Giorgos Lazaridis writes:
Some time ago i uploaded a breathing LED circuit with the 555 timer chip. It became very popular and i received many comments and emails with people that made this circuit and worked fine, as well as comments with people that had troubles converting it to operate at 12 volts supply. It was designed to operate with 5 volts, because i plan to use it for a future PC mod. Since the PC power supply has 5 volts output, and since the LEDs that i plan to use require 3.8 volts to operate, choosing 5 volts for supply was the best choice to minimize power dissipation on the transistor.
Converting the original circuit to operate at 12 volts is not a big deal, but it requires some transistor knowledge. The only parts that should be changed were the biasing resistors R4 and R5. But i decided to take it one step further. I decided to make a more flexible breathing circuit. The new version as 2 more functions: It has an adjustable voltage oscillation amplitude, and an adjustable output DC offset. What this means is that it can be easily adjusted to operate with different LEDs. If for example the load is a 12V LED strip with operating voltage range 8 to 12 volts, the circuit can be adjusted to provide exactly this: 8 to 12 volts output. Similarly, it can be adjusted to operate with a high brightness LED that has voltage range from 2.4 to 3.8 volts.
Flexible 555 LED Pulsing (Breathing) Circuit - [Link]
Giorgos Lazaridis writes:
During this very long period that my PC went bad, i had the time to do many thing like finishing the PC case mod that i began like two years ago… So i connected the power button, the reset button and the audio controls. The rotary encoder will be used for my next project that will be a gigantic scriptable 8-channel PC fan controller.
Now, regarding the power button, it has a blue LED that light when the HDDs are operating (write or read process). The effect is very cool, but i want to make it cooler. I want the LED to blink when the HDDs are used, and when no Read/Write operation occurs i want the LED to breath. A breathing LED is the effect that the LED turns on and off by fading in and fading out, which gives the feeling of “breathing”…
A 555 Breathing (Pulsing) LED - [Link]
RGB LED strips: an overview @ Nut & Bolt. David writes – [via]
An addressable RGB LED strip is like a one pixel high color screen. You can do awesome things with them: crazy lighting effects, information displays and even low resolution video. There are many different types of RGB LED strips on the market. Here is an overview of addressable led strips I evaluated for Stripe. I’ll tell you a bit about different controller chips, electrical specifications and software libraries to help you make a choice.
Adafruit LPD8806 LED strip is looking good! - [Link]
RGB LED Ring V2 — sequels don’t have to be bad @ My 2µF – [via]
This is the successor to my old (and lame) RGB LED Ring project.
Version ’2.0 alpha’ – an intermediate step to true enlightenment – uses one LED driver IC and 3 P-channel MOSFETs cycling through the primary colors. This requires special attention in the code to attempt color balancing (forced dot correction at all times).
As of ’2.0 beta’ (likely to become the final version) it comes with 3 dedicated constant current LED driver chips (MBI5168), which completely avoids multiplexing the LEDs and boosts brightness again. Color balancing is done entirely in hardware using 3 potentiometers. The hardware differences should be taken care of in the core part of the demo code, ‘User-land’ code is mostly the same.
RGB LED Ring V2 – sequels don’t have to be bad - [Link]
Try making a double led dice with 14 leds driven only by 4 available pins of an Atmel Attiny13a. I did it, and it worked:
14 leds can be driven by a technique called charlieplexing when not many microcontroller pins are available. This technique works from the fact that leds are diodes and that those diodes have a little voltage drop. In the network of leds, you can make one led turn on by applying a voltage smaller than twice the voltage drop of a led. In this way, only one led lights up. The other leds do not turn on because the voltage is not high enough.
To make all the leds light up you must cycle through all the leds very fast. Only one led can be turned on at a time. If you cycle through all leds very fast they all seem to be on at the same time to the human eye.
Charlieplexed double led dice - [Link]
Steven Keeping writes:
As high brightness LEDs become practical alternatives to incandescent and fluorescent light sources, manufacturers are under pressure from a skeptical public to publish realistic operational lifetime figures.
Accurate lifetime estimates for LEDs operating in specified conditions would help designers select the best device for their product, manufacturers set warranty periods, and consumers compare cost-of-life of LEDs with conventional light sources (an important justification given LEDs’ higher initial purchase price).
Consumers understand that an incandescent bulb may last 1000 hours and a compact fluorescent light (CFL) perhaps five times that before catastrophic failure, but are less familiar with solid state lighting sources.
The problem for the manufacturers is that properly driven and thermally managed LEDs can last for years, so sitting around and waiting for an LED to fail is not a practical test regime. Secondly, an LED can either fail catastrophically or, more likely, suffer from a slowly diminishing output. At what point should such a fading LED be considered as ‘failed’?
This article discusses the standardized test method for determining approximately how long a high brightness LED will remain “fit for use.” The article then goes on to describe the latest improvement to this test which increases the accuracy of the result, then discusses why this is still not an equivalent of the “lifetimes” cited for conventional light sources – and whether that really matters.
Determining LED Rated Life: A Tricky Challenge - [Link]
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 installing 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.
Fun with LEDs - [Link]
Kristin Lewotsky writes:
LEDs have a well-deserved reputation for high-efficiency operation, not to mention high reliability. Properly specified and implemented, LEDs should and do satisfy virtually every lighting application. Still, there are times when actual device lifetimes fall short of the specified ideal. LEDs are wide-bandgap semiconductor devices. As a result, they have far more complex and varied failure modes than the incumbent technologies. Unlike an incandescent lamp, where failure is fairly simple (the bulb produces light until the filament breaks), with an LED, the failure modes range from mechanical and electrical to material.
Understanding and Preventing LED Failure - [Link]
Paul Dietz, William Yerazunis, Darren Leigh write:
A novel microprocessor interface circuit is described which can alternately emit and detect light using only an LED, two digital I/O pins and a single current limiting resistor. This technique is first applied to create a smart illumination system that uses a single LED as both light source and sensor. We then present several devices that use an LED as a generic wireless serial data port. An important implication of this work is that every LED connected to a microprocessor can be thought of as a wireless two-way communication port. We present this technology as a solution to the “last centimeter problem”, because it permits disparate devices to communicate with each other simply and cheaply with minimal design modification.
LEDComm: Bidirectional Communications using LEDs - [Link]
Mini RGB LED video wall using a Netduino and an Adafruit LED strips… [via]
16×10 RGB LED display built with an Adafruit LPD8806 LED strip and a Netduino mini as the controller. The display is capable of showing over 2 million colors. What’s not to like about RGB LEDs? With their bright, mesmerizing glow, often capable of displaying millions of colors, they’re a great to way to catch the attention of the viewer. Now, what if you had a 5 meter long RGB LED strip, loaded with 160 RGB LEDs to play with? Oh, the possibilities… It so happens that Adafruit, in their infinite wisdom, carries a very nice RGB LED strip, powered by a LPD8806 driver and encased in a waterproof sleeve. What about turning it into a mini video wall for instance? Think ‘Times Square’, just smaller
Mini RGB LED video wall using a Netduino - [Link]