Led category

Driving LEDs


Emanuele @ dev.emcelettronica.com published an article on how to drive LEDs:

The LEDs (Light Emitting Diode) are diodes whose basic characteristic is the ability to emit light when they are passed through a current that flows from P to N region. At each recombination between the charge carriers (electrons and holes), on PN junction region, a photo emission is generated, and the total quantity of emitted photons, and therefore the light intensity, is proportional to the current intensity that passes through them. The emitted light has a spectrum – wavelengths distribution – that is defined according to the materials used in the realization of the diode PN junction, although it partially depends on the current intensity and on the junction temperature.

Driving LEDs – [Link]

A Connected Lamp to Wake Me Up


Limpkin has modified his IKEA lamp to use 10W LEDs.

So for some reason I bought 2 IKEA lamps at a flea market. As IKEA furniture has a long history of being hacker-friendly, I figured they shouldn’t be an exception to the rule.
My plan? Fit a few 10W RGB LEDs in there together with an ESP8266 to use the final result as an alarm clock.

When you are dealing with a LED consuming that much current, you can’t simply use a series resistor as the latter would need to dissipate R*I² in heat. I’m therefore using a dedicated LED driver that automatically adjusts the LED voltage to match a given current. As you can guess, it isn’t much different than a standard step-down and just uses a shunt resistor to measure the current flowing through the LED.

A Connected Lamp to Wake Me Up – [Link]

Fake TV Security Light


by Marcus Jenkins:

This gadget steps up the game from leaving a light on at home when you’re out. Place it near a window to make it look like somebody’s at home watching TV.

The idea of leaving a light on at home while you’re out is to give the burglar an uneasy feeling that somebody’s at home and it might be worth trying the next house along instead. A TV on at night plays a constantly-changing light-show against your window which really does say I’m at home and I’m awake. Of course, you could leave a real TV on but that’s an eco-disaster since TV’s consume 50W at best and hundreds at worst. Plus you might not want to be burning your TV in for days on end if you’re not at home.

Fake TV Security Light – [Link]

Voltage indicator transitions between colours


by Einar Abell @ edn.com:

This Design Idea gives two versions of an indicator light that changes from green to red as a battery discharges. There are many circuits that do this sort of thing, but all the ones I have seen are too complex and costly for my taste. This DI shows a method that uses an absolute minimum of low cost parts: a dual-color LED and four other parts.

Voltage indicator transitions between colours – [Link]

WifiPixels – ESP8266 Wifi unit combined with a NeoPixel


WifiPixels are a combination of a ESP8266 Wifi unit combined with a NeoPixel(Addressable RGB) LED ring all in one. http://wiki.protoneer.co.nz/WifiPixels Video here.

WifiPixels – ESP8266 Wifi unit combined with a NeoPixel – [Link]

Tutorial on the Design & Implementation of an FPGA RGB LED Matrix Driver

In this episode Shahriar and Timo demonstrate the design methodology of an FPGA based 32×32 RGB LED matrix driver. Timo has kindly devoted some of his time to describe the block diagram and the thought process which goes into designing this type of FPGA display driver. The various components of the overall system (PLL, UART, and Display Controller) are shown along with the simulation data. The outputs of the Spartan-6 FPGA board are then measured using a Keysight S-Series oscilloscope. The design of the RGB matrix is also demonstrated using a custom clock interface sent wirelessly to the unit via Bluetooth.

Tutorial on the Design & Implementation of an FPGA RGB LED Matrix Driver – [Link]

PCA9550 LED Driver With Programmable Blink Rates

This project introduces the use of PCA9550, an LED driver that causes the 2 LEDs to ON/OFF or in a flashing state at programmable rate. It has 2 selectable, fully programmable blink rates between 0.172Hz and 44Hz or 5.82 seconds and 0.023 second respectively. Its internal oscillator does not require external components and I2c bus interface logic is compatible with SMBus.

The PCA9550 LED blinker drives LEDs in I2C-bus and SMBus applications where it is necessary to limit bus traffic or free up the I2C Master’s (MCU, MPU, DSP chip set, etc.) timer. The uniqueness of this device is the internal oscillator with two programmable blink rates. This LED blinker requires only the initial set-up command to program BLINK RATE 1 and BLINK RATE 2 (i.e., the frequency and duty cycle). From then on, only one command from the bus master is required to turn each individual open-drain output ON, OFF, or to cycle at BLINK RATE 1 or BLINK RATE 2. Maximum output sink current is 25 mA per bit and 50 mA per package. Any bits not used for controlling the LEDs can be used for General Purpose I/O (GPIO) expansion. The active LOW hardware reset pin (RESET) and Power-On Reset (POR) initializes the register to their default state, all zeroes, causing the bits to be set HIGH (LED OFF). One hardware address pin on the PCA9550 allows two devices to operate on the same bus.

LED drivers can enable dimming and color changing or sequencing of LEDs initiated by preset commands, occupant presence, or manual commands. Most LED drivers are compatible with commercially available 0V to 10V control devices and systems like occupancy sensors, photocells, remote controls, architectural and theatrical controls, and building and lighting automation systems.

PCA9550 LED Driver With Programmable Blink Rates – [Link]

16-Bit I2C-Bus LED Dimmer

This project is devised for LED dimming using NXP Semiconductors’ PCA9532 16-Bit I2C-Bus LED dimmer. A lot of solid-state lighting applications require control over the emitted intensity of light for both functional and aesthetic requirements. Some of these applications also require a full dimming capability from fully ON to fully OFF. LED dimming potentially improves light source efficacy and lifetime.

The PCA9532 is an IC that is designed for controlling 16 LEDs over and I2C bus. It also includes the logic to act as an I2C slave device as well as the drive capability for directly driving LEDs. As well as being able to switch each of the LEDs ON and OFF independently, the PCA9532 also has two fully programmable PWM controllers that can be used to control up to 16 LEDs. Each PWM channel has a programmable period ranging from 0.6Hz to 152Hz, and a programmable duty cycle from 0-100%. This means the LEDs can be set to blink steadily and visibly, or dimmed. In this circuit, 13 LEDs are connected on pins LED0-LED12. The 1kΩ pull resistors required are fitted to the 5V supply. Once programmed, the internal oscillator allows the I2C bus to be disconnected from the PCA9532 with the LED continuing to be dimmed, something not possible with normal GPIOs. This enables electronics manufacturers to have supplementary LED dimmers in their systems, while freeing up the microcontroller and the I2C bus for more efficient operation of the system.

The I2C are targeting applications ranging from mobile phones to servers in computing, communication, and networking applications. Having a frequency range of 160Hz to once every 1.6 seconds, with a duty cycle range of completely off to 99.4% on allowing both dimming and blinking of LEDs. These new 2-, 4-, 8-, and 16-bit devices allow designers an easy way to build systems with more dimming LEDs than previously possible using just basic General Purpose I/Os (GPIO) or microcontrollers (MCUs). Manufacturers of applications such as cellphones and servers are increasingly requiring multiple blinking and dimming LEDs for eye-catching keypad lighting applications, as well as practical purposes such as status indication. The new PCA953x LED Dimmers allows more system flexibility by off-loading the LED power consumption and by eliminating the programming of the MCU.

16-Bit I2C-Bus LED Dimmer – [Link]

A low-cost 0.5A 33V LED driver module with 90+% efficiency

LG-LED-150702-DF-Futuro Low-cost LED driver Design FigA

by Valentin Kulikov @ edn.com

This article describes simple constant current driver module with fast PWM input that can be used for driving medium and high power LEDs. The module uses an integrated constant-current output, DC-DC buck converter with output current configurable from 0.1 to 0.5A. This article outlines the schematic, design guidelines, operation, and performance of the low cost LED driver.

A low-cost 0.5A 33V LED driver module with 90+% efficiency – [Link]