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Infrared Remote Control Transmitter
PT2248
CONTINUOUS SIGNAL
P T 2248 K ey O n
/T X OU T
48 a
80 a 48 a
20 8a
48 a
80 a 48 a
2 Co mm and W or ds
P aus e
When any of the continuous keys is depressed, the above continuous signal transmits a repetitive
cycle of 2 command words and then a pause (with a pause duration of 208a) until the key is released.
If the key is released during code transmission, PT2248 will still continue to send out the last set of 2
command words and then the transmitting output stops. Please refer to the diagram below:
P T 2248 K ey O n
/T X O UT
48a
80a
48a
208a
48a
80a 48a
48a
80a
48a
2 Co mm and W or ds
P aus e
2 Co mm and W or ds
CARRIER WAVE
About 50 ~ 100mA current is normally applied through an infrared LED in order to extend the infrared
reaching distance. Therefore, reducing the time when the LED is ON leads to the reduction of power
consumption. On PT2248, when the signal is transmitting, each bit is switching by a carrier wave of 1/3
duty. Carrier frequency (fc) is dependent on the oscillation frequency (fosc) and is given by the
following formula:
fosc
a=
12
where: fc = 38KHz at fosc = 455KHz
Tr an s m it tin g S ig n a l
(Hz)
P u ls e M od u la te d
Tra n s mit t in g S ig na l
PT2248 V2.7
-9-
June, 2005
PTC [ PRINCETON TECHNOLOGY CORP ]
