it is Saturday morning and i have no lightbox.

i do have a cardboard box and a boring white pillowcase, but neither of these things is a lightbox. thankfully, we are clever monkeys, and we can turn boring things into awesome things.

it is time for

Saturday Morning Lightbox

we live in a magical world. a world where if you ask for an inch, you can get almost exactly one inch.

you can run your calipers down the side of a box, scratching a thin line exactly 1 inch from the edge. it is fast and easy! your ruler and pencil will not be missed.

then you can scissor up those lines, and it will look like this.

but scissors are only useful for cutting flaps. a craft knife is better for cutting holes in the sides.

if you lack a craft knife and won't go to the store, a fruit knife will do.

i am an art knife, but sometimes i cut fruit.

i have a box, but i only want the form of a box. i will keep cutting until just the form is left.

bereft of box, the form is flimsy, and must be strengthened.

and now dear pillowcase, lend your feel to the form.

lunchtime!

...

i sailed away on a sea of spinach for several hours. but now i am finally ready to go to The Store.

it is time for

Saturday Evening Lightbox

they are labelled '24-inch square hardwood dowels'. they are sticks.

armed with sticks and paper, i continued adorning my box-form. the sticks were taped into the front edges for strength. the paper was hung from rear-edge to floor to create a seamless white background.

the pillowcase and cardboard box have been born anew. it is time to photograph my favorite things: circuit boards.

#1, DSP 01. my first digital signal processor. two input channels, six output channels, 24-bit data converters everywhere. i'll be writing about this one pretty soon.

my logo on a thing :D

#2, Printed Cubist Board. the most time-consuming circuit board design in my short career. partly because it's huge and crazy, partly because I had no idea what I was doing when i made it.

*ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn*

Tshen2 2014

(or, misusing Eagle for mechanical CAD)

problème du jour:

build a fixture which holds a large circuit board three inches off the ground
at a 30-degree angle
with lots of space underneath for wiring
and a temperature range of -40 to +85 Celsius
in 48 hours.

how fun! let's go.

Constraints 1 & 2 & 3: 30-degree angle, 3 inches off the ground, space underneath for wiring

we could have accomplished 1 & 2 by stacking solid materials underneath the circuit board, until we'd built a hill, and it would have the right height and angle. but 3 won't let us do that. the thing must be supported lightly, with free space underneath.

this sounds like a precision job. a lasercutter job!

Constraint 4: -40 to +85 Celsius temperature range

now this gets thorny. lasers cut materials by heating them until they vaporize. but this material must be ok with high temperatures. conflict?

Option 1: acrylic. the laser nerd's favorite. but acrylic sheets get sad and bendy at 85 Celsius. no can do!

Option 2: polycarbonate. super tough. chill with hot, hawt with cold. when cut with a laser, it releases poison. i prefer breathing not-poison.

Option 3: white Delrin. tough enough. does its job. cuts without hastening death. Delrin it is!

with a wide temperature range, you have to worry about thermal expansion of materials. my fixture will cup the circuit board, and it will contract faster than the circuit board when things get cold, so it must be too big at room temperature.

how too big?

linear thermal expansion coefficient of Delrin: 122ppm/Celsius

linear thermal expansion coefficient of FR4: 14ppm/Celsius

difference in coefficients: 108ppm/Celsius

-40 Celsius is 65 Celsius below room temperature.

fractional thermal contraction at -40 Celsius = (108ppm/Celsius)*(65 Celsius) = 7020ppm

the circuit board is 12 inches long.

thermal contraction at -40 Celsius = (12 inches)*(7020ppm) = 0.08 inches

so we should oversize our fixture by 0.08 inches.

Constraint 5: do this in 48 hours

we've already started :D

i do mechanical drawings in Eagle. Solidworks hates me for this one weird trick. Eagle is for making electronics, not lasercutting plastic. but Eagle lets you draw lines on layers, and save those layers as EPS files, and your lasercutter thinks EPS files are delicious.