Table of Contents
Advertisement
Handset HSU–1
– HOOK switch ( REED relay )
– Voltage regulator
Earphone and microphone paths are controlled by Hook switch, which is
opened automatically, when the handset is lifted from the cradle. In the
cradle there is a magnet and in the handset there is a reed relay. Reed
relay controls audio switches. The earphone amplifier is differential type
and output is symmetrical. Volume is user controllable. Microphone is an
electret microphone (condensator type) with field effect transistor. It re-
quires a bias voltage above 2.0 Volts for normal operation. Bias voltage is
generated with suitable deviding resistors and transistor from regulated
8.5 V.
Earphone Amplifier
Earphone amplifier is of differential type. N2A and N2B are used to form a
differential amplifier with total amplification of 26 dB. Ear signal is fed to
DG–1 module via connector X1 pin 8. L2 and C3 are used to improve
EMI characteristics. Capacitor C5 blocks DC of the signal analog switch
N3A ( 74HC4066 ) switches Ear signal during ON HOOK state. Capacitor
C24 is used to modificate frequency characteristics of Ear signal at higher
frequencies. The gain of ear piece amplifier is set by resistors R14, R15,
R16 and R17, R18. R19 is used to form side tone. Ear piece capsule is
connected to the PC–board via connector X2. Resistors R20, R23, R26
and trimmer R22 attenuates Ear signal. Attenuation is about 20 dB when
the trimmer is at minimum position.
Microphone Amplifier
Transistor V1 supplies bias voltage to Microphone. Bias voltage is filtered
by C20, C11,C12, C14 and resistors R12, R13. Bias voltage is fed to mi-
crophone connector X3 via resistor R11. Bias voltage at connector X3 pin
1 is about 3.4 volt. Capacitor C10 blocks DC voltage of the Mic signal. Mic
signal is amplified by N2D ( TL074ID ) Resistors R5, R7, R8, R9, R10 and
capacitor C7, C9, C15 are used to filter Mic signal. Capacitor C8, C16,
C23 are used to improve EMI characteristics. Gain of Mic amplifier is set
by R7 and R24. Mic signal is fed to Ear amplifier via resistor R19 to form
side tone signal. Mic signal is fed to connector X1 pin 7 via analog switch
N3B ( 74HC4066 ). Capacitor C19 blocks DC voltage of the signal.
HOOK Operation
Both Mic signal and Ear signal are controlled by analog switches
74HC4066. Audio channels are open when Reed relay S1 is not acti-
vated. S1 is connected to Enable inputs of analog switches and R5 is a
pull– up resistor to open analog switches when S1 is open. When S1 is
activated ( is closed ) analog switches are opened. Resistor R21 and ca-
pacitor C21 forms a filter to improve EMI characteristics.
Page – 6
After Sales
Technical Documentation
Original 50/96
Hide quick links:
Advertisement
Table of Contents
