Fun with LEDs


Posted on Feb 5, 2014

I have recently stumbled upon some LED strip at my local electronics shop and decided to give them a try. I bought some which I used to replace the spot lights in the kitchen. It is cold white, which is surprisingly good, especially for night time illumination (think moonlight like hue). It works at 12V and consumes about 0. 25A per meter. After in


Fun with LEDs
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stalling the strip, some automation proved to be necessary, and so the following circuits were built. The goal in mind was to keep things as simple as possible and use only parts I had at hand, which is why the solution might not be the best. The hallway spotlights got new white LEDs as well and a light sensor. Tiny PIR sensors will turn on the lights in the kitchen and bathroom when someone comes in range. The sensors are rather popular modules using a BISS0001 IC; they provide a 3. 3V level for an adjustable time when motion is detected. Overall the results are great. The hallway is lit at night, the there is a small automatic light for the bathroom and the automatic kitchen light is bright enough even for day time illumination of the sink and counter. The slow turn off provides both a visually pleasing effect and a warning in case someone stood still long enough to make the light go off. I am still looking for a simple solution to produce the same effect on turn on, but without the delay. The circuit is used to turn on the hallway lights. T2 will turn off when it is dark enough, allowing T1 to turn ON and light up the LEDs. The threshold is determined by the divider formed with a photo resistor and a potentiometer. I gave up using a constant current supply in the favor of a simple current limiting resistor because at around 100mA of current (set with R3) there is no danger of thermal runaway. The PIR sensors themselves...




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