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Archive for May 16th, 2009

Remote Control Button Shield

Button shield in place

Button shield in place

Mary was giving one of her vegetable gardening presentations and had the projector go into Mute mode all by itself. It’s hard to debug something like that under pressure, but (as nearly as we can tell) the projector’s remote control (!) got squashed inside the tote bag and managed to tell the projector to go mute itself…

The remote control has buttons that stand proud of the surface by about 2 mm and, worse, they’re exposed from all sides. There seems to be no way to turn the mumble thing off, other than by removing the batteries, so I conjured up a quick-and-dirty button shield. Not the fanciest thing I’ve ever made, but it’s sufficient for the purpose.

[Update: Apologies to all you Arduino fans who think this should have something to do with a remote-control circuit board plugged atop a Diecimila, but I think the Arduino designers could have picked a more descriptive term than “shield”. Plenty of folks seem to arrive here by searching for the obvious keywords and go away unhappy. If you’re looking for Arduino stuff, click on the obvious tag in the right-side column that’ll call up everything I’ve written about on the subject… ]

Sizing the perimeter

Sizing the perimeter

I thought about making a tidy form-fitting slab that would fill the entire space between the button matrix and the case, but that gets into curved edges and fussy fitting; fortunately, I came to my senses. Without wanting to make a prototype to get the second one right, I simply trimmed the outside of the polycarbonate slab to a ruthlessly rectangular 33×50 mm. That gives about 2 mm clearance on each side of the button matrix and fits with about 1 mm clearance from the case. The lengthwise dimension is what it is.

The 29×46 mm pocket must be about 3 mm deep to clear the button tops.

The G-Code came from the Hugomatic pocketRect2points generator, which worked just fine; normally I hammer out my own G-Code, but I was leaving on a trip the next day. The cut depth of 1 mm per pass was probably too conservative. A cutting speed of 300 mm/min with a 2000 rpm spindle worked reasonably well with water cooling.

Pocket milling with water coolant

Pocket milling with water coolant

A 1/8″ end mill produced corner radii that matched the buttons fairly well, which means it took a loooong time to chew out the pocket. The picture shows the mill knee-deep in a pool of water and swarf; I vacuumed the chips out at the end of each pass and added more water.

Double-stick tape held the polycarb & sacrificial plate to the tooling plate, which worked surprisingly well given that I just wiped the grunge off and squashed it down. A machinist’s square aligned the rectangle closely enough and, of course, I used the laser aligner to set the coordinate zero to the left-front corner.

For lack of anything smarter, a rubber band holds the shield in place on the remote. I thought about fancy hinges and Velcro and stuff like that, but the projector is used by non-technical folks and, as nearly as I can tell, the remote control never gets used at all.

Quick and dirty, indeed: about two hours, first doodle to snapping the rubber band, including a bit of time wasted on an ancient G-Code generator that spat out bad coordinates.

Plus time to write this up, natch…

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