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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.
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- 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.
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- 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.
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- 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...
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- 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.
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- AC Current Indicator Light
This circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being
drawn by a load. It is especially useful for remote lights, where you may not be able to see if the lamps are receiving power.
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- ACCEPTABLE VOLTAGE INDICTOR
I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed. The circuit can also be used to adjust a particular voltage be within
specific high or low limits. The three LEDs will indicate if the voltage is high, low or OK. When connected to other converters, such as a frequency to voltage converter,
a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level.
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- Electrical Current Indicator
I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts. The circuit turns on a small LED, whenever it detects current flowing to
a remote load.
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High DC Current Indicator NEW
A while back, someone requested a simple method to indicate when 20 to 50 amps of DC current was flowing through a wire. The circuit below works well and is about as simple as you
can get. A sensitive reed relay from www.Jameco.com acts as the current sensor. The
magnetic field produced by such a current is enough to close the relay contacts, if one or two turns are wound around the relay. The turns do not have to be tight. I was able to
close the contacts with two turns about 2 inches in diameter with 20 amps. A simple LED and resistor can be used to indicate the current by tapping into the automotive +12v supply.
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- Moving Air Indicator
Many months ago a Discover Circuits reader wanted a method to indicate when a fan was blowing air. He didn’t want to route any electrical wires to a sensor near the fan.
Instead he wanted all the electronics for both the fan and other circuits mounted some distance away from the fan. I scratched my head a bit....
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- RS232 Serial Interface Status Indicator
I designed this circuit many years ago and have used it several times since. It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data
communications link. The thresholds are set at plus 3 volts and minus 3 volts. Two dual color LEDs are used as indicator lights.
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