Friday, 12 June 2009

What NOT TO design

This is an excerpt from TOI of 10-June.
"Back in 1960's, American space agency NASA was faced with a major dilemma. Astronauts needed a pen that would write in the vacuum of space. NASA got cracking into developing the $1.5 million gravity immune 'astronaut pen'.
At the same time, the Russians too were faced with the same dilemma. However, they used a pencil instead!"

How very relevant. It is important that we designers do not lose track of the solution and go only after technology for technology's sake. We should use technology for Solution's sake.

Sunday, 7 June 2009

LED Nightlight Fades Out in a Few Short Weeks | Made by Monkeys | Blog on Design News

LED Nightlight Fades Out in a Few Short Weeks

April 15, 2009


In theory, a LED light should last for ten years or so, unlike the typical 4W incandescent lamps used in night lights that seem to burn out in only a few months. But as engineer and founder of the website Discover Circuits Dave Johnson discovered, this Chinese-made unit from Costco (left side in photo) didn’t last but 12 weeks.

“I bought a pack of three of these night lights, made by Elumina Lighting Technologies, for about $15. The unit has a pushbutton switch to toggle between settings (dim and bright) and a CdS photocell that turns off the device during the day. Inside are three white LEDs, wired in series. When I first plugged the device in, it seemed to emit an acceptable amount of light. But in a short time, the light gradually faded until it was virtually useless.

This has happened to me several times with other inexpensive LED lights. I think some manufacturers from China are using inferior phosphors inside the LED assembly, which fatigue after only a few hundred hours. Opening the thing up, I traced out the circuit and determined it was one that I could easily modify.”

Dave made some component value changes and pulled out the three dim LEDs and replaced them with ten high quality, super bright surface-mounted units from Osram Opto at $1 each.

So now for an extra $10 per unit (and therein lies the engineering trade-off!), the light now emits a nice bright white light and should last many years with no risk of someone taking a header down the stairs in the middle of the night!”

View additional product images and Dave’s redesigned circuit , which uses a classic series capacitor method to produce a current limiting LED driver, powered from the AC line.

A version of this post originally appeared on Electronics Weekly Made by Monkeys blog.