Muratec F-110 Field Engineering Manual page 59

Circuit Description
RINGER DIAL CIRCUIT
1) Ringer Circuit
• The ring detect circuit detects the ring signal by sending the bell signal sent from PSTN to the primary photo coupler
(PC814). At this point, C(1uF/250V) is used to match the ring impedance and R is coupled directly in order to prevent any
damage to the photo coupler due to ring voltage.
2) Dialing Circuit
• Dialing circuit is initiated only when the power is on and it is transmitted to line through the modem of main part (T2 trans)
3) External Hook Detect Circuit
• In the discrete LIU method, the external hook detect circuit is designed to use both the photo coupler and current detec-
tor in order to be used in all countries including the countries with low series resistance (Germany, Switzerland, Belgium,
Austria, etc.). To use photo coupler (PC814), you must carefully select the resister connected parallel (75 ) to the photo
coupler in order to satisfy the voltage drop standards of England and a few other countries. The diode connected to the
current detector pin (5/6) was used to detect the external hook all through when the line parity turns over.
4) Recall Circuit
• In the discrete LIU method, we used the recalling method using low cost photo coupler instead of using photo MOS relay
in order to initiate the recalling for handset hook off dialling after the power is turned on. In this case, the time break recall
was enabled by switching the power transistor of the telephone circuit using the secondary CPU control.
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