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Indicator Circuits
Indicators:  #'s - A       B - C       D - F       G - I       J - L       M - P        R - S       T - Z
Last Updated on: Tuesday, November 21, 2017 05:47 AM

Circuits Designed by Dave Johnson, P.E. :

Ramping Lamp DriverThis circuit drives any 12v lamp, incandescent or LED type, in a ramping fashion.  Each press of the button toggles the lamp from a fully off mode to a fully on mode.  But, instead of an instantaneous lamp intensity change, the power is slowly ramped up a . . . Hobby Circuit designed by David Johnson P.E.-December, 2007

Remote LED Indicator LightThere are times when you would like to transmit a signal from one LED indicator light to second LED at another location.  The circuit below works well for this application.  It takes advantage of the fact that the internal infrared LED inside an opto-isolator. . . Circuit by David A. Johnson P.E.-December, 2008

RFID Smart Key DetectorThe hobby circuit below was designed to indicate if a key held over the small coil of wire contains a 125KHz RFID chip.  These chips are often used in smart car ignition keys.  The left side circuit forms a 125KHz power oscillator, which drives the 680uH a . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

RS232 Data Bus Status MonitorI designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volt. . . Circuit by David A. Johnson P.E.-December, 2007

RS-232 Serial Interface Status Indicator CircuitI designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights . . . Hobby Circuit designed by David Johnson P.E.-December, 2007

Self Powered AC IndicatorOften there is a need to monitor when AC current flows into a load.  The circuit below works well for this application.  It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser.  A wire carrying the AC current is . . . Hobby Circuit designed by Dave Johnson P.E.-December, 2007

Self-Powered AC Current IndicatorOften there is a need to monitor when AC current flows into a load.  The circuit below works well for this application.  It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser.  A wire carrying the AC current is. . . Circuit by Dave Johnson P.E.-December, 2007

Serial Data Bus Status MonitorI designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volt. . . Circuit by Dave Johnson P.E.-December, 2007


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Rainbow LED indicates voltage with color -  7-Dec-04 EDN-Design Ideas Meters that indicate analog levels via a moving-pointer meter, a numeric display, or a column of LEDs typically occupy considerable panel area and requirethan a casual glance to read.  An indicator lamp or LED takes little space but indicates only an on or off condition.  However, an unobtrusive LED that changes color as a function of a measured value would enable an observer to easily asse __ Circuit Design by David Prutchi, Impulse Dynamics, Haifa, Israel

Ramping Lamp Driver -  This circuit drives any 12v lamp, incandescent or LED type, in a ramping fashion.  Each press of the button toggles the lamp from a fully off mode to a fully on mode.  But, instead of an instantaneous lamp intensity change, the power is slowly ramped up a . . . Hobby Circuit designed by David Johnson P.E.-December, 2007

Remote Audio Level Indicator -  The normal level-indicator circuits which are available in the market require connections to be made to the output of the player, which may not be easily accessible.  The audio level indicator circuit described here removes this restriction as it may be placed close to the playerís speakers and yet the desired effect can be __ Designed by Popescu Marian

Remote Doorbell Warning Switch -  This circuit should only be used with the solenoid type chime doorbells, the electronic type that play tunes will not work here.  The hardest part for this circuit was the title.  It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication, i.  e.  a lamp __ Designed by Andy Collison

Remote LED Indicator Light -  There are times when you would like to transmit a signal from one LED indicator light to second LED at another location.  The circuit below works well for this application.  It takes advantage of the fact that the internal infrared LED inside an opto-isolator. . . Circuit by David A. Johnson P.E.-December, 2008

RFID Smart Key Detector -  The hobby circuit below was designed to indicate if a key held over the small coil of wire contains a 125KHz RFID chip.  These chips are often used in smart car ignition keys.  The left side circuit forms a 125KHz power oscillator, which drives the 680uH a . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Ringing Phone Light Flasher -  This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop.  Here is such a device.  The ring detect part of this circuit came from [url]http://www.  hut.  fi/Misc/Electronics/circuits/telephone_ringer.  html[/url].  Notes: 1.  You may need to use a lower voltage zener for D1 and D2.2.  You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly.3.  Be very sure that you have not accidentally connected 120V to the phone line when building and installing this __ Designed by Aaron Cake

RS232 Data Bus Status Monitor -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volt. . . Circuit by David A. Johnson P.E.-December, 2007

RS-232 Serial Interface Status Indicator Circuit -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights . . . Hobby Circuit designed by David Johnson P.E.-December, 2007

Self-Powered AC Current Indicator -  Often there is a need to monitor when AC current flows into a load.  The circuit below works well for this application.  It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser.  A wire carrying the AC current is. . . Circuit by Dave Johnson P.E.-December, 2007

Serial Data Bus Status Monitor -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volt. . . Circuit by Dave Johnson P.E.-December, 2007

Simple  Stereo Level Indicator -  Usually, low-priced home stereo power amplifiers donít have output level indicators.  An output power level indicator can be added to each channel of these stereo power amplifiers.  As low levels of...__ Electronics Projects for You

Simple  Water Temperature Indicator -  When bathing a baby, itís important that the water is neither too cold nor too hot.  You test the water by dipping your fingers in the bath tub before putting the...__ Electronics Projects for You

Simple Circuit Battery-Status Indicator Uses Two LEDs -  08/12/10 EDN-Design Ideas Use LED brightness to indicate battery charge.    __ Circuit Design by Abhijeet Deshpande, Peopleís Education Society Institute of Technology, Bangalore, India

Simple Circuit Blown-Fuse Indicator Sounds an Alarm -  10-Jul-08 EDN-Design Ideas A simple blown-fuse-indicator circuit sounds a buzzer and flashes an LED when a fuse blows __ Circuit Design by Vladimir Oleynik, Moscow, Russia

Simple Circuit Detects Current Pulse -  01/06/94 EDN-Design Ideas The pulse detector provIdeas a visible indication of positive and negative current pulses.  The pulses amplitudes can vary from20 to150 mA.  The pulses durations can range from10 to40 msec, and their repetition rate can span40 to180 pulses/minute __ Circuit Design by Richard McGillivray, Grey Bruce Regional Health Centre, Owen Sound, Ontario, Canada

Simple Circuit forms peak/clipping indicator -  11/22/01 EDN-Design Ideas The simple peak detector in Figure 1 is the result of a need for a single-5V-supply, level/clipping indicator for a multimedia-PC sound system.  The design is unique in that it detects both stereo channels on a single peak-hold capacitor.  All the adjustments in the circuit simultaneously apply to both left and right stereo inputs __ Circuit Design by Steven Hageman, Agilent Technologies, Santa Rosa, CA

Simple Circuit indicates a low battery -  02/03/14EDN-Design Ideas It may seem a bit counterintuitive to power on an LED when a battery is already low, but this Design Idea does it with aplomb __ Circuit Design by James Wood

Simple Circuit Indicates Health of Lithium-Ion Batteries -  05/14/09  EDN-Design Ideas A simple inexpensive circuit quickly indicates a battery pack's health __ Circuit Design by Fritz Weld, Friedberg, Germany

Simple Circuit Moisture indicator -  No circuit description, schematic only__ CdS Electronic

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.    __ Circuit Design by Jim Hagerman, Hagerman Technology, San Diego, CA

Solar Battery Charging Indicator -  T.K.  HAREENDRANHere is the circuit of a simple charging monitor that indicates whether the storage battery of a solar power unit is being charged or not.  It, however, does not tell...__ Electronics Projects for You

Sound Level Indicator -  This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range. The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low sound levels but it increases its range 20dB for loud sounds. __ Designed by Audioguru

Sound Level Indicator -  This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range.  The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low __ Designed by Audioguru

Sound to Light -  This circuit gives out a short pulse each time the 220v supply passes through zero.   __ Designed by © David Hoult

Stabilised Power Supply with Short-Circuit Indication -  Here is an efficient 4-stage stabilised power supply unit for testing electronic circuits.  It provides well regulated and stabilised output, which is essential for most electronic circuits to give proper results....__ Electronics Projects for You

Status Indicator Flags Five Discharge States -  01/20/94 EDN-Design Ideas The circuit actually indicates five conditions of the battery.  A steady glow assures the user that the battery is strong and healthy.  A2-Hz brief flicker off indicates that the battery is starting to show age.  A more insistent,50%,5-Hz flashing is a warning to have a spare battery on hand.  A brief flicker __ Circuit Design by Glen Chenier, Fitel Photomatrix, Nepean, ON, Canada


Indicator Circuits
Indicators:  #'s - A       B - C       D - F       G - I       J - L       M - P        R - S       T - Z


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