LM1872N National Semiconductor, LM1872N Datasheet - Page 5

• Manufacturer Part Number: LM1872N
• Description: IC RECEIVER RADIO CTRL 4CH
• Manufacturer: National Semiconductor

Specifications of LM1872N

• Function: Receiver, Decoder
• Frequency: 27MHz, 49MHz, 72MHz
• Package / Case: 18-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM1872N; LM1872

Figures 2 3 4 and 5
Circuit Description
The following discussion is best understood by referring to
SYSTEM ENCODING AND DECODING SCHEME
For the transfer of analog information the LM1871 LM1872
system uses conventional pulse width modulation (PWM) In
applying this technique the RF carrier is interrupted for
short fixed intervals (t
lowed by variable width pulses (t
variable time spans (t
Synchronization is accomplished by allowing one of the
transmitted variable pulse widths (t
ration (t’
receiver to recognize this pulse for synchronization purpos-
es Taken in sequence this collection of pulses constitutes
a single frame period (t
Pin 5 (CH A)
SYNC
OPEN
OPEN
GND
GND
) of a receiver-based timer thus allowing the
Pin Conditions
FIGURE 3 Digital Channel Encoding and Decoding via Pulse Count Modulation
M
M
Pin 6 (CH B)
F
in Figure 2 ) with each interval fol-
)
a
OPEN
OPEN
GND
GND
t
CH
) occurring in serial fashion
CH
) so as to define multiple
SYNC
LM1871
) to exceed the du-
FIGURE 2 RX Timing Waveforms
Transmitted Waveform
TX
5
The LM1871 transmitter is equipped to transmit up to six
channels which the companion LM1872 receiver uses to
derive 2 analog and 2 digital channels The receiver de-
codes the demodulated RF waveform from the transmitter
by negative edge triggering a cascade of three binary divid-
ers called the A B and C toggle flip-flops ( Figure 4 ) By
‘‘examining’’ all three flip-flop outputs simultaneously up to
6 unique channel time intervals could be identified and re-
covered Only the first two channels are actually decoded
however and outputted by the receiver the rest being used
for identification of two digital (ON OFF) channels In pass-
ing digital information a pulse count modulation scheme is
used whereby different quantities of channel pulses are
transmitted by varying the number of fixed width channels
following the two variable width analog channels 1 and 2
(see Figure 3 )
TL H 7912 – 6
TL H 7912 – 7
TL H 7912 – 8
TL H 7912 – 9
Pulse Count
Binary
100
101
110
111
LM1872
Digital Outputs
CH A
OFF
OFF
ON
ON
TL H 7912 – 5
RX
CH B
OFF
OFF
ON
ON