at that resistance.
The firmware forces 0.0 for drain current identically equal to 0.0 (it’s a floating point number cast from a 10-bit unsigned integer) to avoid numeric explosions. The next few points away from the origin show the effect of small errors on small measurements; the voltage resolution is 15 mV and the current resolution is 2.5 mA; you can actually see the steps near the origin.
All in all, a fun project…
Need the datasheets? Ask your favorite search engine for, say, IRF610 datasheet. That should do the trick.
The Smell of Molten Projects in the Morning 