Casio KP-C10 - PC Tag Writer Especificaciones descargar pdf (Pagina 100)

CIRCUIT IDEAS

supply, diode D4 is reverse biased and

acts as an ‘off’ switch, inhibiting

the conduction of diode D3, which al-

lows normal functioning of transistor

T2. The inverter can be switched ‘off’,

when not required, by using ‘on/off’

switch S1.

Low battery voltage indicator cir-

cuit comprises transistor T3, senser di-

ode D6, LED 2, variable resistor VR1,

and resistors R4 through R6. The

low battery indication can be adjusted

from 4.7V to 5V by using variable re-

sistor VR1. When the battery voltage

is above 4.7V, zener diode D6 comes

out of conduction, keeping transistor

T3 at cut-off level. At the same time,

LED2 gives the indication of low bat-

tery volt-age.

The whole circuit can be assembled

in a cabinet of emergency light suitably.

vides DC path for charging of the bat-

tery. But, in the absence of AC mains

PARALLEL TELEPHONES

WITH SECRECY

S.C. DWIVEDI

MANUJ PAUL

O

ften a need arises for connec-

tion of two telephone instru-

ments in parallel to one line.

But it creates quite a few problems in

their proper performance, such as over

loading and overhearing of the conver-

sation by an undesired person. In order

to eliminate all such problems and get

a clear reception, a simple scheme is

presented here (Fig. 1).

This system will enable the incom-

ing ring to be heard at both the ends.

The DPDT switch, installed with each

to the line.

To receive a call at an end where

the instrument is not connected to

the line, you just have to flip the

toggle switch at your end to re-

ceive the call, and act as usual to

have a conversation. As soon as the

position of the toggle switch is

changed, the line gets transferred

to the other telephone instrument.

Mount one DPDT toggle switch,

one telephone ringer, and one tele-

phone terminal box on two wooden

electrical switchboards, as shown in

Fig. 3. Interconnect the boards us-

ing a 4-pair telephone cable as per

Fig. 1. The

system is

ready to

use. Ensure

that the two

lower leads

of switch S2

are con-

nected to

switch S1

after rever-

sal, as

shown in

the figure.

Lab.

Note: The external ringer for the project

as shown in Fig. 2., was designed/fab-

ricated at EFY Lab.

of the par-

allel tele-

phones,

connects

you to the

line in one

position of

the switch

and discon-

nects you in

the other

position of

the switch.

At any one

time, only

one tele-

phone is

connected

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