Multitone RPR 583, Technical Manual

Page: 41 / 91

RPR 583
TM1212 Issue 1 Page 3 - 9
3.3.7 Display Illumination
One miniature lamp is used to illuminate the LCD display. The lamp is selected ON
or OFF using the buttons on the front panel. The ‘Lamp ON/OFF’ signal, which
comes from pin 8 of the microprocessor, controls transistor TR2 in the lamp circuit.
3.3.8 Alerts
a) Audible Alert (Beep)
The transducer, SP401, and the driver circuits TR415 and TR416, are installed
on the radio board. The audible alert signal from IC3, pin 2 connects to TR415
through SK1/PL401 pin14. The alert can be selected ON or OFF using the
buttons on the front panel.
b) Vibrate Alert
The vibrate motor is operated by transistors TR3 and TR4 on the decoder
board. The vibrate alert signal from IC3, pin 7 connects to pin 1 of TR3. The
alert can be selected ON or OFF using the buttons on the front panel.
3.4 POWER SUPPLIES
The primary power supply for the unit is a single 1.5 volt, AAA battery (BAT1). The
supply from the battery (B+) connects directly to the lamp and vibrate motor circuits
that require relatively high currents. B+ also connects to the radio board through
SK1/PL401, pin 9 and to the voltage converter, IC6, on the decoder board.
IC6 and its associated components supply the +3.0 volts (VDD) for the unit. In
addition, the circuit charges the backup supply (BAT2) through resistor R6. Double
diode D2 provides isolation for the two circuits.
IC5 is configured to monitor Vdd and resets the decoder circuits if the voltage would
cause data corruption.
Transistor TR1, connected to pins 6 and 15 of IC3, detects the battery voltage. If
BAT1 is removed, the drop in B+ causes transistor TR1 to switch OFF which sets the
microprocessor to low-current mode. In this mode BAT2 supplies sufficient power
to keep the microprocessor and the SRAM operational for more than 5 minutes.
The 1 volt supply for the receiver circuits is provided by transistor TR406 and its
associated components. The circuit is a series regulator and is maintained within
specification by a control circuit in IC401.