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Phase-sequence indicator uses feW passive components - 07/06/06 EDN Design Idea Debug three-phase power-line wiring with this easily constructed
circuit. . . [by Metodi Iliev, University of California—Berkeley]
Phone Busy Indicator - Simple busy indicator, does not meet regulations of many countries because this circuit
draws excessive continuous current from the ph1-line even when not active and this can cause problems with
Telephone system. . . . [Design by Aaron Cake]
Phone in Use - The circuit I
built gives a visual indication at each extension when any extension is off-hook. It is line-powered, and the
maximum number that can be used on our system is three. Since they all draw power at the same time to light the
LEDs, any more indicators would cause an off-hook condition. . . [Designer is Kevin Carver]
Phone in use indicator - This
circuit is useful to show when your line is busy. I used for this a pair of smt transistor, the LEDs on when the
voltage drop down to 40 v. . . . [designer identified as Alfred73]
Phone In Use Indicator - With this circuit mounted in or near every phone in the house, it will allow users to know
if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the
tip and ring terminals drops to 10 volts or less. . . . [Randy Linscott]
Phone in use
indicator 1 - Use a CMOS 4049 Hex Interter because
(supposedly) has high drive output. And since it's CMOS, it can operate with VCC from +3 to +15V. And it has a
high input impedence. . . . [Roger Petersen]
Phone in use
indicator 2 - LED will start blinking if a phone is in
use. . .
Phone in use
indicator 3 - Now here's some logic that should work fine
with the right zener and the right resistors and a couple of cheap NPN's 2n2222A's or 2n3904's (06's?). If you
get close to 25 volts with the new smart test boxes, a 20 volt Z may work fine. Choose R1 to limit current
through Z and have enough left to turn on NPN1 just enough to deprive NPN2, choose R2 for that, and you will need
to add a resistor R3 to protect the LED from overcurrent as needed, depending on the phone system you have!
. . . [Richard Steven Walz]
Phone in use
indicator 4 - The circuit I built gives a visual
indication at each extension when any extension is off-hook. It is line-powered, and the maximum number that can
be used on our system is three. Since they all draw power at the same time to light the LEDs, any more indicators
would cause an off-hook condition. Some changes could be made to reduce the current draw, to allow using more
indicators, but the brightness of each LED would suffer. The LEDs I used are tiny, but. . . . [Kenneth Carver]
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