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Phone Busy Indicator Diagram

Phone Busy Indicator DiagramPhone Busy Indicator Diagram

Have you anytime been application the modem or fax and addition abroad picks up the phone, breaking the connection? Well, this simple ambit should put an end to that. It signals that the buzz is in use by lighting a red LED. When the buzz is not in use, a blooming LED is lit. It needs no alien ability and can be affiliated anywhere on the buzz line, alike army central the phone.


1. This is a very simple circuit and is easily made on a perf board and mounted inside the phone.

2. LED1 and LED2 flash on and off while the phone is ringing.

3. Do not worry about mixing up the Tip and Ring connections.

4. The ring voltage on a phone line is anywhere from 90 to 130 volts. Make sure no one calls while you are making the line connections or you'll know it. :-)

5. In some countries or states you will have to ask the phone company before you connect this to the line. It might even require an inspection.

6. If the circuit causes distortion on the phone line, connect a 680 ohm resistor in between one of the incoming line wires and the bridge rectifier.

Phone Busy Indicator Diagram Part List

R1 1 3.3K 1/4 W Resistor
R2 1 33K 1/4 W Resistor
R3 1 56K 1/4 W Resistor
R4 1 22K 1/4 W Resistor
R5 1 4.7K 1/4 W Resistor
Q1, Q2 2 2N3392 NPN Transistor
BR1 1 1.5 Amp 250 PIV Bridge Rectifier
LED1 1 Red LED
LED2 1 Green LED
MISC 1 Wire, Case, Phone Cord