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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

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LED Circuits
LED Circuits designed by David Johnson, PE:
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0.5v Negative Supply  -  Although not very efficient, this simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op Amp circuits, . . . [Circuit by Dave Johnson P.E.,  07/13/06]


1 Line Telephone Line Status Indicator  -  This circuit monitors one phone line . . . [Circuit by Dave Johnson P.E.,  06/10/00]


1.5v LED Flasher Version A  -  Many published circuits that flash LEDs need 3 volts or more.  This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5 volt AA alkaline battery cell. The circuit uses a charge pump technique to provide . . . [Circuit by David A. Johnson P.E.,  06/04/00]


10 LED Sequential Flasher using Low Powr  -  A while back I posted a flasher circuit which flashed 10 LEDs sequentially.  That circuit was powered by four AA alkaline cells.  The circuit below operates much the same way but has been modified to run from a single 3v CR2032 lithium coin cell . . . [Circuit by David A. Johnson P.E.,  04/17/11]

120 VAC / 240 VAC Indicator  -  Two LEDs indicate if a power line has 120vac or 240vac voltage on it . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/09/06]


1-Nimh Cell powers White LED  -  There are a lot of white LED driver circuits floating around.  A popular circuit called the “Joule Thief” can drive one white LED from a single 1.2v or 1.5v battery cell.  Most of these circuits use one or two transistors to form a voltage boost circuit . . . [Hobby Circuit designed by David Johnson P.E.,  09/26/09]


1us LED Pulse Driver + Voltage to Frequency Converter  -  This circuit receives the signal from the above Amplifier and launches powerful 1uS infrared light pulses from a low cost LED that are frequency modulated by the audio information. The 10KHz center frequency of the pulse stream is low enough so a standard . . . [Hobby Circuit designed by Dave Johnson P.E.,  03/22/99]


1W White LED Night Light  -  As many of you know, I have a pet peeve with poorly made LED night lights.  Often, the light from the LED quickly fades, so within months, the light is useless.  I have posted several versions of modified night lights using higher quality components.  This circuit is yet another version, which produces much more light than those other designs. . . . [Hobby Circuit designed by David A. Johnson P.E.,  11/06/08]


24 Volts AC to 24 Volts DC Power Supply  -  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 . . . [Hobby Circuit designed by David Johnson P.E.,  02/20/11]


24V DC Powered Beeper with 4 Separate Inputs  -  24vac is a popular voltage.  It is often used in low voltage lighting systems and industrial controls.  It is much less dangerous than 120vac/240vac line voltages.  This hobby circuit below is one method to efficiently power a cluster of 7 white LEDs from 24vac. . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/19/09]


3 Minute LED Closet Light  -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuit’s standby current . . . [Hobby Circuit designed by David A. Johnson P.E.,  11/14/10]


30 LED Night Light  -  This Hobby Circuit uses a capacitor to limit the current through a series-parallel string of 30 LEDs. 15 LEDs are wired in series in one direction and 15 more in the other direction. The capacitor limits the average current to about 20ma. The 100 ohm metal oxide resistor acts as a fuse.   . . . [Hobby Circuit designed by David A. Johnson P.E.,  10/27/05]


3-Minute Closet Light  -  I have a coat closet by my front door.  The thing is very dark at night and really needs some kind of illumination inside.  I could hire an electrician to install a light in the closet ceiling and then wire it to a toggle switch outside the door but that would cost me quite a bit of money . . . [Circuit by Dave Johnson P.E.,  12/25/11]


3-Minute Closet Light #2  -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuit’s standby current is only a few microamps.  A set of fresh batteries should last at least 200 light applications.  The circuit uses a Schmitt trigger inverter and two transistors.  When the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged . . . [Circuit by David A. Johnson P.E.,  11/14/10]


3v Battery Powered White LED Driver  -  The circuit below will drive any LED color, including white LEDs, using a DC power supply ranging from 2v to 3.3v.  White and blue LEDs normally require over 3v, so the circuit below uses a charge pump scheme to deliver a constant LED light intensity . . . [Circuit by David Johnson P.E.,  08/15/10]


3v Powered Super Bright LED Flasher  -  I have posted several kinds of LED flashers over the years. This is yet one more flasher, designed to flash any high power LED of any color.  It hits the LED with a 25ms 250ma pulse once every 2 seconds. This works out to an average current about 3ma.  It . . . [Hobby Circuit designed by Dave Johnson P.E.,  04/22/09]


3v Universal LED Flasher  -  This low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts.  The 1.0Hz 10ms LED pulsed current is held to a constant 10ma . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/11/06]


4 to 20ma Current Loop Senses Temperature  -  I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/04/00]


9v Battery Voltage Monitor  -  This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts.  It uses a LTC1440 comparator, which also contains a 1.18v reference diode.  In standby mode, the circuit draws only 4uA . . . [Circuit by Dave Johnson P.E.,  07/09/06]


LED Circuits designed by David Johnson, PE:
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