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Circuits designed by David Johnson, P.E. Last Updated on:
Thursday, December 01, 2011 07:16 AM The contents &
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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.
120vac/240vac
Indicator Two LEDs indicate if a power line has 120vac or 240vac voltage on it.
125kHz Wireless Smart Key Detector
This circuit will turn on an indicator light whenever it detects a smart car key
containing an RFID chip.
12v Lamp Current Indicator This circuit
turns on a LED indictor light whenever DC current flows into a 12v lamp.
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.
