Barco SLM R12 Plus, Service Manual, Page: 44 / 281

7. IR Transmitter RC-5 Coded R763569
Backlight LED Drive
The transistor Q8 drives the 12 LED’s via their ballast resistors R30..R41. The On/Off status is imposed through R22 by IC1, output
RA2, which handles the switch-on criteria. When the Jack cable connection is installed, the transistor Q8 is driven by the saturated
transistor Q10 through R25, causing the backlight to be lit continuously.
Indicator LED driving
The transistor Q6 drives the LED D22 via the resistor R28. The latter needs to have a rather small value because the driving pulses
are very short. The transistor Q6 is connected to the unmodulated RC5 drive output, pin RA1 of IC1, and drives the LED D5 via the
resistor R13.
Jack cable connection
The IC1 also senses the backlight driving pin RA2 whether it is high already before it decides to switch on the backlight; if this is the
case, the address is reset to 0 and the modulated IR Output RA0 is blocked.
3.5mm Jack cable connection
The Zenerdiode Z1 and the diode D8 provide the necessary voltage drop from 9V to 3V (Projector supply voltage for the cable
connected Remote Control is 9V). The Zenerdiode Z3 limits this internal 3V to 5V maximum. The voltage drop across the zenerdiode
Z1 drives the transistor Q8 through the transistors Q11/Q10. The RC5 in formation is injected into the cable as current pulses driven
by the transistor Q9. The resistor R20 determines the amplitude of these current pulses that are drawn from the 9V, supply voltage
from the projector, where they are detected by a series resistor and further processed. The diode D8 takes care that the transistor
doesn’t discharge the decoupling capacitors C4 and C5.
42 R5976820 SLM R12+ PERFORMER 08/03/2005