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Dave's Indicator Circuits: Page 1, Page 2, Page 3 |
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- High DC Current Indicator
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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- Remote LED Indicator Light -- NEW
There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the
internal infrared LED inside an opto-isolator has a lower voltage drop than the visible LED being tapped into. Using a darlington type opto-isolator also means very little current needs to be diverted to the isolator.....
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