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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

Circuits Designed by Dave Johnson, P.E. :

Telephone Status Indicator for 4 LinesMany home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Three-Volt Low Battery Voltage FlasherMany battery powered devices use two AA alkaline cells.  Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating.  The hobby circuit below can be connected to a 3v battery, to give you some . . . Hobby Circuit designed by Dave Johnson P.E.-January, 1998

Transmit to a Remote LED Indictor 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 . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2008

Two Line Telephone Line Status IndicatorMany home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation.  The circuit is line polarity insensitive . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Two Transistor OscillatorsThis page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro amp of current. . . Circuit by David Johnson P.E.-December, 2002

Two-Transistor Low Power OscillatorsThis page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro amp of current . . . Hobby Circuit designed by Dave Johnson P.E.-December, 2002

Ultra Low Power Detects Clear FluidUsing 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 . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2005

Version 4 of a DC Current IndicatorThe circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005

Version a of 1.5v LED FlasherTo squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency.  A small 1.5 volt alkaline N cell should flash the LED for a full year.  It too uses a "charge pump" technique to provide a LED the needed voltage. . . Circuit by David Johnson P.E.-June, 2000

Water Flowing in Pipe IndicatorThe vibrations associated with water flowing through a pipe are picked up by an inexpensive piezoelectric wafer.    The signal from the wafer is first boosted by a micropower transistor amplifier and then fed to an ultra low power voltage comparator.     When the vibration signal has sufficient amplitude, a FET transistor switch is activated…[Circuit designed by Dave Johnson P.  E.  , 6/06/2009]. . . Circuit by David Johnson P.E.-July, 2009

Wireless LED FlasherThere are times when you would like to flash a LED through a thick plastic case without wires.  The circuit below performs this feat.  It can be powered from a supply ranging from 3v to 6v.  It draws about 300ua of average current at 5v. . . Circuit by David A. Johnson P.E.-January, 2011

Wireless 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 David Johnson P.E.-July, 2006


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

Telephone Headgear -  A compact, inexpensive and low component count telecom headset can be constructed using two readily available transistors and a few other electronic components.  Since the circuit draws very little current, it is ideal for parallel operation with electronic Telephone set __

Telephone In Use Indicator -  This circuit will illuminate a LED if one of your telephones is in use.  It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC.   __ Designed by Miroslav Adzic

Telephone in Use LED Indicator -  Circuit to illuminate an LED when any telephone extension is off the hook.   __ Designed by Bill Bowden

Telephone Lamp -  Here is a White LED Lamp that turns on when the telephone rings.  The cool white light helps to locate the phone in darkness and also helps to note the message or telephone number.  The lamp remains on for three minutes then turns off.  The telephone lamp circuit is powered by a 9 volt PP3 battery and connected to the telephone __ Designed by D Mohankumar

Telephone Line In-Use Indicator -  This circuit gives a visual indication of whether a telephone line is in use or not, helping two or more people sharing the line to avoid interrupting each other's calls.  As...___ Electronics Projects for You

Telephone Off-Hook Indicator -  This circuit provides a steady logical "high" indication when the telephone is off its hook.  Operation is as follows:During the off-hook condition, DC telephone line voltage flows through clamping diodes CR1 and CR2, which develop about 1.5 volts across resistor R1.  This voltage is provided to the input of optical coupler U1 via current-limiting resistor R2, turning on U1's internal light-emitting diode.  Under these conditions, U1's NPN output transistor turns on, providing the +5 to +15 volt logic "high" level at its emitter, pin 4.  Pin 4 of the coupler may be connected to subsequent indicator circuitry, such as a transistor-controlled lamp or audible device.   __ Designed by Arthur Harrison

Telephone Status Indicator -  "Hello"  meet BUSYER-7Z.  The BUSYER-7Z is an educational telephone line busy indicator kit.  It lets you know if someone else is on the phone, line in-use (line is off-hook) before you picking up.  Large bright LED will indicate the phone line in-use status.  No more “Ops, ” “I’m sorry, ” “I didn’t mean to interrupt, ” “I’m on the phone.  ” The BUSYER-7Z will light when the phone line is off-Hook.  It will ends interruptions by indicating that you are “On the phone.  ” __ Contact: Kit from Elich Industrial Development, Corp

Telephone Status Indicator for 4 Lines -  Many home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Temperature Indicator -  This circuit sets off a buzzer after the last LED (led4) is lit.  It is a simple but fun circuit to experiment with.  You can replace the buzzer with something else, add a trimpot to adjust sensitivity, etc, etc.  The possibilities are endles __ Designed by Tony van Roon  VA3AVR

Temperature Indicator-Cum-Controller -  Here is an easy-to-construct temperature indicator-cum-controller that can be interfaced with a heater’s coil to maintain the ambient room temperature.  The controller is based on Atmega8535 microcontroller, which makes it dynamic...___ Electronics Projects for You

Three-Volt Low Battery Voltage Flasher -  Many battery powered devices use two AA alkaline cells.  Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating.  The hobby circuit below can be connected to a 3v battery, to give you some . . . Hobby Circuit designed by Dave Johnson P.E.-January, 1998

Tiptronic-Style' Gear Indicator -  It's easy to build and indicates the selected gear in both manual and automatic cars on a digital readout.___ SiliconChip

Transients Indicator -  Instant voltage transients are common in the power lines especially in places where machinery is operating.  Inductive loads and high power transformers creates transients and spikes in the mains lines.  Such voltage fluctuations are dangerous to SMPS based power supply and Microcontrollers.  Here is a simple circuit that __ Designed by D Mohankumar

Transmit to a Remote LED Indictor 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 . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2008

Tripler Converts 5 Volt to 15V -  App Note #297 By configuring a charge-pump voltage doubler as a tripler, you can readily derive 15V from 5V (Figure 1).  A 15V rail is useful for powering op amps, LCD-bias circuits, and other low-current applications.  The connections shown configure the IC1 voltage doubler as a tripler.  The no-load output___ Maxim Integrated

Two Line Telephone Line Status Indicator -  Many home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation.  The circuit is line polarity insensitive . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Two Transistor Oscillators -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro amp of current. . . Circuit by David Johnson P.E.-December, 2002

Two-Transistor Low Power Oscillators -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro amp of current . . . Hobby Circuit designed by Dave Johnson P.E.-December, 2002

Ultra Low Power Detects Clear Fluid -  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 . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2005

Ultra Low Power LCD Indicator -  This circuit serves as an ultra-low power replacement for multiple LED on-off indicators.  It also has the advantage of being easy to read in full daylight.  With the parts shown, it is possible to display four bits of information.   __ Designed by G. Forrest Cook

Version 4 of a DC Current Indicator -  The circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode . . . Hobby Circuit designed by David A. Johnson P.E.-October, 2005

Version a of 1.5v LED Flasher -  To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency.  A small 1.5 volt alkaline N cell should flash the LED for a full year.  It too uses a "charge pump" technique to provide a LED the needed voltage. . . Circuit by David Johnson P.E.-June, 2000

Visual AC Mains Voltage Indicator -  You should not be surprised if someone tells you that the mains voltage fluctuation could be anywhere from 160 volts to 270 volts.  Although majority of our electrical and electronics appliances...___ Electronics Projects for You

Voltage indicator -  The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-purpose analogue voltmeter.  The status of the mains voltage is available in the form of an LED bar graph___ Electronics Projects for You

Voltage indicator transitions between colours -  EDN-Design Ideas 03/02/2015    Using a two-colour LED, This Design Idea indicates power-on and voltage level.__ Circuit Design by Einar Abell

Water Flowing in Pipe Indicator -  The vibrations associated with water flowing through a pipe are picked up by an inexpensive piezoelectric wafer.    The signal from the wafer is first boosted by a micropower transistor amplifier and then fed to an ultra low power voltage comparator.     When the vibration signal has sufficient amplitude, a FET transistor switch is activated…[Circuit designed by Dave Johnson P.  E.  , 6/06/2009]. . . Circuit by David Johnson P.E.-July, 2009

Water Level Alarm -  A circuit that offers visual indication of fluid level in a vessel, with a switchable audible alarm.  Example uses would be to monitor the level of water in a bath or cold storage tank.   __ Designed by Andy Collison

Water Level Indicator with alarm -  This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full.    The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.  When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch __ Designed by Radioland.nt.au

Water-Level Indicator -  Many a time we forget to switch off the motor pushing water into the overhead tank (OHT) in our households.  As a result, water keeps overflowing until we notice the overflow...___ Electronics Projects for You

Water-Level Indicator using 7-Segment Display -  This water-level indicator uses a 7-segment display, instead of LEDs, to indicate the water level (low, half and full) in the tank.  Moreover, a buzzer is used to alert you of...___ Electronics Projects for You

Water-Tank Overflow Indicator -  Water is a vital but scarce natural resource.  To prevent water wastage, this water-tank overflow indicator comes in handy.  It gives audio as well visual alarm whenever the water tank overflows.Fig....___ Electronics Projects for You

Web-Based Water-Level Monitor & Pump Controller -  Several articles about water-level controllers for overhead tanks have been published in earlier issues of EFY magazine.  But the project we are going to share today is new and unique.  So...___ Electronics Projects for You

Wireless LED Flasher -  There are times when you would like to flash a LED through a thick plastic case without wires.  The circuit below performs this feat.  It can be powered from a supply ranging from 3v to 6v.  It draws about 300ua of average current at 5v. . . Circuit by David A. Johnson P.E.-January, 2011

Wireless 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 David Johnson P.E.-July, 2006


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

 


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