User Guide

RH-21 Company Confidential
System Module Nokia Customer Care
Page 12  2004 Nokia Corporation. Issue 2 07/2004
The current for the LCD lights is limited by the resistor between the ISET pin of the LED
driver and ground. For the keyboard lights, there are resistors in parallel.
Vibra
Introduction
The vibra is located on D-cover and is connected by spring connectors on PWB. It is
located in the left bottom side of the engine.
Interfaces
The vibra is controlled by the PWM signal VIBRA from the UEM. With this signal, it is
possible to control both the frequency and pulse width of signal. Pulse width is used to
control current when the battery voltage changes. Frequency control makes it possible to
search for an optimum frequency to provide silent and efficient vibrating.
Audio Hardware
Earpiece
Introduction
The 13 mm speaker capsule that is used in DCT3 products is also used in RH-21.
The speaker is dynamic. It is very sensitive and capable of producing relatively high sound
pressure at low frequencies.
Microphone
Introduction
The microphone is an electret microphone with an omnidirectional polar pattern. It con-
sists of an electrically polarized membrane and a metal electrode which forms a capaci-
tor. Air pressure changes (i.e., sound) move the membrane, which cause voltage changes
across the capacitor. Becauce the capacitance is typically 2 pF, a FET buffer is needed
inside the microphone capsule for the signal generated by the capacitor. Because of the
FET, the microphone requires a bias voltage.
MIDI Speaker
Introduction
The speaker being used to generate MIDI ring tones is a 13mm SALT speaker. The SALT
speaker is mounted in the D-cover, kept in position by a double adhesive gasket that is
mounted on the front of SALT. The useful frequency range is approximately 340 Hz to
8KHz.