Manufacturer Part NumberLM1872N
ManufacturerNational Semiconductor
LM1872N datasheet

Specifications of LM1872N

FunctionReceiver, DecoderFrequency27MHz, 49MHz, 72MHz
Package / Case18-DIP (0.300", 7.62mm)Lead Free Status / RoHS StatusContains lead / RoHS non-compliant
Other names*LM1872N
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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
Circuit Block and Connection Diagram
C 1995 National Semiconductor Corporation
TL H 7912
Four independent information channels two analog and
two digital
Completely self-contained
Minimum of external parts
Operation from 50 kHz to 72 MHz
Highly selective and sensitive superhet design
Operates from four 1 5V cells
Excellent supply noise rejection
100 mA digital output drivers
Crystal controlled
Interfaces directly with standard hobby servos
Toys and hobby craft
Energy saving remotely switched lighting systems
Burgler alarms
Industrial and consumer remote data links
IR data links
Remote slide projector control
Dual-In-Line Package
Bottom View
Order Number LM1872N
See NS Package Number N18A
February 1989
TL H 7912 – 1
RRD-B30M115 Printed in U S A

LM1872N Summary of contents

  • Page 1

    ... 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 Y Dual-In-Line Package Bottom View Order Number LM1872N See NS Package Number N18A February 1989 TL H 7912 – 1 RRD-B30M115 Printed ...

  • Page 2

    ... Absolute Maximum Ratings If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Supply Voltage Package Dissipation (Note 2) Voltage Pin Electrical Characteristics 25 C Test Circuit of Figure Parameter Conditions Supply Voltage Functional for V Supply Current ...

  • Page 3

    AC Electrical Characteristics Parameter Conditions Mixer Input Impedance Pin 5 to Pin 4 (See Curves) Mixer Output Impedance Pin 18 to GND IF Transconductance Pin 17 to Pin 15 (AGC Off) IF Input Impedance Pin 17 to GND IF Output ...

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    Typical Performance Characteristics IF Bandpass Response Test Circuit L1 Toko 10k type (KEN-4028 DZ Toko 10 EZC type (RMC 202313 NO Pin 1–2 131T pin 2–3 33T Pin 1–3 164T pin 4–6 5T (Continued) Equivalent ...

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    Circuit Description The following discussion is best understood by referring to Figures 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 ...

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    Circuit Description (Continued) FIGURE 4 Simplified Schematic Diagram External parts Depending on layout a small capacitance (10–47 pF) may be required across pins 2 and 3 to ensure oscillator start 7912 – 10 ...

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    Circuit Description (Continued) Thus either channels are transmitted to repre- sent the four possible codes that two digital channels repre- sent The receiver intrinsically counts channels with its de- coder flip-flops by responding to the ...

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    Circuit Description (Continued) and T3 This tank effectively keeps strong out-of-band sig- nals such as FM and TV broadcast from cross-modulating with the desired signal When operating at 49 MHz or 72 MHz CB interference is also effectively minimized Im- ...

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    Application Hints A typical application circuit for either 27 MHz or 49 MHz is shown in Figure 5 Using the recommended antenna input networks and driving the circuit through the antenna simula- tion network of Figure 6 a solid decoded ...

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    Application Hints (Continued) The digital channel output devices have significant drive ca- pability they can typically sink 100 mA and possess a 7 saturation resistance Through their emitters they can source 100 above ground for driving ...

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    Applications (Continued) R1 Motor decoupling t’ SYNC R2 Sync timer Mixer decoupling C1 LO bypass optional C2 LO tank MHz e C3 Ant input tank ...

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    Applications (Continued) R1 Load decoupling t R2 Sync timer R2 R2 470k Preamp decoupling R5 Photodiode decoupling C1 Photodiode decoupling C2 V bypass BIAS bypass C4 Load decoupling C5 IF bypass ...

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    Applications (Continued) EXPANSION TO FOUR ANALOG CHANNELS For those applications that require more than the two ana- log channels that are normally provided the LM1872 can easily be expanded to 4 channels with appropriate external circuitry This is accomplished by ...

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    Applications (Continued) b) Simple Decoding of Four Analog Channels with CMOS c) Low-Cost Decoding of Four Analog Channels with DTL FIGURE 10 Deriving Four Analog Channels Through the Use of an Auxiliary Decoder (Continued) FOUR SINGLE CHANNEL RECEIVERS DRIVEN FROM ...

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    Applications (Continued) a) Transmitter Receiver and Separated Channels Timing Diagram b) Simple Channel Separation with Two External Transistors FIGURE 11 Obtaining Four Independent Single Analog Channel Receivers from a Single Common Transmitter 7912 – ...

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    Applications (Continued) EXPANSION TO SIX ANALOG CHANNELS Still greater analog capacity can be obtained with an out- board auxiliary decoder The LM1872 a simple comparator and an 8-bit parallel-out serial shift register comprise a six analog channel receiver decoder (Figure ...

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    Applications (Continued) Where only one of the two available analog channels needs conversion to a digital format the LM555 approach offers simplicity combined with up to 150 mA of output drive (Fig- ure 14) The trailing edge of CH 1’s ...

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    Applications (Continued) BRIDGE DRIVING A MOTOR The two digital channels can be used to propel a car for- ward off and reverse without the need for a costly servo (Figure 16) The 100 mA digital output capability is used to ...

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    Applications (Continued) FIGURE 16 Digital Bridge Motor Drive a) Low Current Load FIGURE 17 Integrating a Digital Channel Output to Achieve Noise Immunity b) High Current Load 7912 – 7912 – 29 ...

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    ... National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications Molded Dual-In-Line Package (N) Order Number LM1872N NS Package Number N18A 2 A critical component is any component of a life ...