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RXM-900-HP3-PPS Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers |
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RXM-900-HP3-PPS Datasheet(HTML) 5 Page - List of Unclassifed Manufacturers |
5 / 13 page Page 9 Page 8 THE DATA OUTPUT The DATA line outputs recovered digital data. It is an open collector output with an internal 4.7k Ω pull-up. When an RF transmission is not present, or when the received signal strength is too low to ensure proper demodulation, the data output is squelched continuous high. This feature supports direct operation with UARTs, which require their input to be continuously high. An HP3 transmitter and receiver can be directly connected between two UARTs without the need for buffering or logical inversion. It should be noted that the squelch level is set just over the receiver’s internal noise threshold. Any external RF activity above that threshold will “break squelch” and produce hashing on the line. While the DATA line will be reliably squelched in low-noise environments, the designer should always plan for the potential of hashing. AUDIO OUTPUT The HP3 Series is optimized for the transmission of serial data; however, it can also be used very effectively to send a variety of analog signals, including audio. The ability of the HP3 to send combinations of audio and data opens new areas of opportunity for creative design. The analog output of the AUDIO line is valid from 50 Hz to 28 kHz, providing an AC signal of about 1V peak-to-peak. This is a high impedance output and not suitable for directly driving low-impedance loads, such as a speaker. In applications where a low impedance load is to be driven, a buffer circuit should always be used. For example, in the case of a speaker, a simple op-amp circuit such as the one shown below can be used to act as an impedance converter. The transmitter’s modulation voltage is critical, since it determines the carrier deviation and distortion. The transmitter input level should be adjusted to achieve the optimum results for your application in your circuit. Please refer to the transmitter data guide for full details. When used for audio, the analog output of the receiver should be filtered and buffered to obtain maximum sound quality. For voice, a 3-4kHz low-pass filter is often employed. For broader-range sources, such as music, a 12-17kHz cutoff may be more appropriate. In applications that require high-quality audio, a compandor may be used to further improve SNR. The HP3 is capable of providing audio quality comparable to a radio or intercom. For applications where true high fidelity audio is required, the HP3 will probably not be the best choice, and a device optimized for audio should be utilized. HP Analog Out 10k 6 2 3 + – 4 LM386 5 0.05uF 1uF 250uF 10 ohm VCC Figure 12: Audio Buffer Amplifier TIMING CONSIDERATIONS There are four major timing considerations to be aware of when designing with the HP3 Series receiver. These are shown in the table below. T1 is the maximum amount of time that can elapse without a data transition. Data must always be considered in both the analog and the digital domain. Because the data stream is asynchronous and no particular format is imposed, it is possible for the data to meet the receiver’s data rate requirement yet violate the analog frequency requirements. For example, if a 255 (0FF hex) were sent continuously, the receiver would view the data as a DC level. It would hold that level until a transition was required to meet the minimum frequency specification. If no transition occurred, data integrity could not be guaranteed. While no particular structure or balancing requirement is imposed, the designer must ensure that both analog and digital signals meet the transition specification. T2 is the worst-case time needed for a powered-up module to switch between channels after a valid channel selection. This time does not include external overhead for loading a desired channel in the serial channel-selection mode. T3 is the time to receiver readiness from the PDN line going high. Receiver readiness is determined by valid data on the DATA line. This assumes an incoming data stream and the presence of stable supply on VCC. T4 is the time to receiver readiness from the application of VCC. Receiver readiness is determined by valid data on the DATA line. This assumes an incoming data stream and the PDN line is high or open. RECEIVING DATA Once an RF link has been established, the challenge becomes how to effectively transfer data across it. While a properly designed RF link provides reliable data transfer under most conditions, there are still distinct differences from a wired link that must be addressed. Since the modules do not incorporate internal encoding or decoding, the user has tremendous flexibility in how data is handled. It is important to separate the types of transmissions that are technically possible from those that are legally allowed in the country of operation. Application Notes AN-00126, AN-00140 and Part 15, Section 249 of the FCC rules should be reviewed for details on acceptable transmission content in the U.S. If you want to transfer simple control or status signals (such as button presses) and your product does not have a microprocessor or you wish to avoid protocol development, consider using an encoder / decoder IC set. These chips are available from several manufacturers, including Linx. They take care of all encoding and decoding functions and provide a number of data lines to which switches can be directly connected. Address bits are usually provided for security and to allow the addressing of multiple receivers independently. These ICs are an excellent way to bring basic remote control products to market quickly and inexpensively. It is also a simple task to interface with inexpensive microprocessors or one of many IR, remote control, DTMF, or modem ICs. Parameter Description Max. T1 Time between DATA output transitions 20.0mS T2 Channel change time (time to valid data) 1.5mS T3 Receiver turn-on time via PDN 3.0mS T4 Receiver turn-on time via VCC 7.0mS |
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