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Indicator Circuits
Indicators:  #'s - B      C - D      E -  F       G - H      I - L       M - O      P - Q      Rs      T - Z
Last Updated on: Tuesday, August 18, 2015 06:54 AM


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.,  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 1.5volt 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]

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

1 LED Indicates Two Power States -  12/05/96 EDN Design Idea    Uses a single bicolor LED to indicate both power-on and blown-fuse conditions. . .  [by Jim Hagerman, Hagerman Technology, San Diego, CA]

 

1 Line Telephone Line Status Indicator -  This circuit monitors one phone line . . . [Circuit by David Johnson P.E.,  06/10/00]

 

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 1.5volt AA alkaline battery cell. The circuit uses a charge pump technique to provide . . . [Circuit by David Johnson P.E.,  06/04/00]

 

12 Volt Battery Low Indicator LM741 -  Plans for a battery low indicator for a 12 Volt battery using an LM741 operational Amplifier. . . .  [REUK-Renewable Energy UK website]

 

12 Volt Lead Acid Battery Monitor -  This simple circuit makes it possible to monitorcharging process to a higher level. . . .  [Tony van Roon's circuit]

120 & 240VAC LED Voltage Indicator -  Useful for power lines control. Simple, transformerless circuitry. . .  [Flavio Dellepiane's web site]

 

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 battery level indicator for car batteries -  This kit measures battery voltage. The red LED (closest to the IC) indicates a low status - 11. 5Volts or less. The yellow LED indicates 50% charge - 12. 0V. The green LED indicates 12. 6V or full charge. This kit also measures the charging status. Turn the charging system on - or start the vehicle. The red LED (at the extreme end from IC) indicates overcharge - 15. 5V. The green LED indicates maximum charge voltage - 14. 5V. The yellow LED indicates normal charging voltage - 13.2V. . . .  [CdS Electronic's website]

 

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 Cell Lithium Ion Battery Charger -  This circuit was build to charge a couple series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. The charger operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage. . .  [Designed by Bill Bowden]

 

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 Level Audio Power Indicator -  Battery-operated3 LED display that connect it to loudspeaker output. . .  [Flavio Dellepiane's web site]

 

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 & 8 Infrared-Proximity Detectors (TSOP4830) -  In this circuit the TSOP4830 is used as a sensitive infrared detector that does not require shielding from room lighting. The detector will work under almost any lighting condition from complete darkness to full sunlight. scroll down for this one. . . .  [from Rob Paisley's Model Train web site]

 

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]

 

50 MHz Frequency Counter Voltage Meter & SwR/PWR Indicator -  This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876. . .  [by Aleksander Stare]

 

7-segment Display Water-Level Indicator -  It is a circuit that indicates the level of water in a tank (low, half or full) on a 7-segment display. It uses a buzzer to alert the user about water overflowing from the tank. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved.]

 

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Indicator Circuits
Indicators:  #'s - B      C - D      E -  F       G - H      I - L       M - O      P - Q      Rs      T - Z


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