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4. CIRCUIT DIAGRAM IN THE TELE-
PHONE
In this section, let's learn about the basic circuits inside a telephone.
4.1
Dial Telephones
The Fig. 1-13 shows the basic circuit of a dial telephone.
However, in actual fact, hook switch HS2 is provided in addition to switch
HS1 on dial telephones as shown in the Fig. 1-14. The bell circuit is closed
and short-circuited by the switch HS2 when the handset is picked up.
Ringing of the bell by dial pulses is thus prevented.
Dial telephones are also provided with a dial shunt contact DS to prevent
noise caused by the entry of dial pulses on the receiver. The DS closes
when you start dialing and opens when the dial has finished returning to its
start position.
DP
R
T
HS
Fig. 1-13 Basic Circuit of Dial Telephone
DP
HS
2
Bell
DS
HS
1
Fig. 1-14 Circuit of Dial Telephone
BASIC OF TELEPHONE
T: Transmitter
R: Receiver
DP: Dial pulse contact
HS: Hook switch
T: Transmitter
R: Receiver
DP: Dial pulse contact
R
DS: Dial shunt contact
HS
: Hook switch 1
1
T
HS
: Hook switch 2
2
1
2
3
4
5
6
ït
çi
1–13
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