Tour Easy Rear Running Light: Circuit Support Plate

Building the circuit support plate for the amber front running light was entirely too fiddly:

1 W LED Running Light - baseplate dry assembly
1 W LED Running Light – baseplate dry assembly

This was definitely easier:

Running Light Circuit Plate - solid model
Running Light Circuit Plate – solid model

Two pins fit in the small holes to align it with the LED heatsink, with an M3 stud and brass insert holding it in place:

Tour Easy Rear Running Light - circuit plate attachment
Tour Easy Rear Running Light – circuit plate attachment

The rectangular hole around the insert let me glop urethane adhesive over it to lock it into the plate, with more goop on the screw and pins to unify heatsink and plate.

The LED wires now emerge from the heatsink on the same side of the plate, simplifying the connections to the MP1584 regulator and current-sense resistor:

Tour Easy Rear Running Light - regulator wiring
Tour Easy Rear Running Light – regulator wiring

The paralleled 5.1 Ω and 3.3 Ω resistors form a 2.0 Ω resistor setting the LED current to 400 mA = 1 W at 2.6 V forward drop. They’re 1 W resistors dissipating a total of 320 mW and get barely warm.

The resistors and wires are stuck in place with clear adhesive, so things shouldn’t rattle around too much.

The OpenSCAD source code as a GitHub Gist:

// Circuit plate for Tour Easy running lights
// Ed Nisley - KE4ZNU - 2021-09
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
ID = 0;
OD = 1;
LENGTH = 2;
inch = 25.4;
//----------------------
// Dimensions
// Light case along X axis
LightID = 23.0;
WallThick = 2.0;
Screw = [3.0,6.8,4.0]; // M3 OD=washer, length=nut + washers
Insert = [3.0,4.2,8.0]; // splined brass insert, minus splines
InsertOffset = 10.0; // insert from heatsink end
PinOD = 1.6; // alignment pins
PinOC = 14.0;
PinDepth = 5.0;
Plate = [50.0,LightID,Insert[OD] + 4*ThreadThick]; // overall plate size
WirePort = [10.0,3.0,2*Plate.z];
NumSides = 2*3*4;
//----------------------
// 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,
$fn=Sides);
}
// Circuit plate
module Plate() {
difference() {
intersection() {
cube(Plate,center=true);
rotate([0,90,0])
cylinder(d=LightID,h=2*Plate.x,$fn=NumSides,center=true);
}
rotate([0,90,0]) rotate(180/6)
translate([0,0,-Plate.x])
PolyCyl(Screw[ID],2*Plate.x,6);
rotate([0,90,0]) rotate(180/6)
translate([0,0,-Plate.x/2 - Protrusion])
PolyCyl(Insert[OD],Insert[LENGTH] + InsertOffset + Protrusion,6);
translate([-Plate.x/2 + InsertOffset + Insert[LENGTH]/2,0,Plate.z/2])
cube([Insert[LENGTH],Insert[OD],Plate.z],center=true);
for (j=[-1,1])
translate([-Plate.x/2,j*PinOC/2,0])
rotate([0,90,0]) rotate(180/6)
translate([0,0,-PinDepth])
PolyCyl(PinOD,2*PinDepth,6);
for (j=[-1,1])
translate([0,j*(Plate.y/2 - WirePort.y/2),0])
cube(WirePort,center=true);
}
}
//- Build it
Plate();

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