TM 11-5805-689-14
and to a logic 1 for four seconds. The collector is DC
automatic switching center receives the 570 Hz seize
coupled through resistor R115 and diode CR113 to
acknowledge signal from the Converter, the 2250 Hz
the base of the 425 Hz oscillator controlled transistor
signal being transmitted from the automatic
Q107. Therefore, the 425 Hz oscillator is on for two
switching center causes the transistors in the turn on
seconds and is off for four seconds. The output of the
delay circuit to return to their normal state. The
action of the turn off delay circuit is as follows:
4 2 5 Hz oscillator is taken from the emitter of
When transistor Q14 return to normal (switches off),
transistor Q108 and coupled to the base of tone gate
base drive is provided to transistor Q16, in the turn
transistor Q24. The 425 Hz ring-back signal is now
off delay circuit through resistors R39, R40, and
inductively coupled from the primary of the output
diode CR22. Transistor Q16 switches on causing its
collector to go to a logic 0. The logic 0 is coupled to
automatic switching center switchboard as ring-back
capacitor C9, Initially all the current flow is from the
t o n e . When the operator services the call, the
positive voltage source through resistors R39 and
ACCESS pushbutton is depressed to clear the latch
R43, through capacitor C9, diode CR23 and tran-
w h i c h inhibits the ring-back tone. Momentary
sistor Q16, to negative battery. This holds transistor
depression of the ACCESS pushbutton applies a
Q17 off and no change is seen at the collector of the
ground through diode CR50 which clears the latch
detector output transistor Q28. Capacitor C9 now
and inhibits the ring-back tone. The operation of the
charges through resistors R43 and R39 and base
3 to 10 second release timer will be described later
drive is provided for transistor Q17 after a delay
along with the presentation of a functional block
w h i c h is established by the time constant of
capacitor C9, resistors R43 and R39. When tran-
pushbutton S1 and momentary depression of the
sistor Q17 starts conducting, transistor Q28 turns
RELEASE pushbutton (S2 on common module) by
off, thus a turn off delay of a nominal 450
milliseconds is provided per specification. The action
activates the release timer. The action of the release
of transistor Q28 switching off removes the enable
timer is as follows: Depression of the RELEASE
from the 570 Hz tone gate and 570 Hz O S C. This
pushbutton changes the potential on resistor R52 to
i n h i b i t s the sending of 570 Hz signal to the
a positive voltage. As long as the RELEASE push-
automatic switching center switchboard. The 425 Hz
button is held depressed, nothing happens in the
tone gate circuit is now enabled. This is because the
timer circuit. When the operator releases the push-
latch transistor Q30 is still conducting and the logic
button, the potential on resistor R54 changes to
0 has been removed from diode CR46 in the base
n e g a t i v e battery. Current now flows from +V
circuit of the 425 Hz tone gate control circuit Q29.
through resistor R56, capacitor C13, and resistor
The 425 Hz signal generated by the Converter is the
R54 to negative battery. The potential at the base of
ring-back signal. This ring-back signal is on for two
transistor Q20 switches from approximately 0.7 volt
seconds and off for four seconds, and is controlled by
positive to 4 volts negative. Transistor Q20 which is
the interrupter circuit to be explained next. The
normally conducting, now switches off causing its
collector to go to approximately 2 volts positive.
which is on for two seconds and off for four seconds.
T h i s provides base current to transistor Q21
Transistor Q21 switches on and provides base drive
This circuit consists of two transistors Q105 and
to transistor Q22. The collector of transistor Q22
Q106, resistors R111, R112, R113, R114 and R115,
then switches to a logic 0. This condition is main-
d i o d e s CR111, CR112, CR113 and CR114, and
capacitors C108 and C109. This circuit is controlled
t a i n e d until capacitor C13 charges up through
by each individual channel through diodes CR120,
resistor R56 to a voltage sufficient to cause tran-
sistor Q20 to conduct (0.7 volts positive). The logic 0
CR121, and CR122, from PNP latch transistor Q31.
When power is applied, transistor Q106 conducts
at the collector of transistor Q22 is coupled through
and the collector goes to a logic 0. This logic 0 is
diode CR16 to capacitor C6. This tunes the 2250 Hz
coupled to the base of transistor Q105 through
detector to 570 Hz to enable receipt of the 570 Hz
capacitor C109 holding transistor Q105 off.
acknowledge signal. The logic 0 is also coupled to the
capacitor C109 charges up through resistor R113.
570 Hz gate transistor base through diode CR17,
When the capacitor charges up to the proper positive
providing base drive for transistor Q9. The resultant
voltage, transistor Q105 turns on. The collector of
positive potential at the collector of transistor Q9
transistor Q105 goes to a logic 0 and is then coupled
provides the proper bias condition for the 570 Hz
through capacitor C108 to the base of transistor
driver transistor Q8. The logic 0 at the collector of
Q106. This turns transistor Q106 off until capacitor
transistor Q22 is also coupled through CR103 to the
C108 charges up through resistor R111. The collector
2600 Hz tone gate Q23 to enable this circuit. The
of transistor Q106 goes to a logic 0 for two seconds
2600 Hz oscillator transistor Q102 is connected
3-6