Angelcare AC401 Circuit Description

CIRCUIT DESCRIPTION OF AC401
A. BABY UNIT

1. POWER SUPPLY

DC 7.5V from AC adapter or 6V battery is input and they are input to BU1 regulator to provide
main DC supply to the rest of circuit.
(4 pieces of AAA size alkaline batteries can be used to power up the unit instead of using AC
adapter.)

2. POWER AND NIGHTLIGHT SWITCHES

BSW1 is built to control power on/off of the unit.
BSW2 is built to turn on and off the night light (LED at the eye of angel).

3. MOVEMENT SENSOR PAD SENSITIVITY ADJUST

Movement vibration is input through SJ1 and the signal is filtered by active filter formed by SU1-A
and SU1-B op-amps. The filtered signal is input into pin 26 of CPU BU4 through SCN1-2 and
normal movement display is shown by BLED2 with tic sound from BBUZ1 which is located on the
microphone PCB. If movement signal is found abnormal or no vibration detected, alarm sound will
alert from BBUZ1. In addition, data will be sent to parent side for alerting alarm. SVR1 is used to
adjust a level what user wants for the application.

4. PAGE AND REGISTRATION BUTTON

Switch BSW3 is used as:
a. Press and release for paging parent unit.
b. Press and hold for 2 seconds for registration with parent unit in order to link up data
communication.

5. SOUND DETECT AND TRANSMISSION

Microphone BMIC1 collects surrounding sound and the signal is enlarged by BU2-A and BU2-B.
BU2-B output is also used for detecting level of input sound if it is large enough to turn on
transmission to parent unit.
BU4 CPU turns on audio MUTE switching transistor BQ3 for audio passing into RF module.
RF TX power is turned ON by switching transistors, BQ5 for TXVCC and BQ10 for VPA (power
amplifier DC) from BU4 control.

6. PILOT TONE SHAPER

Pilot tone shaper is formed by BR71,19,24,27 and BC37,39,40,41 which filters the signal from
CPU and forms the pilot tone into RF module.

7. DATA SHAPER

BQ68, BQ9 form a data shaper which regulates the data transmitted from parent unit, such as
commands to change operation modes and channel selection.

8. BATTERY DETECT AND LOW ALERT

While using alkaline battery, battery level is detected by voltage level detected at junction of BR43
and BR55. If battery is detected low, BLED3 will flash to alert user.