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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 10, 2017 06:45 AM


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

Circuits Designed by Dave Johnson, P.E. :

1 Line Telephone Line Status Indicator This circuit monitors one phone line. . . Circuit by David Johnson P.E.-June, 2000

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 Johnson P.E.-June, 2000

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.-July, 2006

125khz Wireless Smart Key Detector  This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip. . . Circuit by Dave Johnson P.E.-July, 2006

12v Lamp Current Indicator This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp. . . Circuit by David Johnson P.E.-July, 2006

12v Touch Switch Exciter Circuit  This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.    It can support a cable length of about 2500 feet.    A typical remote switch circuit is also shown as well as a receiver circuit for those switches.. . . Circuit by David Johnson P.E.-February, 2002

175Khz Inductive Pulse Receiver  This circuit is discussed in more detail in the Experimenters Journal.  The receiverís six inch diameter coil detects the ring signal from the above transmitter and use a single NPN transistor to provided enough amplification for the signal to be easily viewed on an oscilloscope. . . Circuit by Dave Johnson P.E.-July, 2000

1uS Light Pulse Receiver + Post Amp  This circuit is designed to detect very weak light pulses lasting 1uS.  It uses a tuned LC feedback network to provide high sensitivity while giving high ambient light immunity.  A post voltage amplifier is included with a gain of about X20.  The circuit is described in more detail in the receiver section of my Handbook of Optical Through the Air Communications.    Note: The LF357 op amp is no longer available, this circuit is for reference only.. . . Circuit by Dave Johnson P.E.-March, 1999

2 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. . . Circuit by David A. Johnson P.E.-June, 2000

2 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 Dave Johnson P.E.-December, 2002

3 Volt Low Battery Voltage Flasher  This circuit is designed to monitor two alkaline cells   (3v) that form the battery often used in portable electronic equipment. . . Circuit by David A. Johnson P.E.-January, 1998

36-Hour Watchdog Timer  A watchdog timer is often used in computer systems to detect when a computer is hung up and is no longer running properly.  If it does become locked up and is not able to supply a reset pulse to the circuit within a defined time frame the timer times out a. . . Circuit by David A. Johnson P.E.-April, 2010

4 Line Telephone Line Status Indicato  rMany 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. . . Circuit by David A. Johnson P.E.-June, 2000


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

1 Line Telephone Line Status Indicator -  This circuit monitors one phone line. . . Circuit by David Johnson P.E.-June, 2000

1.2-12V/ 1A Low Voltage LED Indicator Power Supply with LM317 -  This is a 1.2, 12 V, max 1A power supply with a low voltage indicator LED.  The indicator part includes three diodes and one LED.  For example you are charging a battery, you can observe the charge status at that moment.  Another advantage of this circuit, when the drawn current exceeds 1A    (practically 0.85A) , the current protector in LM317.  

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 Johnson P.E.-June, 2000

1 Line Telephone Line Status Indicator -  This circuit monitors one phone line. . . Circuit by David Johnson P.E.-June, 2000

1.2-12V/ 1A Low Voltage LED Indicator Power Supply with LM317 -  This is a 1.2, 12 V, max 1A power supply with a low voltage indicator LED.  The indicator part includes three diodes and one LED.  For example you are charging a battery, you can observe the charge status at that moment.  Another advantage of this circuit, when the drawn current exceeds 1A    (practically 0.85A) , the current protector in LM317.  

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 Johnson P.E.-June, 2000

12 Volt Battery Low Indicator LM741 -  Plans for a battery low indicator for a 12 Volt battery using an LM741 operational amplifier.   __ Designed by REUK-Renewable Energy UK website

12 Volt Lead Acid Battery Monitor -  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

120 & 240VAC LED Voltage Indicator -  Useful for power lines control.  Simple, transformerless circuitry __ Contact: Flavio Dellepiane, fladello @ tin.it

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.-July, 2006

125khz Wireless Smart Key Detector -  This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip. . . Circuit by Dave Johnson P.E.-July, 2006

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

 


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