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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, October 24, 2017 02:55 PM


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

Circuits Designed by Dave Johnson, P.E. :

Bad Light Bulb Indicator This request came from a Discover Circuits visitor.  He wanted to turn on a LED indicator light whenever a circuit detected a burned out tail/brake light on a car or truck.  The circuit shown below uses a transistor switch, to detect current flowing through a low value resistor. . . Circuit by David A. Johnson P.E.-December, 2006

Battery Charge Current Indicator This circuit turns on a LED whenever it detects at least 25ma of battery charge current. . . Circuit by David A. Johnson P.E.-July, 2006

Beeper indicates Check Engine When driving down a busy road, you may not notice a “check engine” indicator light that suddenly turns on within the car’s instrument panel.  You could drive for many miles before noticing the light.  To provide an audible indication of trouble, the hobby . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Bidirectional DC Current Indicator This circuit is handy for battery powered systems.  The circuit is self-powered using a single 3v lithium coin cell.  The current draw is so low that the battery should last for years.  The hobby circuit flashes a red LED when DC current is drawn from the battery and flashes a green LED whenever current flows into the battery.  Two “probe” input wires connect across a section of cable, which acts as a shunt resistor.  A voltage of only 5mv in either direction will trigger a LED indication . . . Hobby Circuit designed by David Johnson P.E.-March, 2011

Call-for-Service Beeper  This device functions like a lobby desk service request bell.  A short beep is sounded whenever the large pushbutton on top of the device is pressed.  Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . Hobby Circuit designed by David A. Johnson P.E.-September, 2005

Check Engine Beeper  When driving down a busy road, you may not notice a “check engine” indicator light that suddenly turns on within the car’s instrument panel.  You could drive for many miles before noticing the light.  To provide an audible indication of trouble, the hobby . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Chicken Coop Door Opener with Timer  I received an email from a guy in Australia who was trying to build a chicken coop system.  He was planning on using a conventional garage door mechanism to open and close the 6 doors to the coop.  The commercial door opener opened and closed the doors with a single pushbutton.  He wanted to install a standard 220vac powered timer so he could open the doors in the morning and close them at night. . . Circuit by David A. Johnson P.E.-March, 2013

Circuit Indicates Battery Charge Current  This circuit was inspired by a company needing a DC current indicator light which was small enough to be molded into a medium size 28v rechargeable battery assembly.  They specified that they wanted the circuit to turn on the LED indicator light with 500ma or more of battery charge current . . . Hobby Circuit designed by David Johnson P.E.-January, 2011

Circuit Monitors 12v Lamp Current  - This circuit monitors DC current and turns on a LED indictor light whenever DC current flows into a 12v lamp . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Classic Plus & Minus DC Power Supply  This is a classic example of a regulated DC power supply that produces both a positive 15v and a negative 15v from a 20vac wall adapter. . . Circuit by David Johnson P.E.-October, 2005

Clear Fluid Detector #2  Using an ultra low power technique, this circuit detects when a clear fluid is inside a piece of clear plastic tubing.  It can be used for fluid level control and monitoring. . . Circuit by Dave Johnson P.E.-October, 2005

CMOS IC Flashes LED  Judging from the numerous references I have received, this electronic circuit, hobby circuit seems to be rather popular.  Many published circuits which flash LEDs need 3 or more volts.  This electronic circuit uses only a single inexpensive C-MOS IC and . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Current Indicator for Battery Chargers  This circuit was inspired by a company needing a DC current indicator light which was small enough to be molded into a medium size 28v rechargeable battery assembly.  They specified that they wanted the circuit to turn on the LED indicator light with 500ma or more of battery charge current. . . Circuit by Dave Johnson P.E.-January, 2011


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

Bad Light Bulb Indicator -  This request came from a Discover Circuits visitor.  He wanted to turn on a LED indicator light whenever a circuit detected a burned out tail/brake light on a car or truck.  The circuit shown below uses a transistor switch, to detect current flowing through a low value resistor. . . Circuit by David A. Johnson P.E.-December, 2006

Battery Charge Current Indicator -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current. . . Circuit by David A. Johnson P.E.-July, 2006

Battery Charger Indicates Rate of Charge -  05/25/95 EDN-Design Ideas A single LED indicates wher  battery Chargers s delivering a trickle charge or a fast charge, Circuit designed to charge2-14 cells.    __ Circuit Design by Larry Suppan, Maxim Integrated Products, Sunnyvale, CA

Battery Equal Charge Indicator -  The circuit below illuminates an LED to indicate unequal charges between two 12 volt lead batteries.  It can be used to verify that two batteries are connected in parallel or isolated since the LED will be off when the voltages are equal within a tollerance, or on if the voltage difference is greater than 100 millivolts.  Three comparators __ Designed by Bill Bowden

Battery Low indicator -  This is a page with a few circuits which may be useful for monitoring the state of your batteries.   __ Designed by Richard Torrens

Battery Monitor Emulates Auto Dashboard -  07/03/97 EDN-Design Ideas  When you use battery-powered scientific-recording equipment, you must know the state of the battery, because an unnoticed battery run-down can lead to loss of data.  Several types of warning indicators are available, but all have their drawbacks.  Moving-coil indicators, test terminals, and digital flags, for example, __ Circuit Design by TG Barnett and J Millar, University of London, UK

Battery Monitor for 12V Lead-Acid -  This simple circuit makes it posible to monitor the charging process to a higher level.  If you need more information then check out the LM3914 Datasheet. 
Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy __ Designed by Jan Hamer

Battery-Level Indicator -  Normally, in mobile phones, the battery level is shown in dot or bar form.  This lets you easily recognise the battery level.  Here we present a circuit that lets you know...__ Electronics Projects for You

Battery-Low Indicator -  Rechargeable batteries should not be discharged below a certain voltage level.  This lower voltage limit depends upon the type of the battery.  This simple circuit can be used for 12V batteries...__ Electronics Projects for You

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

Bed levelling for 3D printer -  EDN-Design Ideas 03/19/2014     3rd prize winner in the TI LDC1000 design contest.   One of the challenges to consumer 3d printing involves leveling the print platform.  Current methods    (insert a business card or piece of paper and adjust screws until it "just fits") lack precision.  Many "air prints" and much frustration result from poorly adjusted print platforms.  I propose building a device that can be placed on the rails and used to measure the platform to print head height at each adjustment point.  This would eliminate the guesswork in bed leveling.   __ Circuit Design by Michael Rigsby

Beeper indicates Check Engine -  When driving down a busy road, you may not notice a “check engine” indicator light that suddenly turns on within the car’s instrument panel.  You could drive for many miles before noticing the light.  To provide an audible indication of trouble, the hobby . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Bicolor LED Indicates 10 States -  03/03/11  EDN-Design Ideas Most microcontroller-based devices have several states of operation.  Pushbutton switches often control these states.  To minimize costs, many designs use only one switch; the number of presses sets the microcontroller’s state.  In the circuit in this Design __ Circuit Design by Abel Raynus, Armatron International, Malden, MA

Bi-Color LED Indicates Power/Fault -  Single LED indicates both power on and blown-fuse conditions.   __ Designed by Jim Haggerman, Hagerman Technology LLC

Bicycle Indicator -  The electronic bicycle signaling unit described here uses low-cost components and is a good substitute to many commercially available versions.  It works in an extremely different manner and is convenient to...__ Electronics Projects for You

Bidirectional DC Current Indicator -  This circuit is handy for battery powered systems.  The circuit is self-powered using a single 3v lithium coin cell.  The current draw is so low that the battery should last for years.  The hobby circuit flashes a red LED when DC current is drawn from the battery and flashes a green LED whenever current flows into the battery.  Two “probe” input wires connect across a section of cable, which acts as a shunt resistor.  A voltage of only 5mv in either direction will trigger a LED indication . . . Hobby Circuit designed by David Johnson P.E.-March, 2011

Blown Fuse Indicator -  This blown fuse indicator will work with a wide range of DC supply voltages from 5V to 50V.  It illuminates LED1 when the fuse blows.  With the fuse intact, Q1 is held off and there is no bias current available for the base of Q2.  So the LED is off.  When the fuse blows, a

Blown Fuse Indicator -  Generally, when an equipment indicates no power, the cause may be just a blown fuse.  Here is a circuit that shows the condition of fuse through LEDs.  This compact circuit is...__ Electronics Projects for You

Blown Fuse Indicator -  a simple way to see if a fuse has blown without removing it from its holder __ Designed by Andy Collison

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

Brake Failure Indicator -  Do you want to get an early warning of brake failure while driving? Here is a brake failure indicator circuit that constantly monitors the condition of the brake and gives an...__ Electronics Projects for You

Broken-Coil Detector Is Simple Circuit Yet Robust -  03/04/10  EDN-Design Ideas The circuit in this Design Idea was originally designed to detect damaged conveyor belts in the mining industry.  Thin coils are embedded in the conveyor belt.  If the belt suffers damage, it stretches at the affected location, causing one or more coils to break.  The method for detecting the broken coil is to allow a “sensing” coil to magnetically couple with the passing coils in the belt, thus changing the total inductance of the magnetic pair.  The sensing coil is part of an LC oscillator    (Figure 1) .   __ Circuit Design by Juan Pablo Caram, Santiago, Chile

Broken-Coil Detector Is Simple Circuit Yet Robust -  03/04/10  EDN-Design Ideas The circuit in this Design Idea was originally designed to detect damaged conveyor belts in the mining industry.  Thin coils are embedded in the conveyor belt.  If the belt suffers damage, it stretches at the affected location, causing one or more coils to break.  The method for detecting the broken coil is to allow a “sensing” coil to magnetically couple with the passing coils in the belt, thus changing the total inductance of the magnetic pair.  The sensing coil is part of an LC oscillator    (Figure 1) .   __ Circuit Design by Juan Pablo Caram, Santiago, Chile

Call Bell with Welcome Indication -  Here is a simple call bell circuit that displays a welcome message when somebody presses the call bell switch momentarily.  The alphanumeric display can be fitted near the call bell switch.__ Electronics Projects for You

Call-for-Service Beeper -  This device functions like a lobby desk service request bell.  A short beep is sounded whenever the large pushbutton on top of the device is pressed.  Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . Hobby Circuit designed by David A. Johnson P.E.-September, 2005

Car Battery Indicator -  Text is not English __ Designed by Smartkit

Cellular Phone calling Detector -  Flashes a LED when detecting an incoming call; Powered by one 1.5V cell __ Contact: Flavio Dellepiane, fladello @ tin.it

Charge indicator gauges lead-acid batteries -  05/27/99 EDN-Design Ideas Although rechargeable, sealed lead-acid cells are uncommon in portable  applications, they are a good choice for standby applications, such as emergency lighting and burglar alarms.  A key advantagePDF has several circuits, please scroll to find this one.    __ Circuit Design by Fran Hoffart, Linear Technology Corp, Milpitas, CA

Charging Time Indicates Capacitor Value -  08/11/11  EDN-Design Ideas A comparator changes state when capacitor voltages are equal during rise and fall, which triggers a time measurement.   A recent research project using a capacitive sensor to measure water levels comprises two PCB  (printed-circuit-board) plates placed one in front of the other at a controlled distance.  Every plate divIdeas into eight equal copper zones, resulting in eight equivalent parallel-plate capacitors  (Figure 1) .  Every capacitor has a plate area of 25 cm2.  To measure the water’s total height, the project uses a special hydro-insulated layer to avoid short circuits.  Knowing the layer thickness and the electrical permittivity of the hydro-insulated substance allows you to express the distance between every two plates and the dielectric’s electrical permittivity. __ Circuit Design by Vlad Bande and Ioan Ciascai, Technical University of Cluj-Napoca, Cluj-Napoca, Romania

Check Engine Beeper -  When driving down a busy road, you may not notice a “check engine” indicator light that suddenly turns on within the car’s instrument panel.  You could drive for many miles before noticing the light.  To provide an audible indication of trouble, the hobby . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Chicken Coop Door Opener with Timer -  I received an email from a guy in Australia who was trying to build a chicken coop system.  He was planning on using a conventional garage door mechanism to open and close the 6 doors to the coop.  The commercial door opener opened and closed the doors with a single pushbutton.  He wanted to install a standard 220vac powered timer so he could open the doors in the morning and close them at night. . . Circuit by David A. Johnson P.E.-March, 2013

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

Circuit forms low-frequency circulator -  10/11/01 EDN-Design Ideas The electronic circulator made its debut ten years ago (Reference 1].  It functioned at VHF as a three-port unit using a Comlinear (now part of National Semiconductor, www.nsc.com] CLC 406 operational amplifier.  The circuit in Figure 1 extends the circulator's performance to four-port operation at low frequencies, using the readily available 941 (equivalent to the ubiquitous 741] and LM3 __ Circuit Design by Richard Kurzrok, Queens Village, NY

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

Circuit Indicates Ac-Mains-Fuse Failure -  8-Jan-09 EDN-Design Ideas Use this circuit to alert you when a fuse fails __ Circuit Design by Vladimir Oleynik, Moscow, Russia

Circuit Indicates Battery Charge Current -  This circuit was inspired by a company needing a DC current indicator light which was small enough to be molded into a medium size 28v rechargeable battery assembly.  They specified that they wanted the circuit to turn on the LED indicator light with 500ma or more of battery charge current . . . Hobby Circuit designed by David Johnson P.E.-January, 2011

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

Circuit Monitors 12v Lamp Current  -  This circuit monitors DC current and turns on a LED indictor light whenever DC current flows into a 12v lamp . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Classic Plus & Minus DC Power Supply -  This is a classic example of a regulated DC power supply that produces both a positive 15v and a negative 15v from a 20vac wall adapter. . . Circuit by David Johnson P.E.-October, 2005

Clear Fluid Detector #2 -  Using an ultra low power technique, this circuit detects when a clear fluid is inside a piece of clear plastic tubing.  It can be used for fluid level control and monitoring. . . Circuit by Dave Johnson P.E.-October, 2005

CMOS IC Flashes LED -  Judging from the numerous references I have received, this electronic circuit, hobby circuit seems to be rather popular.  Many published circuits which flash LEDs need 3 or more volts.  This electronic circuit uses only a single inexpensive C-MOS IC and . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Contactless Tachometer on AVR. Part 1. Schematic -  This new contactless tachometeris the device based on an ATMEGA48 AVR micro controller from Atmel, and is able to measure very high RPMs, as well as very low ones.  It is based on an IR  (Infra Red) opto-couple to detect shaft rotation.  Principle__ Radio Locman

Current Indicator for Battery Chargers -  This circuit was inspired by a company needing a DC current indicator light which was small enough to be molded into a medium size 28v rechargeable battery assembly.  They specified that they wanted the circuit to turn on the LED indicator light with 500ma or more of battery charge current. . . Circuit by Dave Johnson P.E.-January, 2011

Cut Phone Line Detector -  A while ago I got an email asking for the schematic of a circuit to detect cut phone lines.  It didn't take me long to find this circuit in Electronics Now.  When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc.  It can also be connected to a security system __ Designed by Aaron Cake

Cut Phone Line Detector -  This circuit speaks for itself.    When the phone line is okay, Q1 acts as a short with a very high ohms value via R1, R2, and R3 for a total of about 66 MegOhm so very high.  When the phone line is cut  (Tony van Roon's open) , it activates the MOSFET  (Tony van Roon's Q3) via transistor Q2 to drive the load.    Substitutes are fine, none of the components are critical __ Designed by Tony van Roon  VA3AVR


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

 


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