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PDF LM1872 Data sheet ( Hoja de datos )
| Número de pieza | LM1872 | |
| Descripción | Radio Control Receiver/Decoder | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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February 1989
LM1872 Radio Control Receiver Decoder
General Description
The LM1872 is a complete RF receiver decoder for radio
control applications The device is well suited for use at ei-
ther 27 MHz 49 MHz or 72 MHz in controlling various toys
or hobby craft such as cars boats tanks trucks robots
planes and trains The crystal controlled superhet design
offers both good sensitivity and selectivity When operated
in conjunction with the companion transmitter LM1871 it
provides four independent information channels Two of
these channels are analog pulse width modulated (PWM)
types while the other two are simple ON OFF digital chan-
nels with 100 mA drive capability Either channel type can
be converted to the other form through simple external cir-
cuitry such that up to 4 analog or up to 4 digital channels
could be created Few external parts are required to com-
plement the self-contained device which includes local os-
cillator mixer IF detector AGC sync output drivers and all
decoder logic on-chip
Features
Y Four independent information channels two analog and
two digital
Y Completely self-contained
Y Minimum of external parts
Y Operation from 50 kHz to 72 MHz
Y Highly selective and sensitive superhet design
Y Operates from four 1 5V cells
Y Excellent supply noise rejection
Y 100 mA digital output drivers
Y Crystal controlled
Y Interfaces directly with standard hobby servos
Applications
Y Toys and hobby craft
Y Energy saving remotely switched lighting systems
Y Burgler alarms
Y Industrial and consumer remote data links
Y IR data links
Y Remote slide projector control
Circuit Block and Connection Diagram
Dual-In-Line Package
Bottom View
Order Number LM1872N
See NS Package Number N18A
TL H 7912 – 1
C1995 National Semiconductor Corporation TL H 7912
RRD-B30M115 Printed in U S A
1 page  
Circuit Description
The following discussion is best understood by referring to
Figures 2 3 4 and 5
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 (tM in Figure 2 ) with each interval fol-
lowed by variable width pulses (tCH) so as to define multiple
variable time spans (tM a tCH) occurring in serial fashion
Synchronization is accomplished by allowing one of the
transmitted variable pulse widths (tSYNC) to exceed the du-
ration (t’SYNC) of a receiver-based timer thus allowing the
receiver to recognize this pulse for synchronization purpos-
es Taken in sequence this collection of pulses constitutes
a single frame period (tF)
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 )
FIGURE 2 RX Timing Waveforms
LM1871 TX
Pin Conditions
Transmitted Waveform
Pin 5 (CH A) Pin 6 (CH B)
TL H 7912 – 5
LM1872 RX
Binary
Digital Outputs
Pulse Count CH A CH B
OPEN
OPEN
TL H 7912 – 6
100
OFF OFF
GND
OPEN
TL H 7912 – 7
101
ON OFF
OPEN
GND
TL H 7912 – 8
110
OFF ON
GND
GND
TL H 7912 – 9
111
ON
FIGURE 3 Digital Channel Encoding and Decoding via Pulse Count Modulation
ON
5
5 Page 
Applications (Continued)
R1 Motor decoupling
R2 Sync timer R2 e t’SYNC R2 s 470k
0 7 C6
R3 Mixer decoupling
C1 LO bypass optional
C2 LO tank C2 e 22 pF 72 MHz
C3 Ant input tank C3 e 24 pF 72 MHz
C4 VBIAS bypass
C5 Motor decoupling
C6 Sync timer C6 e t’SYNC C6 s 0 5 mF
0 7 R2
C7 Mixer decouple 0 01 mF s C7 s 0 1 mF
C8 AGC
C9 IF bypass optional
C10 Va bypass 0 01 mF s C10 s 0 1 mF
C12 Ant input tank C12 e 160 pF 72 MHz
TL H 7912 – 15
L1 LO Coil
Toko 10k type (KENC) 4T 0 2 mH 72 MHz
L1 could be made a fixed coil if desired
T1 455 kHz mixer transformer
Toko 10 EZC type (RMC-502182) Qu e 110
Pin 1–2 82T pin 2–3 82T
Pin 1–3 164T pin 4–6 30T
T2 455 kHz IF transformer
Toko 10 EZC type (RMC-502503) Qu e 110
Pin 1–2 82T pin 2–3 82T
Pin 1–3 164T pin 4–6 8T
T3 Ant input transformer
Toko 10k type (KENC) 4T sec
2T pri of 0 2 mH 72 MHz
X1 5th overtone crystal parallel-mode 72 MHz
D1 Electrostatic discharge (ESD) protection
FIGURE 8 72 MHz Receiver Circuit
In a practical remote data link the transmitter could be bat-
tery operated and set up to transmit for brief intervals only in
order to save power The brief transmission could be used
to set or reset the digital output latches in the LM1872 and
or command new motor positions via the analog channels
After transmission the commands would be stored electri-
cally in the case of the digital channels and mechanically in
the case of the analog channels
As a final note if the case of D1 is connected to the anode
rather than the cathode the circuit of Figure 9b should be
used at the input to maintain electromagnetic shielding
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LM1872.PDF ] | |
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