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Indicator Circuits, Page 1

Circuits designed by David Johnson, P.E.

Last Updated on: Thursday, April 07, 2016 02:04 PM

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Dave's Indicator Circuits:  Page 1,    Page 2,    Page 3,   Page 4

1 Line Telephone Line Status Indicator  -  This circuit monitors one phone line . . . [Circuit by David 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 Johnson P.E.,  06/04/00]


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]


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.,  07/10/06]

 

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.,  07/09/06]

 

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.,  02/10/02]


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.,  07/01/00]


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.,  03/11/99]


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.,  06/10/00]


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.,  12/14/02]


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.,  01/01/98]


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.,  04/11/10]


4 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 . . . [Circuit by David A. Johnson P.E.,  06/10/00]

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