Ringing Phone Light Flasher

I have received several emails asking how to connect up some lights so that when the phone rings, they flash. This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop. Here is such a device.


Partlists:

• C1 1 0.47uF 250V Capacitor
• R1, R2 2 10K 1/4 W Resistor
• R3 1 1K 1/4W Resistor
• D1, D2 2 20V 1/4W Zener Diode
• D3 1 1N4148 Diode
• Q1 1 2N3904 NPN Transistor 2N2222
• U1 1 4N27 Opto Isolator
• RELAY 1 Solid State Or Regular Relay (See Notes)
• MISC 1 Case, Wire, Board

Notes:

1. You may need to use a lower voltage zener for D1 and D2.
2. You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly.
3. Be very sure that you have not accidentally connected 120V to the phone line when building and installing this circuit.

Phone Busy Indicator

Have you ever been using the modem or fax and someone else picks up the phone, breaking the connection? Well, this simple circuit should put an end to that. It signals that the phone is in use by lighting a red LED. When the phone is not in use, a green LED is lit. It needs no external power and can be connected anywhere on the phone line, even mounted inside the phone.

Partlists

• 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

Notes:

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.

Cut Phone Line Detector

A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn't take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system.

• R1, R2, R3 3 22 Meg 1/4 W Resistor
• R4 1 2.2 Meg 1/4 W Resistor
• C1 1 0.47uF 250V Mylar Capicitor
• Q1 1 2N3904 Transistor or 2N2222
• Q2 1 2N3906 Transistor
• Q3 1 IRF510 Power MOSFET
• D1 1 1N914 Diode
• Load 1 See "Notes"
• MISC 1 Wire, Phone Connectors, Circiut Board

Notes:

1. The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut.
2. If the circuit is connected to a security system or other circuit, both circuits must be electrically isolated from each other using an opto-isolator, relay, etc. This also means that the Cut Phone Line Detector must be powered by a seperate 9V supply.