What Are Keypad Phones?

Key telephones are a type of telephones that use the keypad as an interface component when the telephone is sending numbers, provide input signals to the numbering integrated circuit, and emit pulse or dual-tone signals. A push-button telephone is a type of automatic telephone. Compared with a traditional dial-type automatic telephone, it has the same parts and different parts.

Key telephones are mainly composed of hook springs,

1. Replace the mechanical dial with the key dial

The mechanical dial is a mechanism for the user to send a pulse number selection signal. Using a series of actions of mechanical parts, the on-off of the two sets of reed contacts is finally achieved. One set of pulse reed contacts is used to interrupt the user circuit and send out uniform DC pulses. The number of pulses is the same as the number sent to control the action of the automatic telephone exchange. Another set of short-circuit reed contacts has three functions: one is to prevent the pulse current from entering the receiver of the calling user, which produces a harsh "click" sound; the other is to prevent the pulse current from entering the user's microphone to avoid the speaker carbon The particles are sintered due to current shock; the third is to reduce unnecessary additional impedance of the pulse circuit. The key dial is also called an electronic dial, which is composed of a key switch and an electronic circuit. It has two types: one is a DC pulse-type key dial; the other is a dual-tone multi-frequency key dial. For pulsed key dials, it is the combination of key movements and electronic circuits that emit the same DC pulses as mechanical dials to achieve the same circuit action as mechanical dials. For dual-tone multi-frequency key dials, A new audio number selection method replaces the old mechanical dial pulse number selection method, which also achieves the purpose of controlling the automatic switch operation. ^[2]

Dual-tone multi-frequency number-selection button telephone

A dual-tone multi-frequency push-button telephone is a telephone that uses an audio keypad instead of a rotary dial. This phone replaces the dial pulse signal with a dual tone multi-frequency signal. Its signal is composed of high and low audio signals. Among them, 4 audio signals above 1000Hz (referred to as "high frequency group"), 4 audio signals below 1000Hz (referred to as "low frequency group"), a combination of two out of eight, representing the number of o-9 and other function codes . There are 16 combinations of this 4 × 4 coding method, but generally a button phone only uses 12 combinations of three high-frequency signals and four low-frequency signals, as shown in Figure 3-2. Each time a user presses a number button, it sends out a combination of two audio signals (representing a number) at the same time. The time required to send each number is basically the time that the button is pressed. Unlike a dial pad, each pulse needs to be sent. About 100 milliseconds. There is also an interval of about 800 milliseconds between the digits, so the key number issue greatly reduces the time required for dialing. Another advantage is that the number can be re-issued after the voice channel is connected (digital signals and various functional signals are issued), thereby expanding the use of functions. This type of push-button telephone sends a dual-tone multi-frequency signal to the telephone office (referred to as

First, its numbering parameters are completely guaranteed by the electronic device, which is very stable and easy to operate; second, the voice distortion is small during a call; third, the ringing tone is a two-tone mode, the sound is pleasant, and the ringing can be easily added Volume and tone adjustment.

In addition, it adds many additional features, such as:

Number resend

After dialing the number and confirming the busy tone from the exchange, you can hang up temporarily and wait for a few seconds before going off-hook. Just press the Redial key ("Redial" key) to re-issue the phone number you just entered.

Number storage and speed dial

That is, some commonly used telephone numbers are stored in the telephone in advance, and when needed, press 1 or 2 address keys to complete the number sending function. The specific methods for storing and abbreviating dialing of various telephone numbers are different, and can basically be divided into one-button abbreviated dialing and two-button (or three-button) abbreviated dialing. One-touch speed dialing is equivalent to one key representing a telephone number. If there are many stored numbers, more keys are needed, and they are regularly arranged and labeled to become a telephone number dial. One-touch abbreviated dialing can also be conveniently used as a phone number sticky note: Fixed a key as a sticky note, when a phone number is asked during a call, it will be stored in the key address, and then go off-hook and press this Send a number with a single key.

Three-way call using "R" key

The "R" key is a function key used by the telephone in conjunction with a program-controlled exchange. For example, when two users talk, a third party is required to talk together (three-party conversation). At this time, the party that has already talked is required to press the "R" key to hear the dial tone and then dial the number to call the third party. Under what circumstances the "R" key is used, it is subject to the regulations of the local telecommunications bureau.

Lock number

The lock function is that the phone can limit the first (or first few) digits of the phone number sent. If the forbidden number key is pressed first, the phone does not make a dial tone, making the call unsuccessful. We stipulate that the first digit when dialing long distance is "o", so the lock function of the telephone in our country is basically to lock the number whose first digit is "o".

Receiving

When the line is long, sometimes the phone volume is too low to be heard clearly. At this time, you can use the receiver's booster function, and hit to increase the receiver volume appropriately. Because the key telephone receiver circuit uses an amplifier, it is very simple to achieve this function, as long as a switch is used to control the amplifier to increase the amount of amplifier appropriately. Because this kind of amplification does not change the signal-to-noise ratio, the effect is not obvious when the noise in the line is large.

Send closed tone

When a telephone with the function of sending a closed tone key is pressed, the voice will not be sent to the line through the microphone, so the other party cannot hear it. This applies to situations where you talk to others around you for a short time while you are on the phone, but you don't want the other person to hear. Some phone descriptions call this feature a security feature, sometimes using the "*" key.

other

Touch-tone telephones generally also have functions such as inserting waiting time (pause function) during dialing, pulse / tone compatible dialing, P / T conversion on-hook hold, and so on. The meanings of some common function keys of the key telephone are as follows:

STORE memory key for storing frequently used phone numbers.

TIMERTimer key, can time and report the call time.

PAUSE ... A pause button for a dedicated automatic telephone exchange.

FLASH flash keys one by one, which can flash to catch two emergency calls.

AUT0Auto dial key, used to retrieve any stored number.

MuTEMute key, also known as silent key. Press this key to prevent the other party from hearing your voice.

REDIALRedial button, you can redial the last dialed phone number.

AMPAmplifier switch. Dial ON to access the voice amplifier. Set it to OFF when not in use. ^[2]