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Electronics Schematics - L

LED (Light Emitting Diodes) Circuits

1.5 Volt LED Flashers #1: four circuits with description

1.5v LED FLASHER: This is a very basic little circuit built around the LM3909 IC. A list of components and values is included.

10 Channel LED Sequencer:  based on4017

10 LED Sequencer: in PDF format, text in Finnish

16 Stage Bi-Directional LED Sequencer:

2 LED Flasher: simple2- transistor circuit which blinks2- LEDs

2 Transistor LED Flasher #1:

2 Transistor LED Flasher #2:

28 LED Clock Timer 72 LED Clock: programmable clock Timer circuit that uses individual LEDs to indicate hours and minutes

3 Way Blinking LEDs:

40 LED Bicycle Light (555 Timer 6 Volt):

7 Segment LED Counter:

72 LED Clock:

9 Second Digital Readout Timer #2:

9 Second LED Relay Timer #2:

AC Line Powered LEDs:

Adjustable Flashing Led:

Alternating LED Blinker uses Four Parts: 03/26/98 EDN-Design Ideas /Grand Prize Winner1998

Alternating LED Flasher uses Minimal Parts: 11/20/97 EDN-Design Ideas / A pair of alternating flashing LEDs makes an excellent visual alarm, this alternating LED flasher is based on one LED with built-in flashing function and two transistors driving the other normal LED

Alternating LEDs Flasher: Mar-03

Analog LED Bar VU Meter: built around discrete components

Astable Multivibrator 1:

AT89C2051 / 4051 Driving Dot LED:

Audio LED VU Meter: built around discrete components

Back & Forth Flasher: for16 LEDs

Basic LM3909 LED Flasher: runs from1.5-Volt battery

Bicycle Back Safety Light: Flashing13 LED unit,3V supply Also suitable for jogger/walkers

Bicycle Safety Lights:

Big LED Clock:

Buck IC boosts battery voltage for white LED: 04/24/03  EDN-Design Ideas / White-light LEDs are finding their way into many markets that incandescent bulbs once served. Flashlights are among the newer applications in which reliability, ruggedness, and ability to control the power draw of the LEDs make these devices attractive. With incandescent bulbs, the power management for the device is a simple on-off switch.

Car Message Display: CaMeD was designed and built to be used in an automobile. Its purpose is to display various symbols/messages to the car driver traveling behind you. It uses1024 LEDs to form a32 x32 matrix display. A total of12 symbols/messages can be displayed,4 of them being user-definable by using a visual basic utility tool connected to the rs232 port of a PC. 

Circuit Controls Two LEDs With One Microcontroller Port Pin : 04/01/02 Electronic Design - Ideas for Design /  Microcontroller port pins can typically be driven either high or low, or else be put into an "input" or high-impedance state. This circuit uses the three states to drive two separate LEDs with one port pin.

Circuit drives mixed types and quantities of LEDs: 10/03/2002  EDN - Design Ideas /  Portable systems often use LEDs of different colors and in varying quantities of each color. Some examples are white for the display backlight, green for keypad illumination, and red for power. Typically, the LEDs derive power from at least two power supplies: one for "standard" LEDs (red and green) and one for white LEDs.

Circuit efficiently switches bipolar LED: 11/22/2001 EDN - Design Ideas / The circuit in Figure 1 represents one method to switch a bipolar, two-color LED using an SPDT mechanical switch or relay. This circuit wastes power and does not work properly if the power-supply voltage is not substantially more than the sum of the LEDs' forward voltages.

Connecting LED to PIC Micro I/O Pins:

Constant Current White LED Flashlight:

Create secondary colors from multicolored LEDs: 07/24/03  EDN-Design Ideas / It is well-known that simultaneously mixing two primary-color light sources, such as red and green, creates a secondary color, such as yellow. This mixing process commonly occurs in tricolor LEDs.

Dancing LEDs:  A LED sequencer, following the rhythm of music or speech 9 Volt Battery-operated portable unit

Diode & LED Tester:

Dual Alternating Flashing Light:

Dual Tandem Flashing Light:

DualGate Inverter Oscillator Saves Power, Boosts LED Brightness: 06/24/02 Electronic Design - Ideas for Design / An LED's brightness is directly proportional to the current through it, which creates a challenge for low-voltage and battery-powered applications.

Economical Circuit Drives White LEDs: 11/23/00 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit.

Expandable 16 Stage LED Sequencer:

Fading LEDs

Fading Red Eyes: can be used to slowly illuminate and fade a pair of red LEDs

Fantastic Atom Expander: "exploding atom" effect using 98 LEDs

Fire Lights: LEDs shimmer randomly as though on fire.  Circuit generates true random coin-toss output. 

Flasher Circuit : LED Flasher, suitable for Christmas Lights

Flashing Christmas LED Display:

Flashing High Intensity LED 3rd Brake Light: This circuit to make a flashing3rd brake light assembly was designed to be easy to locate all the needed components and reasonably in expensive to build.

Get More than Three Colors From a Dot Matrix LED : 06/04/98 EDN-Design Ideas

Grantronics Projects Christmas Tree : flashes LEDs mounted to Christmas tree shape PCB, kit from kitsrus.com

Holiday Map Display:

ICL7660 LED Flasher:

Inexpensive LED Drives Flash & Beep Circuit: 06/05/97 EDN-Design Ideas

Infrared LED Illuminator:

LED Amplifier:

LED Bar VU Meter:

LED Barograph Drive:

LED Chaser: simple10 LED chaser

LED Christmas lights :

LED doubles as emitter and detector: 08/16/2001 EDN - Design Ideas / Every junction diode exhibits some degree of photosensitivity when it receives light comprising an appropriate range of wavelengths. The spectral response of a junction diode depends on a variety of factors, including material chemistry, junction depth, and packaging.

LED driver combines high speed, precision : 08/21/03  EDN-Design Ideas / Applications such as turbidity measurement and densitometry require cleanly pulsed light sources with stable amplitudes. The LED driver in Figure 1 illuminates retinal neurons in a biological experiment that has similar requirements.

LED driver delivers constant luminosity: 06/12/03  EDN-Design Ideas / The circuit in Figure 1 is similar in principle to that of a previous Design Idea (Reference 1) but offers improved, more reproducible performance. The output current is almost constant over an input-voltage range of 1.2 to 1.5V and is insensitive to variations of transistor gain. Transistors Q1 and Q2 form an astable flip-flop.

LED Driver Displays Standing Wave Radio: 03/18/99 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit

LED Flasher & TRAC Pulser Work off AC Line: 01/15/98 EDN-Design Ideas

LED Flasher indicates Low Battery Condition: 01/02/97 EDN Design Ideas

LED Flasher, Two Transistor:

LED Flasher: built using two transistors and some other components

LED flasher-a :

LED flasher-b:

Motorcycle LED Lights Circuit

LED Light Dimmers uses only Two Lines: 03/21/02 EDN-Design Ideas /  PDF contains multiple circuits - scroll to find the one of interest -- This circuit provides32 steps of brightness control (from0 to100%) for a backlight or instrument panel, using just two general-purpose-microprocessor signals.  Although the circuit shows the circuit driving white LEDs, the load could also be a dc motor or an incandescent lamp. The basis of the circuit is a modified Schmitt-trigger relaxation oscillator controlled by MAX5160 digital potentiometer.

LED Mood Light: this LED circuit makes a nice lamp that is low power, runs cool, and has a long lifetime, operates from12V, puts out a warm yellow shade of light, the color may be adjusted by changing the number of red or green LED strings

LED or Lamp Flasher : Minimum parts counting. Designed for3V battery operation

LED or Lamp Pulser : Astonishing effect4.5 Volt supply

LED Pilot Light (AC or DC): LED current is constant between 6 and 8 mA at5 to30Vdc

LED Pulser With Audible Output:

LED Sign: uses two LED arrays to form a 7 X 10 matrix. It produces moving messages or animations stored in an EPROM.

LED Stroboscope: This simple LED Stroboscope circuit which I designed, maintains constant
brightness of the LED at all frequencies. This is accomplished by duty-cycle and pulse width control. It is useful for measuring the speed of motors. It can easily be calibrated using a watch so you don’t need a frequency counter.

LED Torch : A white LED torch that consumes just24 mW

LED7 Solar Tracker:

LEDs Flasher, Alternately: Classic astable multivibrator using2 transistors. Transistor is not critical. Try these:2N4401,2N2222, NTE123A, NTE123AP, NTE159, TUP/TUN and those in your junk box, you may find that most of them will work.

Light a white LED from half a cell: 06/12/03  EDN-Design Ideas / Whether you use them as indicators or to provide illumination, LEDs are hard to beat in efficiency, reliability, and cost. White LEDs are rapidly gaining popularity as sources of illumination, as in LCD backlights, but with forward voltages typically ranging from 3 to 5V, operating them from a single cell presents obvious difficulties.

Light Pollution Meter: LED brightness control circuit and a multimeter to compare light levels to LED level.

Linear Constant Current LED Lamp Dimmer: This circuits drives24 white light LEDs with an adjustable constant current.

Low Power LED Flasher : based on LM3909

Mains Operated Christmas Star:

McMurtrie's Self Powered Flashing LED : circuit which uses a LED as solar panel to charge a capacitor which flashes a LED, the LED will blink when the circuit is placed in bright light

Park Aid: 3-LEDs signal bumper-barrier distance Infrared operation, indoor use

PIC Micro LED Projects:

PIC16F84 LED Chaser:

Picxie 2 8x8 Animated LED Signboard:

Propeller Clock: a few light emitting diodes spin, precisely controlled by a PIC microprocessor, giving the illusion of a larger array.

Remote Solar LED Light:

Reset Circuit Provides Snappy Action: 04/29/99 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit

Rugged LED Brake Lights :

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Serial Comms to LED Driver:

Seven Component Regulated LED Lamp :

Signal Processor Adds LED Display: 06/05/96 EDN-Design Ideas

Simple Logic Probe uses Bicolor LED: 03/13/98 EDN-Design Ideas

Single cell lights any LED: 07/05/2001 EDN - Design Ideas / The circuit in Figure 1 allows you to light any type of LED from a single cell whose voltage ranges from 1 to 1.5V. This range accommodates alkaline, carbon-zinc, NiCd, or NiMH single cells. The circuit's principal application is in LED-based flashlights, such as a red LED in an astronomer's flashlight, which doesn't interfere with night vision.

Single FET Controls 2nd LED Array in SwitchMode LED Backlight: Maxim APP1871: Feb03,2003 /  A design in which the display is backlit (or frontlit) for extended periods needs an efficient circuit that drives the LEDs with a controlled current, and eliminates the wasted power associated with current-limiting resistors. A switch-mode boost design that regulates current instead of voltage accomplishes this purpose.

Single FET Controls LED Array: 04/12/01 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit.

Single LED indicates Two Power States: 12/05/96 EDN-Design Ideas / Uses a single bicolor LED to indicate both power-on and blown-fuse conditions

Solar Charged LED Flashlight:

Special Lighting : experiments with white LEDs

Telephone In Use LED Indicator:

Telephone in use Light:

Three Way Blinking LEDs :

Two LED Flasher: simple2- transistor circuit which blinks2- LEDs

Two LEDs Perform Rudimentary Spectral Analysis: 09/01/94 EDN-Design Ideas

Two Signals Easily Control Tricolor LED: 09/14/95 EDN-Design Ideas

Two Transistor LED Flasher #1:

Two Transistor LED Flasher #2:

Voltage to current converter drives white LEDs: 06/27/2002  EDN - Design Ideas / You sometimes need to drive a white LED from one 1.5V battery. Unfortunately, the forward voltage of a white LED is 3 to 4V. So, you would need a dc/dc converter to drive the LED from one battery. Using the simple circuit in Figure 1, you can drive one white LED or two series-connected green LEDs, using only a few components.

White LED drive from 1.5V: Blocking oscillator based design allows LED + power supply to fit in #222 lamp base.

White LED driver touts high efficiency: 06/12/03  EDN-Design Ideas / White LEDs, the most recent addition to the LCD backlight, find common use in providing backlight for color LCDs. Thanks to their size and white-light output, they appear in small, portable devices with color displays, such as PDAs and cellular phones. Like other LEDs, a white LED needs a constant-current source—typically, on the order of 15 to 20 mA.

White LED Flashlight:


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