Philips FTL2.1E Service Manual page 132

EN 132 9. FTL2.1E, FTL2.2E
9.7.2 Block Diagram
The function diagram is shown in the next figure.
36.7 kHz
f
0
Microcontroller
PWM
Figure 9-7 Emitting and detecting diagram
Emitting phase
IR Transmission (fo)
The IR transmission is realised with diode D6080 (TSAL5300).
This IR emitting diode is modulated with a 36.7 kHz signal. This
frequency (fo) is the same as the carrier frequency of the
remote control system (RC5/6). The microcontroller IC7075
(87LPC760) generates a specific pattern: during one second
10 times 100 periods (T0= 1/f0) of the modulation signal is sent
with a duty cycle of 50%. A timer port of the microcontroller is
used to generate the 36.7 kHz
AGC of the transmission (PWM)
The Automatic Gain Control (AGC) allows managing the power
of the IR emitting diode according to the detected reflection
signal. The microcontroller generates a Pulse Width
Modulation (PWM) signal that will change as soon as there is a
reflection signal received by the RC5/6 system. If there is no
reflection signal detected, the power will increase (average
PWM signal tends to "0"). If a detection signal appears and
remains, the power of the IR diode will decrease (average
PWM signal tend to "1"). The average PWM signal is realised
with a RC filter.
The maximum power depends on the forward current (If) in the
IR diode. This current can be adjusted with the resistance
R3022: the higher this resistance, the lower the IR power.
During the start up of the Proximity sensor feature, a calibration
mode will adapt the power of the IR diode. It is clear that the
distance of the detection will decrease while the PWM signal
tends to "1".
If a fixed object is placed in front of the TV set, the power will
be adjusted and the detection zone will be limited from the TV
set until the object. A timer port of the microcontroller is used to
generate the PWM signal.
Detecting phase
IR detection (Reflection)
The IR detection is done via the existing remote control system
(RC5/6). This IR receiver system detects all signals that get a
carrier frequency of 36.7 kHz (f0). When a signal is detected,
the output of the RC5/6 system will go to "0".
For the proximity sensor, we use this detection process to
activate the LED signal. The microcontroller receives the
Circuit Descriptions, Abbreviation List, and IC Data Sheets
V
DD
I
f
V
R
DD
1
IR transmission
LED
R
C
GND GND
V
DD
V
DD
Rp
IR RC5
D
RC5
Reflection
GND
E_14620_014.eps
200804
detection signal coming from the reflection. There is a reflection
when the modulated pattern (sent through the IR transmitting
diode) hits an object or a person in the detection zone. The IR
receiver demodulates the pattern signal that is directly decoded
by the microcontroller. It is clear that the reflection will depend
on the colour and texture of the customers clothing, or the
object (table, chair...).
The figure shows the connection between the microcontroller
and the RC5/6 system. The input port (an interruption pin) of
the microcontroller is used for this.
Detection zone
The detection zone is defined when the IR diode power is at its
maximum (average PWM signal is "0").
The Proximity sensor is more sensitive with bright and
reflective clothes or surfaces. The detection zone is quite
directive and is limited to one side of the set. Therefore, a
divergence lens should be placed in front of the IR emitting
diode to increase the detection zone and /or the IR diode
orientation has to change on the main switch board.
Lighting phase
Fade in/out effect and current driver:
When the microcontroller detects a reflection signal, it will
switch on the blue LEDs located on the Top Control. The light
of the LED will increase gradually to full intensity (fade in
effect). This effect will take 1 s. The light will remain "on" during
6 s, then it will switch "off" gradually within 3 s (fade out effect).
The light can re-trigger if the microcontroller receives the
keyboard press information (as described in the "keyboard
press detection" paragraph).
The fade in/out effect is realised with a simple electronic circuit
(see following figure). The timing can be adjusted by changing
the value of the resistors R3031 and R3032.
VCC
Microcontroller
LED
36.7 kHz
GND
Figure 9-8 Fade in/out circuitry
A current driver circuit is used to power at least ten blue LEDs
(see next figure). This current driver can supply around 120 mA
thanks to the transistor TS7031.
Microcontroller
Fade in/out
LED
circuit
Figure 9-9 LED driver circuitry
Keyboard press detection
If the user manages to approach the set without activating the
sensor but presses any button on the Top Control, the blue light
will switch "on". If the user activates any button within the
lighting phase, the light stays on for another 6 s.
VCC
D1 R1
R2
Fade
D2 R2
C
GND GND
E_14620_016.eps
110504
VCC VCC
T
Fade
Dz
5V6
Blue LEDs
GND
Top Control
E_14620_017.eps
110504