W-Linx Technology TXE-418-KH User's Manual
Contents
1. e lt 1 Word Encoder E Data Out e 3Words gt ja Tanemitted Continuously 3 Words gt j 214 Clocks Transmission Enabled K 2 Words gt Decoder VT ee a t Check wa e Check gt Decoder C Data Out i gt ja 1 2 Clock Time gt 1 2 Clock Time Figure 9 Encoder Decoder Timing Diagram SETTING THE TRANSMITTER ADDRESS The module provides ten tri state address lines This allows for the formation of up to 59 049 310 unique transmitter receiver relationships Tri state means that the address lines have three distinct states high low or floating These pins may be hardwired or configured via a microprocessor DIP switch or jumpers The receivers address line states must match the transmitters exactly for a transmission to be recognized If the transmitted address does not match the receiver s local address then the receiver will take no action Page 6 POWER SUPPLY REQUIREMENTS The module does not have an internal voltage regulator therefore it requires a clean well regulated power source While it is preferable to power the unit from a battery it can also be operated from a power supply as long as noise is less than 20mV Power supply noise can affect the transmitter modulation therefore providing a clean power supply for the module should be a high priority during design A 10Q resistor in series with the supply followed by a 10pF tantalum c2. TXE 315 KH TXE 418 KH TECHNOLOGIES _ XE 433 KH DDI Gens KH SERIES TRANSMITTER ENCODER DATA GUIDE DESCRIPTION The KH Series is ideally suited for volume use in OEM applications such as remote control and command and keyless entry Housed in a ee compact SMD package it combines a highly S LINX optimized RF transmitter with an on board RF TRANSMITTER ENCODER encoder When paired with a matching KH TE aH Series receiver decoder module a reliable ad Ail wireless link is formed capable of transferring the status of 8 parallel inputs over distances in excess of 300 feet Ten tri state address lines provide 59 049 319 addresses for security and uniqueness No external RF components are required except an antenna making integration straightforward Figure 1 Package Dimensions FEATURES E Low cost E Ultra low power consumption E On board encoder E Compact SMD package E 8 parallel binary inputs E Stable SAW based architecture m 310 addresses for security and E Adjustable output power uniqueness E Transmit enable line E No external RF components E No production tuning required APPLICATIONS INCLUDE m Remote Control Command ORDERING INFORMATION E Keyless Entry PART DESCRIPTION E Garage Gate Openers TXE 315 KH Transmitter 315MHz E Lighting Control TXE 418 KH Transmitter 418MHz E Call Systems TXE 433 KH Transmitter 433MHz E Home Industrial Automation RXD 315 KH Receiver 315MHz
3. a highly reliable RF link capable of transferring control or command data over line of sight distances in excess of 300 feet is formed The module accepts up to 8 parallel inputs such as switches or contact closures and provides ten tri state address lines for security and creation of 59 049 310 unique transmitter receiver relationships The KH s compact surface mount package integrates easily into existing designs and is friendly to hand production or automated assembly Address Inputs A0 AQ SAW Lace a 1 Oscillator Parallel Figure 6 KH Series Transmitter Pinout Top View cata AN Divider _ eosc inputs ey a ae DO D7 Counter gt TRI Detect Keyed Output PIN DESCRIPTIONS WS Buffer lt Sync Pin Name Description Output Isolation RF Amplifier amp Filter Level Adjust This line can be used to adjust the output 1 GND LADy Power level of the transmitter Connecting to GND will give RF STAGE ENCODER STAGE the highest output while placing a resistor to GND will Figure 7 KH Series Transmitter Block Diagram lower the output level Data Input Lines When TE goes high the module will THEORY OF OPERATION _ _ _ _ 2 3 DO D1 encode the state of these lines for transmission Upon The KH Series transmitter operation is straightforward When the Tr
4. E Fire Security Alarms RXD 418 KH Receiver 418MHz E Remote Status Monitoring RXD 433 KH Receiver 433MHz Wire Elimination EVAL KH Basic Evaluation Kit 315 418 Standard 433 92MHz Transmitters are supplied in tubes of 20 pcs Revised 10 12 06 ELECTRICAL SPECIFICATIONS Parameter Designation Typical POWER SUPPLY Operating Voltage Supply Current Power Down Current TRANSMITTER SECTION Transmit Frequency Range TXE 315 KH TXE 418 KH TXE 433 KH Center Frequency Accuracy Output Power Harmonic Emissions TXE 315 KH TXE 418 KH TXE 433 KH ANTENNA PORT RF Output Impedance ENCODER SECTION 50 ABSOLUTE MAXIMUM RATINGS Supply Voltage Voc Any Input or Output Pin Operating Temperature Storage Temperature Soldering Temperature NOTE Exceeding any of the limits of this section may lead to permanent 6 0 VDC Voc VDC 70 C 85 C 225 C for 10 seconds damage to the device Furthermore extended operation at these maximum ratings may reduce the life of this device PERFORMANCE DATA These performance parameters are based on module operation at 25 C from a 3 0VDC supply unless otherwise noted Figure 2 illustrates the connections necessary for testing and operation It is recommended all ground pins be connected to the Data Length 26 bits 3x ground plane Average Data Duty Cycle 50 Encoder Oscillator Data Input Logic Low TYPICAL PERFORMANCE GRAPHS Logic High M
5. and cosmetic requirements of the product You may wish to review Application Note AN 00500 Antennas Design Application Performance ANTENNA SHARING In cases where a transmitter and receiver module are combined to form a transceiver VoD it is often advantageous to share a single moue otur E a antenna To accomplish this an antenna i ne I switch must be used to provide isolation L lee between the modules so that the full aw A transmitter output power is not put on the sensitive front end of the receiver There are a wide variety of antenna switches that are cost effective and easy to use Among Figure 18 Typical Antenna Switch the most popular are switches from Macom and NEC Look for an antenna switch that has high isolation and low loss at the desired frequency of operation Generally the Tx or Rx status of a switch will be controlled by a product s microprocessor but the user may also make the selection manually In some cases where the characteristics of the Tx and Rx antennas need to be different or antenna switch losses are unacceptable it may be more appropriate to utilize two discrete antennas Select Page 14 Optimum performance will be obtained In some applications it is advantageous to GENERAL ANTENNA RULES The following general rules should help in maximizing antenna performance 1 Proximi
6. cute ENVIRONMENTAL Operating Temperature Range Figure 2 Test Basic Application Circuit ith LADI tied tb grouhd Table 1 KH Series Transmitter Electrical Specifications h LADJ tied to ground Notes 1 Current draw with 50 mark space ratio s f 2 Into a 50Q load reel eee 3 With 430Q resistor on LADJ ie ela on LADI 4 Characterized but not tested 25 30 35 40 45 5 0 Supply Current mA With 4300 resistor O NWAUMDNWO 25 30 35 40 45 50 Supply Voltage V Supply Voltage V Figure 3 Supply Current vs Supply Voltage Figure 4 Output Power vs Supply Voltage CAUTION This product incorporates numerous static sensitive components Always wear an ESD wrist strap and observe proper ESD handling procedures when working with this device Failure to observe this precaution may result in module damage or failure Output Power dBm 51 100 150 200 240 300 360 430 510 560 620 680 750 820 910 1 1K LADJ Pin Resistor Value Q Figure 5 Output Power vs LADJ Resistor Page 2 Page 3 PIN ASSIGNMENTS MODULE DESCRIPTION The KH Series transmitter encoder module combines a high performance 1 p LADJ GND ANT G 24 Surface Acoustic Wave SAW based transmitter with an on board encoder When combined with a Linx KH Series receiver decoder
7. is also suitable for use with the Linx OEM function receivers These receivers are FCC certified making product introduction extremely quick Information on these products can be found on the Linx website at www linxtechnologies com Page 9 BOARD LAYOUT GUIDELINES If you are at all familiar with RF devices you may be concerned about specialized board layout requirements Fortunately because of the care taken by Linx in designing the modules integrating them is very straightforward Despite this ease of application it is still necessary to maintain respect for the RF stage and exercise appropriate care in layout and application in order to maximize performance and ensure reliable operation The antenna can also be influenced by layout choices Please review this data guide in its entirety prior to beginning your design By adhering to good layout principles and observing some basic design rules you will be on the path to RF success The adjacent figure shows the suggested GROUND PLANE PCB footprint for the module The actual pad ON LOWER LAYER dimensions are shown in the Pad Layout section of this manual A ground plane as large as possible should be placed on a lower layer of your PC board opposite the module This ground plane can also be critical to the performance of your antenna which will be discussed later There should not be any ground or traces under the module on the same layer as the module just bare PCB Figure 12 Sugg
8. of their small size They offer a preferable alternative to the often problematic printed antenna Page 16 www linxtechnologies com NTENNA FACTOR ONLINE RESOURCES TECHNOLOGIES e Latest News e Data Guides e Application Notes e Knowledgebase e Software Updates If you have questions regarding any Linx product and have Internet access make www linxtechnologies com your first stop Our website is organized in an intuitive format to immediately give you the answers you need Day or night the Linx website gives you instant access to the latest information regarding the products and services of Linx It s all here manual and software updates application notes a comprehensive knowledgebase FCC information and much more Be sure to visit often www antennafactor com The Antenna Factor division of Linx offers a diverse array of antenna styles many of which are optimized for use with our RF modules From innovative embeddable antennas to low cost whips domes to Yagis and even GPS Antenna Factor likely has an antenna for you or can design one to meet your requirements ONNECTOR CITY THE VALUE OF CONNECTIONS www connectorcity com Through its Connector City division Linx offers a wide selection of high quality RF connectors including FCC compliant types such as RP SMAs that are an ideal match for our modules and antennas Connector City focuses on high volume OEM requireme
9. these instances a designer must make the best use ofthe Figure 20 Dipole Antenna area available to create as much ground plane as possible in proximity to the base of the antenna In cases where the antenna is remotely located or the antenna is not in close proximity to a circuit board ground plane or grounded metal case a metal plate may be used to maximize the antenna s performance Remove the antenna as far as possible from potential interference sources Any frequency of sufficient amplitude to enter the receiver s front end will reduce system range and can even prevent reception entirely Switching power supplies oscillators or even relays can also be significant sources of potential interference The single best weapon against such problems is attention to placement and layout Filter the module s power supply with a high frequency bypass capacitor Place adequate ground plane under potential sources of noise to shunt noise to ground and prevent it from coupling to the RF stage Shield noisy board areas whenever practical place the module and antenna away from the main equipment This can avoid interference CSE problems and allows the antenna to be CABUNG RINE oriented for optimum performance Always use MAY BE NEEDED 50Q coax like RG 174 for the remote feed Figure 21 Remote Ground Plane Page 15 COMMON ANTENNA STYLES There are literally hundreds of antenna styles and variations that can be employed w
10. ansmit 7 12 receipt of a valid transmission the receiver decoder will Enable TE line is taken high the on board encoder IC is activated The encoder replicate these lines on its output lines detects the logic states of the data and address lines These states are formatted into a 3 word transmission which continues until the TE line is taken low The encoder creates a serial data packet that is used to modulate the transmitter The transmitter section is based on a simple but highly optimized architecture that achieves a high fundamental output power with low harmonic content This Transmit Enable Line When this line goes high the ensures that most approval standards can be met without external filter TE module will encode the states of the address and data lines components The KH Series transmitter is exceptionally stable over variations in into a packet and transmit the packet three times time temperature and physical shock as a result of the precision SAW device that is incorporated as the frequency reference Address Lines The State oe these lines must match the The transmitted signal may be received by any Linx KH Series receiver decoder 13 22 A0 A9 state of the receivers address lines inorder fora module or Linx LC or LR Series receiver combined with the appropriate decoder transmission to be accepted IC Once data is received it is decoded using a decoder IC or custom microcontroller The transmitted address bits are checked agains
11. apacitor from Vcc to ground will help in cases where the quality of supply power is poor These values may need to be adjusted depending on the noise present on the supply line DATA INPUTS When the Transmit Enable TE line goes high the states of the eight data input lines are recorded and encoded for transmission The data lines are tri state which means that they can be high low or floating though the decoder will interpret the floating state as a low This feature means that the data lines do not require pull up or pull down resistors The states of the data lines can be set by switches jumpers microcontrollers or hardwired on the PCB Figure 10 Supply Filter The encoder will send the states of the address and data lines three times If the TE line is still high it will begin the cycle again This means that the states of the data lines are refreshed with each cycle so the data lines can be changed without having to pull TE low There can be up to a 150mS lag in response as the transmitter finishes one cycle then refreshes and starts over ENABLING TRANSMISSION The module s Transmit Enable TE line controls transmission status When taken high the module initiates transmission which continues until the line is pulled low or power to the module is removed In some cases this line will be wired permanently to Vcc and transmission controlled by switching Vgc to the module This is particularly useful in applications where
12. applicable to this module are contained in Volume 0 19 It is strongly recommended that a copy be obtained from the Government Printing Office in Washington or from your local government bookstore Excerpts of applicable sections are included with Linx evaluation kits or may be obtained from the Linx Technologies website www linxtechnologies com In brief these rules require that any device that intentionally radiates RF energy be approved that is tested for compliance and issued a unique identification number This is a relatively painless process Linx offers full EMC pre compliance testing in our HP Emco equipped test center Final compliance testing is then performed by one of the many independent testing laboratories across the country Many labs can also provide other certifications that the product may require at the same time such as UL CLASS A B etc Once your completed product has passed you will be issued an ID number that is to be clearly placed on each product manufactured Questions regarding interpretations of the Part 2 and Part 15 rules or measurement procedures used to test intentional radiators such as Linx RF modules for compliance with the technical standards of Part 15 should be addressed to Federal Communications Commission Equipment Authorization Division Customer Service Branch MS 1300F2 7435 Oakland Mills Road Columbia MD 21046 Phone 301 725 1585 Fax 301 344 2050 E Mail labinfo fcc gov Internationa
13. are critically dependent upon the antenna While adequate antenna performance can often be obtained by trial and error methods antenna design and matching is a complex task A professionally designed Figure 17 Linx Antennas antenna such as those from Linx will help ensure maximum performance and FCC compliance Linx transmitter modules typically have an output power that is slightly higher than the legal limits This allows the designer to use an inefficient antenna such as a loop trace or helical to meet size cost or cosmetic requirements and still achieve full legal output power for maximum range If an efficient antenna is used then some attenuation of the output power will likely be needed This can easily be accomplished by using the LADJ line or a T pad attenuator For more details on T pad attenuator design please see Application Note AN 00150 A receiver antenna should be optimized for the frequency or band in which the receiver operates and to minimize the reception of off frequency signals The efficiency of the receiver s antenna is critical to maximizing range performance Unlike the transmitter antenna where legal operation may mandate attenuation or a reduction in antenna efficiency the receivers antenna should be optimized as much as is practical It is usually best to utilize a basic quarter wave whip until your prototype product is operating satisfactorily Other antennas can then be evaluated based on the cost size
14. ested PCB Layout a During prototyping the module should be soldered to a properly laid out circuit board The use of prototyping or perf boards will result in horrible performance and is strongly discouraged No conductive items should be placed within 0 15in of the module s top or sides Do not route PCB traces directly under the module The underside of the module has numerous signal bearing traces and vias that could short or couple to traces on the product s circuit board The module s ground lines should each have their own via to the ground plane and be as short as possible AM OOK receivers are particularly subject to noise The module should as much as reasonably possible be isolated from other components on your PCB especially high frequency circuitry such as crystal oscillators switching power supplies and high speed bus lines Make sure internal wiring is routed away from the module and antenna and is secured to prevent displacement The power supply filter should be placed close to the module s Vgc line In some instances a designer may wish to encapsulate or pot the product Many Linx customers have done this successfully however there are a wide variety of potting compounds with varying dielectric properties Since such compounds can considerably impact RF performance it is the responsibility of the designer to carefully evaluate and qualify the impact and suitability of such material
15. he antenna should be kept as short as possible Width Height W a A simple trace is suitable for runs up to 1 8 inch for antennas with wide bandwidth characteristics For longer runs or to avoid detuning narrow bandwidth antennas such as a helical use a 50 ohm coax or 50 ohm microstrip 5 transmission line as described in the following section Page 10 Page 11 PAD LAYOUT AUTOMATED ASSEMBLY The following pad layout diagram is designed to facilitate both hand and For high volume assembly most users will want to auto place the modules The automated assembly modules have been designed to maintain compatibility with reflow processing techniques however due to the their hybrid nature certain aspects of the assembly process are far more critical than for other component types vet te Following are brief discussions of the three primary areas where caution must be observed 0 610 Reflow Temperature Profile The single most critical stage in the automated assembly process is the reflow BERBER eee 0 070 stage The reflow profile below should not be exceeded since excessive 7 temperatures or transport times during reflow will irreparably damage the 0 100 modules Assembly personnel will need to pay careful attention to the oven s profile to ensure that it meets the requirements necessary to successfully reflow all components while still remaining within the limits mandated by the modules PRODUCTION GUIDELINES The figure be
16. it is difficult to recommend one y a z i CONSULT LINX REGARDING particular design path but most projects follow steps ANTENNA Ey DEION similar to those shown at the right LAY OUT BOARD o a 5 Yy In reviewing this sample design path you may SEND PRODUCTION READY PROTOTYPE TO LINX notice that Linx offers a variety of services such as FOR EMC PRESCREENING antenna design and FCC prequalification that are ee ESC unusual for a high volume component manufacturer ee E These services along with an exceptional level of SEND TO PART 15 technical support are offered because we recognize that RF is a complex science requiring the highest B a caliber of products and support Wireless Made COMMENCE SELLING PRODUCT Simple is more than just a motto it s our commitment By choosing Linx as your RF partner and taking advantage of the resources we offer you will not only survive implementing RF you may even find the process enjoyable HELPFUL APPLICATION NOTES FROM LINX It is not the intention of this manual to address in depth many of the issues that should be considered to ensure that the modules function correctly and deliver the maximum possible performance As you proceed with your design you may wish to obtain one or more of the following application notes which address in depth key areas of RF design and application of Linx products These applications notes are available online at www linxtechnologies com or by contacti
17. ith Linx RF modules Following is a brief discussion of the styles most commonly utilized Additional antenna information can be found in Linx Application Notes AN 00100 AN 00140 and AN 00500 Linx antennas and connectors offer outstanding performance at a low price Whip Style A whip style antenna provides outstanding overall performance and stability A low cost whip is can be easily fabricated from a wire or rod but most designers opt for the consistent performance and cosmetic appeal of a professionally made model To meet this need Linx offers a wide variety of straight and reduced height whip style antennas in permanent and connectorized mounting styles The wavelength of the operational frequency determines an on antenna s overall length Since a full wavelength is often quite 234 long a partial 1 2 or 1 4 wave antenna is normally employed L F Its size and natural radiation resistance make it well matched to Meiz Linx modules The proper length for a straight 1 4 wave can be Where easily determined using the adjacent formula It is also possible L length in feet of to reduce the overall height of the antenna by using a helical quarter wave length winding This reduces the antenna s bandwidth but is a great F operating frequency ih megahen way to minimize the antenna s physical size for compact applications This also means that the physical appearance is not always an indicator of the antenna s frequenc
18. izing the KH Series transmitter When a key is pressed on the transmitter a corresponding line on the receiver goes high A schematic for the receiver decoder circuit may be found in the KH Series Receiver Data Guide These circuits are implemented in the KH Series Basic Evaluation kit They can be easily modified for custom applications and clearly demonstrate the ease of using the KH Series modules for remote control applications GND LADJ Do D1 GND VCC TE Sjef Noja D2 D3 o j IN Joa jo a Jo v SW DIP 10 D4 D5 D6 D7 TXE xxx KH CR2032 3V LITHIUM Figure 11 Basic Remote Control Transmitter The ten position DIP switch is used to set the address to either ground or floating Since the floating state is a valid state no pull up resistors are needed The data lines are pulled high by momentary pushbuttons Since the floating state is interpreted as a low by the decoder no pull down resistors are needed Diodes are used to pull the TE line high when any data line goes high while isolating the data lines from each other This will make the transmitter send data when any button is pressed without affecting any of the other data lines The KH Series transmitter encoder module
19. l approvals are slightly more complex although Linx modules are designed to allow all international standards to be met If you are considering the export of your product abroad you should contact Linx Technologies to determine the specific suitability of the module to your application All Linx modules are designed with the approval process in mind and thus much of the frustration that is typically experienced with a discrete design is eliminated Approval is still dependent on many factors such as the choice of antennas correct use of the frequency selected and physical packaging While some extra cost and design effort are required to address these issues the additional usefulness and profitability added to a product by RF makes the effort more than worthwhile Page 18 Adding an RF stage brings an exciting new dimension to any product It also means that additional effort and commitment will be needed to bring the product successfully to market By utilizing premade RF modules such as the LR Series the design and approval process is greatly simplified It is still important however to have an objective view of the steps necessary to ensure a successful RF integration Since the capabilities of each customer ACHIEVING A SUCCESSFUL RF IMPLEMENTATION DECIDE TO UTILIZE RF RESEARCH RF OPTIONS ORDER EVALUATION KIT S TEST MODULE S WITH BASIC HOOKUP CHOOSE LINX MODULE INTERFACE TO CHOSEN CIRCUIT AND DEBUG vary widely
20. l wick underneath the module providing reliable attachment Tack one module corner first and then work around the device taking care not to exceed the times listed below Since some internal module components may reflow along with the components placed on the board being assembled it is imperative that the modules not be subjected to shock or vibration during the time solder is liquid Should a shock be applied some internal components could be lifted from their pads causing the module to not function properly _ Absolute Maximum Solder Times _ ila The modules are wash resistant but are not hermetically sealed Linx Hand Solder Temp TX 225 C for 10 Seconds recommends wash free manufacturing however the modules can be subjected Hand Solder Temp RX 225 C for 10 Seconds to a wash cycle provided that a drying time is allowed prior to applying electrical power to the modules The drying time should be sufficient to allow any moisture Recommended Solder Melting Point 180 C that may have migrated into the module to evaporate thus eliminating the Reflow Oven 220 C Max See adjoining diagram potential for shorting damage during power up or testing If the wash contains contaminants the performance may be adversely affected even after drying Page 12 Page 13 ANTENNA CONSIDERATIONS The choice of antennas is a critical and often overlooked design consideration The range performance and legality of an RF link
21. low shows the recommended reflow oven profile for the modules Figure 14 Recommended PCB Layout The modules are housed in a hybrid SMD package that supports hand or Ideal Curve Forced Air Reflow Profile automated assembly techniques Since the modules contain discrete Limit Curve components internally the assembly procedures are critical to ensuring the reliable function of the modules The following procedures should be reviewed with and practiced by all assembly personnel HAND ASSEMBLY Pads located on the bottom of the module are the primary mounting Soldering Iron surface Since these pads are Tip inaccessible during mounting castellations that run up the side of the module have been provided to facilitate solder wicking to the module s underside This allows for very quick hand soldering for PCB Pads Castellations prototyping and small volume production Figure 15 Soldering Technique Figure 16 Maximum Reflow Profile Reflow Zorie O amp g g w g D 2 E oO He lt SoakZone 20 40 Sec i i 2 Minutes Max i Preheat Zone i 2 2 3 Minutes Cooling 150 180 210 240 270 300 330 360 Time Seconds If the recommended pad guidelines have been followed the pads will protrude Shock During Reflow Transport slightly past the edge of the module Use a fine soldering tip to heat the board pad and the castellation then introduce solder to the pad at the module s edge The solder wil
22. ng the Linx literature department NOTE APPLICATION NOTE TITLE AN 00100 RF 101 Information for the RF Challenged Typical Steps For Implementing RF Considerations For Operation Within The 260 470MHz Band AN 00130 Modulation Techniques For Low Cost RF Data Links AN 00140 The FCC Road Part 15 From Concept To Approval AN 00150 Use and Design of T Attenuation Pads AN 00160 Considerations For Sending Data Over a Wireless Link AN 00300 Addressing Linx OEM Products AN 00500 Antennas Design Application Performance Page 19 TECHNOLOGIES EA WIRELESS MADE SIMPLE U S CORPORATE HEADQUARTERS LINX TECHNOLOGIES INC 159 ORT LANE MERLIN OR 97532 PHONE 541 471 6256 FAX 541 471 6251 www linxtechnologies com Disclaimer Linx Technologies is continually striving to improve the quality and function of its products For this reason we reserve the right to make changes without notice The information contained in this Data Guide is believed to be accurate as of the time of publication Specifications are based on representative lot samples Values may vary from lot to lot and are not guaranteed Linx Technologies makes no guarantee warranty or representation regarding the suitability or legality of any product for use in a specific application None of these devices is intended for use in applications of a critical nature where the safety of life or property is at risk The user assumes full liability for the use of
23. nts which allows standard and custom RF connectors to be offered at a remarkably low cost LEGAL CONSIDERATIONS NOTE Linx RF modules are designed as component devices that require external components to function The modules are intended to allow for full Part 15 compliance however they are not approved by the FCC or any other agency worldwide The purchaser understands that approvals may be required prior to the sale or operation of the device and agrees to utilize the component in keeping with all laws governing its use in the country of operation When working with RF a clear distinction must be made between what is technically possible and what is legally acceptable in the country where operation is intended Many manufacturers have avoided incorporating RF into their products as a result of uncertainty and even fear of the approval and certification process Here at Linx our desire is not only to expedite the design process but also to assist you in achieving a clear idea of what is involved in obtaining the necessary approvals to legally market your completed product In the United States the approval process is actually quite straightforward The regulations governing RF devices and the enforcement of them are the responsibility of the Federal Communications Commission FCC The regulations are contained in Title 47 of the Code of Federal Regulations CFR Title 47 is made up of numerous volumes however all regulations
24. product in such applications Under no conditions will Linx Technologies be responsible for losses arising from the use or failure of the device in any application other than the repair replacement or refund limited to the original product purchase price 2006 by Linx Technologies Inc The stylized Linx logo Linx Wireless Made Simple CipherLinx and the stylized CL logo are the trademarks of Linx Technologies Inc Printed in U S A
25. r potential sources of noise must be approached with care Comparing your own design with a Linx evaluation board can help to determine if and at what level design specific interference is present External interference can manifest itself in a variety of ways Low level interference will produce noise and hashing on the output and reduce the link s overall range High level interference is caused by nearby products sharing the same frequency or from near band high power devices It can even come from your own products if more than one transmitter is active in the same area It is important to remember that only one transmitter at a time can occupy a frequency regardless of the coding of the transmitted signal This type of interference is less common than those mentioned previously but in severe cases it can prevent all useful function of the affected device Although technically it is not interference multipath is also a factor to be understood Multipath is a term used to refer to the signal cancellation effects that occur when RF waves arrive at the receiver in different phase relationships This effect is a particularly significant factor in interior environments where objects provide many different signal reflection paths Multipath cancellation results in lowered signal levels at the receiver and thus shorter useful distances for the link Page 8 TYPICAL APPLICATIONS Below is an example of a basic remote control transmitter util
26. s MICROSTRIP DETAILS A transmission line is a medium whereby RF energy is transferred from one place to another with minimal loss This is a critical factor especially in high frequency products like Linx RF modules because the trace leading to the module s antenna can effectively contribute to the length of the antenna changing its resonant bandwidth In order to minimize loss and detuning some form of transmission line between the antenna and the module should be used unless the antenna can be placed very close lt 1 8in to the module One common form of transmission line is a coax cable another is the microstrip This term refers to a PCB trace running over a ground plane that is designed to serve as a transmission line between the module and the antenna The width is based on the desired characteristic impedance of the line the thickness of the PCB and the dielectric constant of the board material For standard 0 062in thick FR 4 board material the trace width would be 111 mils The correct trace width can be calculated for other widths and materials using the information below Handy software for calculating microstrip lines is also available on the Linx website www linxtechnologies com V14 12d W 60 Ww eIn V Ee W 4d 1207 VE 1 393 0 667 d E Dielectric constant of PCB material Figure 13 Microstrip Formulas Effective Dielectric Characteristic The trace from the module to t
27. t the address settings of the receiving device If a match is confirmed the decoder s outputs Analog Sreuna are set to replicate the transmitter s inputs Page 4 Page 5 ENCODER OPERATION The KH Series transmitter internally utilizes the HT640 encoder from Holtek The Poweron encoder begins a three word transmission cycle when the Transmission Enable line TE is pulled high This cycle will repeat itself for as long as the TE line is held high Once TE falls low the encoder output completes its final cycle and then stops as shown in the Encoder Decoder Timing diagram When a transmission enable signal Yes is applied the encoder scans and transmits 3 Data Words the status of the 10 bits of the address code Transmitted and the 8 bits of the data serially in the order AO to A9 DO to D7 The status of each address data pin can be individually preset to logic high low or floating The floating state on the data input wee is interpreted as logic low by the decoders 3 Data Words since the decoder output only has two Transmitted 3 Continuously states The address pins are usually set to transmit particular security codes by DIP switches or PCB wiring while the data is Figure 8 Encoder Flowchart selected using push buttons or electronic switches The floating state allows the KH transmitter to be used without pull up or pull down resistors on the data and address input lines Encoder Transmit M o O Enable
28. the module powers up and sends a transmission only when a button is pressed on the remote USING LADJ The LADJ line allows the transmitters output power to be easily adjusted for range control lower power consumption or to meet legal requirements This is done by placing a resistor between GND and LADJ When LADJ is connected directly to GND the output power will be at its maximum Placing a resistor will lower the output power by up to 7dB as shown on Page 3 of this data guide This is very useful during FCC testing to compensate for antenna gain or other product specific issues that may cause the output power to exceed legal limits A variable resistor can be used so that the test lab can precicely adjust the output power to the maximun level allowed by law The resistor s value can be noted and a fixed resistor substituted for final testing Even in designs where attenuation is not anticipated it is a good idea to place a resistor pad connected to LADJ and GND so that it can be used if needed Page 7 PROTOCOL GUIDELINES While many RF solutions impose data formatting and balancing requirements Linx RF modules do not encode or packetize the signal content in any manner The received signal will be affected by such factors as noise edge jitter and interference but it is not purposefully manipulated or altered by the modules This gives the designer tremendous flexibility for protocol design and interface Despite this transparenc
29. ty to objects such as a user s hand body or metal objects will cause an antenna to detune For this reason the antenna shaft and tip should be positioned as far away from such objects as possible from a 1 4 or 1 2 wave straight whip mounted at a right angle to the ground plane In many cases this isn t desirable for practical or ergonomic reasons thus OPTIMUM an alternative antenna style such as a ein helical loop or patch may be utilized Figure 19 Ground Plane Orientation and the corresponding sacrifice in performance accepted NOT RECOMMENDED If an internal antenna is to be used keep it away from other metal components particularly large items like transformers batteries PCB tracks and ground planes In many cases the space around the antenna is as important as the antenna itself Objects in close proximity to the antenna can cause direct detuning while those farther away will alter the antenna s symmetry In many antenna designs particularly 1 4 wave TEATICALNa GROUNDED whips the ground plane acts as a counterpoise ANTENNA MARCONI forming in essence a 1 2 wave dipole For this reason adequate ground plane area is essential The ground plane can be a metal case or ground fill areas on a circuit board Ideally it should have a surface area gt the overall length of the 1 4 wave GROUND radiating element This is often not practical due to VRT Pore size and configuration constraints In
30. y eeeeeoeeoeeoeeoeeoeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eee 8 Specialty Styles Linx offers a wide variety of specialized antenna styles Many of these styles utilize helical elements to reduce the A Li overall antenna size while maintaining reasonable oio performance A helical antenna s bandwidth is often quite narrow and the antenna can detune in proximity to other ou objects so care must be exercised in layout and placement eeeoeeeeeeoeoeoeoeoeoeeeneeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee Loop Style A loop or trace style antenna is normally printed directly on a product s PCB This makes it the most cost effective of antenna styles The element can be made self resonant or externally resonated with discrete components but its actual layout is usually product specific Despite the cost advantages loop style antennas are generally inefficient and useful only for short range applications They are also very sensitive to changes in layout and PCB dielectric which can cause consistency issues during production In addition printed styles are difficult to engineer requiring the use of expensive equipment including a network analyzer An improperly designed loop will have a high SWR at the desired frequency which can cause instability in the RF stage Linx offers low cost planar and chip antennas that mount directly to a product s PCB These tiny antennas do not require testing and provide excellent performance in light
31. y and ease of use it must be recognized that there are distinct differences between a wired and a wireless environment Issues such as interference and contention must be understood and allowed for in the design process To learn more about protocol considerations we suggest you read Linx Application Note AN 00160 Errors from interference or changing signal conditions can cause corruption of the data packet so it is generally wise to structure the data being sent into small packets This allows errors to be managed without affecting large amounts of data A simple checksum or CRC could be used for basic error detection Once an error is detected the protocol designer may wish to simply discard the corrupt data or implement a more sophisticated scheme to correct it INTERFERENCE CONSIDERATIONS The RF spectrum is crowded and the potential for conflict with other unwanted sources of RF is very real While all RF products are at risk from interference its effects can be minimized by better understanding its characteristics Interference may come from internal or external sources The first step is to eliminate interference from noise sources on the board This means paying careful attention to layout grounding filtering and bypassing in order to eliminate all radiated and conducted interference paths For many products this is straightforward however products containing components such as switching power supplies motors crystals and othe
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