Archive for February 28th, 2014
Mary wants more light on her free-motion quilting, right where the needle meets the fabric. I proposed LED strip lights on the machine arm, in addition to rebooting the end cap lamp into the current millennium, which requires:
- No snagging on a bulky quilt shoved through the machine
- Not completely butt-ugly
- Reasonably durable
I picked up reels of cool-white and warm-white waterproof LED strips (12 V, 3528-size chips, 5 m, 600 LED, 25 mm segments) from the usual eBay supplier, who promptly charged for both and shipped only the warm-white reel. Cool-white LEDs will be a better color match to daylight from the window and the little Ottlite she uses for detail work, but I ran some prototypes while we wait for the replacement.
The Chinese New Year really comes in handy as an excuse for screwing things up and not responding for a week or two. ‘Nuff said.
They’re similar to the RGB LEDs from a while ago, with even gummier “waterproof” encapsulation. I got double-density 600 LED strips to put more light emitters across the arm:
The smaller 3528 SMD LEDs (vs. 5050 chips in the others) allow a narrower strip and the double-density layout means each three-LED segment is half as long long. The as-measured dimensions work out to:
- 25.0 mm segment length
- 8.2 mm strip width
- 2.5 mm thickness
The sealant thickness varies considerably, so I’d allow 3.0 mm for that in case it mattered. It slobbers over the edge of the strip here and there; allowing at least 9.0 mm would be wise.
The SMD resistor in each segment is 150 Ω. A 5 segment length drew 85 mA @ 12 V = 17 mA/segment. Boosting the voltage to 12.8 V got the current to the expected 100 mA = 20 mA/segment.
The LEDs are noticeably less bright than the 5050 LEDs, even at 20 mA/segment, but I think they’ll suffice for the task.