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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.
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....
Automotive 12v Electrical System Voltage Indicator - This battery powered
unit is designed to quickly aid troubleshooting of 12v electrical systems in a car.
Three LEDs proved a visual indication of a +12v, ground or an open circuit voltage
level. …. [Hobby Corner Circuit by Dave Johnson]
Bad Light Bulb Indicator - This request came from a Discover Circuits
visitor. He wanted to turn on a LED indicator light whenever a circuit
detected a burned out tail/brake light on a car or truck. The circuit shown
below uses a transistor switch, to detect current flowing through a low value
resistor. If current is flowing to a light bulb, the circuit shunts current
around a LED light, keeping the LED turned off. If there is no current detected, the
LED turns on. The circuit should operate from 6v to 24v.... [Designed by David
A. Johnson]
Battery Charge Current Indicator
This circuit turns on a LED whenever it detects at least 25ma of battery charge
current. (added 7/06)
DC Current Indicator #4 - The circuit below uses some common components to
turn on an LED whenever DC current above a certain level is detected. The
circuit uses a very popular LM393 dual voltage comparator from National
Semiconductor and a common 1N4148 signal diode. The diode acts as a crude 0.7v
voltage reference. Only one of the comparators inside the 8 pin package is
used. A pair of resistors across the diode forms a voltage divider, which
produce a reference voltage of about 0.015v.... [Designed by David A. Johnson]
DC Current Indicator 6 - The circuit below is a simple way to indicate
when DC current is flowing through a wire. The circuit is designed so it will
turn on a LED indicator light, whenever the voltage drop across a shunt resistor
exceeds about 0.1 volts. The value of the resistor can be selected based on
the desired current flow. Although I show a circuit for 12v operation, the circuit
can be used over a wide range from 3v to perhaps 24v.... [Designed by David A.
Johnson]
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.
