26 April 2016
BUILD IT YOURSELF
Every night, the kitchen under-the-counter LED lighting
makes getting that midnight
snack a breeze. For years,
though, I lamented that there
was no on at dark/off at light
automatic functionality. In
addition, every year in the
Pacific Northwest where I live,
severe windstorms rip through
— windstorms that take down
trees and power in their path,
plunging the street into
darkness. Many times, I
power-up the household DC-to-AC inverter ahead of time
when I suspect an outage.
darkness comes faster than I
can set flashlights out or
power-up. Last November's
outage during dinner
preparation meant a call for
action: Put automatic on/off
and battery backup on the
system. It was high time for a
BBLIS: Battery Backed-Up LED
By Jim Lacenski
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The first design criteria were obvious: Have an auto on/off and a
battery backup. I knew I wanted to have 12 volts output to the LED set as
before, and keep my thrift-store sourced 12 volt adapter. Next, I wanted to
be able to use just a few batteries, and have a very power-efficient design.
The system would need to fit onto the same credit card sized solderable
breadboards that I use for most projects.
Normally, I would reach into my processor bin and grab a Microchip
processor. The surprise arrival of some Texas Instruments’ (TI) Launchpads
onto my doorstep last Christmas Eve provided a “let’s learn something
new” moment, so I decided to take the plunge and use a TI processor
I contemplated using rechargeable batteries. Due to the very
infrequent use and low current drain, designing to inexpensive “heavy
duty” or — at most — alkaline batteries was a better fit in this application.
With the local “Freight” tool store giving away 24 packs of AA cells at the
time, I knew that their heavy duty AA batteries would be my batteries of
choice. Four of these would also be easy to hide under the cabinet edge.
A simple PWM (pulse width modulation) step-up converter would form
the bridge between the four AAs and the 12 volt LED strip.