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Pot
Controlled Variable LED Intensity Circuit - The circuit below uses power from four rechargeable AA
NiMH cells to drive 3 white LEDs. A potentiometer varies the duty cycle of a pulse width modulator circuit to
vary the intensity of the LEDs from 0% to 100%. The beauty of the circuit is that when the . . . [Circuit by Dave
Johnson P.E., 09/27/09]
POV Persistence of Vision 2 x
32 LED display - . . .
Power 220V Flashing LED -
AC mains operated single LED flasher circuit, built using the popular CMOS timer chip TLC555 is shown below. The
whole circuit is powered directly by the grid supply of 230VAC through a capacitive potential divider and
associated components. This minuscule Power LED Flashing circuit can be easily fit inside a very small. . .
[Circuit Posted by T.K. Hareendran]
Power An LED Driver Using
Off-The-Shelf Components - 01/20/11 EDN Design Idea Drive LEDs with a 555 timer and two
transistors. . . [by TA Babu, Chennai, India
Power OK LED for PC -
Simple, low cost three transistor circuit lights LED only if all four PC power supply voltages +/-5V, +/-12V) are
present. . . . [Jim Haggerman, Hagerman Technology LLC]
Power
Supply-24 Volts AC to 24 Volts DC - The idea for the circuit below came from a company needing to
power several 24v DC LED assemblies from an existing 24vac supply. They did not need a rock solid and regulated
24 volts but a voltage which hovered around that voltage. Running the AC through . . . [Circuit by David A.
Johnson P.E., 02/20/11]
Powering LEDs costs mere
pennies 33 - Lately the hoopla concerning LED lighting has been overwhelming. Everyone claims this
costs mere pennies to power. I decided to put a new twist on a classic science experiment to prove that LEDs do
cost pennies to power. Literally. . . .
Powers LED with Constant
Current Starting at 100MV over VF - This is a proof of concept circuit which needs improvement. The
part values shown will run a high efficiency red LED with a Vf of 1. 9V from only 2 NiCads, right down to 2
volts. For a white LED you will need more batteries and you must increase the 1. 0K resistor to a higher value.
Current sensing at a. . . [Circuit by Stepan Novotill]
Power-supply IC drives multiple
LEDs - 09/02/04 EDN Design Idea Bright LEDs are becoming prominent sources of light. They often
have better efficiency and reliability than do conventional light sources. Although LEDs can operate from an
energy source as simple as a battery and a resistor,. . . [by John Lo Giudice and Vee Shing Wong,
STMicroelectronics, Schaumburg, IL]
Processor's PWM output controls
LCD/LED driver - 05/27/04 EDN Design Idea The PWM (pulse-width-modulation] output available from
many microprocessors is based on an internal 8- or 16-bit counter and features a programmable duty cycle. It is
suitable for adjusting the output of an LCD driver (Figure 1) , a n. . . [by Joe Neubauer, Maxim Integrated
Products, Sunnyvale, CA]
Programmable LED -
Alex Inspired by various LED Throwies, blinking LEDs and similar instructables I wanted to do my version of an
LED controlled by a microcontroller. The idea is to make the LED blinking sequence reprogrammable. This
reprogramming can be done with. . .
Programmable LED Flashers -
LED goes to steady state after a preset number of flashes; Two simple, wide supply range operating circuits. . .
[Flavio Dellepiane's web site]
Programming Fun Lights With
TI's TCA6507 - LED lighting designers are challenged with meeting their efficiency and reliability
goals faster in advanced LED lighting designs. LED lighting customers seeking the latest in innovative and
affordable LED lighting solutions can benefit from TI's broad product portfolio of LED drivers, AC/DC, DC/DC,
power management devices, wireless and wired interface control and embedded processors. LED designers have the
option of not only controlling the power stage, but regulating LED currents as well, eliminating the need for
multiple components and reducing system cost. . . . [Texas Instruments App Notes, 30-Nov-07]
Propeller Message Display with
Temperature Indicator - Here we describe a microcontroller-based propeller display that displays any
message sent to it via hyper-terminal of a personal computer. Moreover, a temperature sensing IC (TMP125) is
mounted onto the propeller display to display temperature in real time. It gives a 360-degree view and displays
several characters in a revolving circular path using just eight LEDs. The main highlight o this project is a
vertical facing display with true 360-degree viewing angle. . . . [© EFY Enterprises Pvt. Ltd. All rights
reserved]
Propellor clock PIC16F84 -
A few light emitting diodes spin, precisely controlled by a PIC microprocessor, giving the illusion of a larger
array. . . . [Bob Blick's design]
Protect Power-LED Strings from
Overcurrent - 06/23/11 EDN Design Idea Add diodes and a transistor to a current mirror to prevent
LED damage. A common method for driving multiple power LEDs is through two parallel strings. This inexpensive and
less critical driver circuit can provide a lower voltage. However, the driver circuit must deliver twice the
current of other methods and needs a circuit that halves the current in the two strings, regardless of the LEDs’
forward voltages. The LEDs’ forward-voltage tolerance is as high as 20%, and the voltages change with LED
temperature and aging. . . [by Luca Bruno, ITIS Hensemberger Monza, Lissone, Italy]
Provide High-Side
Current-Sensing for White-LED Drivers - 02/19/04 EDN Design Idea White LEDs find wide use in
backlighting color-LCD screens in most portable devices, such as cellular phones, PDAs, and MP3 players. Multiple
LEDs often connect in series to ensure that the same current flows through every LED. To . . . [by Dimitry Goder,
Sipex Corp, San Jose, CA]
Pulsed LED A High Current
Circuit - Just to Play with, But it Might have some Practical Applications. . . . [G.L. Chemelec,
designer]
Pulsed LED
Test Circuit - This circuit is designed to test visible and infrared LEDs in pulsed mode operations.
It can drive the LED with peak currents in excess of 10 Amps. A light detector nearby can monitor the response
time and intensity of the LED under test . . . [Circuit by David A. Johnson P.E., 06/17/00]
Pulsed LEDA High Current
Circuit - Just to Play withBut it Might have some Practical Applications. . . [G.L. Chemelec,
designer]
Pushbutton
Controlled Up/Down Ramping Light - There are times when you want a lamp to gradually change from dark
to light and from light to dark, with each push of a pushbutton switch. The circuit below performs this control
function using a flip/flop and a classic pulse width modulation or PWM . . . [Circuit by Dave Johnson P.E.,
03/22/09]
PV Solar Cell
Test Fixture - This is an illustration of a test fixture, which can be used to test individual solar
cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be tested
under constant light level conditions . . . [Hobby Circuit designed by David Johnson P.E., 10/01/06]
PWM controller drives LEDs from
high-voltage lines - 03/04/04 EDN Design Idea Powering LEDs from a wide dc range—say, 30 to
380V—without wasting a lot of power in the regulating block, is a difficult task when the LED current needs to be
constant. Dedicated LED drivers are available, but they usually implement. . . [by Christophe Basso, On
Semiconductor, Toulouse, France]
Quad DC/DC Converter for Triple
Output TFT Supply Plus LED Driver - LT1942. . . [Linear Technology]
Quiz - This project
can be used for a quiz with up to 4 contestants (or teams). Each contestant has a trigger push-switch and LED.
When a trigger switch is pressed it lights the corresponding LED, sounds the bleeper and prevents the other
trigger switches from working - therefore showing which contestant was the first to press their switch. . .
[Designed by John Hewes]
Radio Tower
Lamp Monitor - The circuit below uses two 3 Amp diodes to produce a fairly constant 2 volts whenever
current is routed to the tower lamp. The voltage is used to power a bright LED. The LED will only turn on when
current is actually flowing to the lamp. With the component values shown, the circuit will work with lamps
ranging from 40 to 250 watts. . . . [Hobby Circuit designed by David Johnson P.E., 07/18/06]
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