hen_45 asked in Science & MathematicsEngineering · 9 months ago

# I have an old phone made in the 1980s and would like to know what the wires do.?

There are two wires, a green and a red. I would like to use this in a project but cannot find infomation on what these two wires do and how much voltage/amps they take. Can anyone here help me out?

Relevance
• Anonymous
8 months ago

Are you wanting to use the phone?

Or

Are you wanting to use the wires?

If you connect the 2 wires to your present phone line, it will operate.

If it's a Touch-Tone phone, and it won't dial or make tones, then reverse the connections.

Simple.

p.s.

If you use a 1.5 volt battery you can talk into the mouthpiece and hear your voice in the earpiece.

If it's a Touch-Tone phone, if you connect at least 5 volts DC you can hear yourself talk and dialing tones.  If it won't make tones, then reverse the connections.

Fun!

• Steven
Lv 7
9 months ago

A "POTS" phone uses 3 different interfaces.

1. When on-hook, the phone is a capacitor coupled ringing circuit that blocks DC but accepts a ~20Hz high voltage ~90VAC to ring the bell, ~5KOhm.

2. When off-hook, the phone draws about 30mA DC to activate the phone exchange. This drops the -48VDC open voltage to about -7 VDC. Pulse dialing interrupted this current one pulse per number, and 10 times for zero. "Touch-tone" dialing uses two tones of 8, selected by the keypad matrix. Negative DC voltage is used to reduce  corrosion.

3. During the call, a "hybrid" circuit partially separates local and remote audio signals on a 600 Ohm  audio transmission lines, although the impedance is actually frequency dependent because long phone lines are actually about 100 Ohm.

Rural phone lines typically use 3 wires, ie 2 wires + ground. The ground is used for the ringing circuit only.

The choice of these voltages etc are historical, dating back long before your 1980 phone to a time when the entire system was electro-mechanical and no electronics were available.

• 9 months ago

The red and green wires carried the signal on the system. They are very small wires and do not carry Voltage and Amperes (well, they do but at very small amounts). A phone has a microphone and a speaker connected in series between the red and green wires. When you talk into a microphone, it converts the sound waves into small electrical signals on the red and green pair of wires. The speaker will convert those electrical signals into sound waves. The telephone does not generate power, it generates an electrical signal on the telephone line.

• 9 months ago

In the US, POTS phones (Plain Old Telephone Service) were driven by a 20 mA loop.  The phones had an impedance of 600 ohms, so the voltage across tip and ring with the handset offhook was about 12 volts.  (anything between 6 and 24 volts will work OK)

If you have two phones and want them to talk to each other...  Connect the green wire or one to the red wire of the other, then connect the remaining green and red wires to a 12 - 24 volt source.

• 9 months ago

They are the tip and ring wires of the phone and operate @~32V.

• 9 months ago

HOOK IT TO THE INDOOR PHONE SOCKET VIA A PHONE JACK. THESE TWO WIRES OBTAIN BOTH SIGNAL AND 50Vdc POWER FROM PHONE COMPANY THAT ARE CARRIES FROM THE PHONE LINE.

• roger
Lv 7
9 months ago
• Andy
Lv 6
9 months ago

The two conductor were commonly known as "tip" and "ring". See below for information on this and how telephone circuits work.

https://en.wikipedia.org/wiki/Tip_and_ring

http://telecom.hellodirect.com/docs/Tutorials/TelW...

https://en.wikipedia.org/wiki/Plain_old_telephone_...

• 9 months ago

If you cut the red wire, the phone will explode.

Source(s): Terminator 2
• Anonymous
9 months ago

positive and ground