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Indicator Circuits   Page 1
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Last Updated on:
Thursday, October 30, 2014 09:22 AM
 

Circuits designed by Dave Johnson, P.E. :
 

  • 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 the LED the needed voltage.
  • 1.5V LED FLASHER VERSION B
    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.
  • 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.
  • 3v 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 warning when the battery is nearing its end of life.  It will flash a LED when the battery voltage drops to about 2.4 volts.  The electronic circuit draws only 1ua of current in standby mode and jumps to only 20ua when flashing, so it can safely...
  • 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.

  • Alkaline Low Battery Voltage Indicator
    In many battery powered systems a user would like to know when it was time to replace the batteries before they were completely discharged, causing the device being powered to fail completely.  Alkaline batteries have an open cell voltage of about 1.5 volts.  As they are discharged, the voltage slowly drops.  When the cell voltage reaches about 1.25v, they have delivered about 90% of their stored energy.  The circuit below monitors the voltage of two alkaline cells in series and begins flashing an efficient red LED when the total battery voltage drops below 2.5v, alerting the user that the batteries need to be replaced.  The circuit takes advantage of some new voltage comparators from Touchstone Semiconductor.  The TSM9118 has an internal 1.25v reference and an open drain output while drawing an astoundingly low 0.7ua...[Circuit of the Week designed by David Johnson, P.E.]
  • 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.


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
1 Line Telephone Line Status Indicator -  This circuit is similar to the above circuit, but only monitors one phone line..... [Designed by David A. Johnson]
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….(design added 11/08)
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 the LED the needed voltage. …. [Hobby Corner Circuit by Dave Johnson]
1.5v LED Flasher Version B -  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..... [Designed by David A. Johnson]
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 monitor  charging process to a higher level…. [Tony van Roon's circuit]
120 & 240Vac LED Voltage Indicator -  Useful for power lines control.  Simple, transformerless circuitry  (added 2/07)
120 VAC / 240 VAC indicator -  Two LEDs indicate if a power line has 120vac or 240vac voltage on it.  (added 7/06) …. [Designed by David A. Johnson]
125kHz Wireless Smart Key Detector -  This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip.  (added 7/06) …. [Designed by David A. Johnson]
12v Lamp Current Indicator -  This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp.  (added 7/06) …. [Designed by David A. Johnson]
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..... [Designed by David A. Johnson]
3 Level Audio Power Indicator -  Battery-operated3 LED display that connect it to loudspeaker output (added 04/02)
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.  It use an inexpensive IC from Panasonic that is connected to an efficient LED flashing circuit.  When the battery voltage drops below a certain point the circuit flashes the LED.  In the off state the circuit draws only 1uA, while in the active flashing state it draws 20uA.   Published in EDN, Jan 2, 1997 …. [Designed by David A. Johnson]
3v 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 warning when the battery is nearing its end of life.  It will flash a LED when the battery voltage drops to about 2.4 volts..... [Hobby Corner Circuit by Dave Johnson]
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..... [Designed by David A. Johnson]
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.....(electronic diagram added 6/03)

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