Based on the identification of DTMF and voice automatic playing system (1)

1 Introduction

Due to the radio use full transparent transmission mode, as long as the band the same, you can receive the same band speech signal sent over, so you cannot accurately identify signal is useful.

With voice encryption for radios you can avoid this situation, but in some areas require confidentiality high or places, such as the military sphere, interception once cracked we keying signals, issued a misleading speech signal, we are unable to discern that may cause certain losses. So, here is a microprocessor based on C8051F to DTMF encoding of the how to identify the identity of the radio system. The system is simple to use, without changing the radio and on the basis of the original features, and expansion port connection radio station, that enables the identification of the station's identity. Even if the other crack a voice signal, also available through the address encoding to distinguish the identity of the radio. The system in place for confidentiality requirements have a certain application.

2. system composition and working principle

Figure 1 to identify the identity of the radio system map.

SCM selection C8051F020, DTMF unit selection MT8880 dual tone multiple frequency divider, voice storage playback module using ISD4004, display unit, storage unit, a keyboard.

Radio stations are generally reserved for extended interface: audio input, audio output, PTT emission control, power supply, ground.

The system passes these interfaces are connected with radio stations, as shown in Figure 2.

The system works: as the transmitter is station press the PTT key, FTT from high to low level, and the signal into single-chip, microcontroller interrupt program native code through data interfaces to MT8880, after being pulled into the station MT8880 modulation of audio input interface, along with the voice signal.

As the receiver is divided into a variety of circumstances, as shown in Figure 3.

Receives a voice signal, the judgement whether DTMF signal input.

If so, MT8880 decoding, the decoded data transfer to another judge C805117020 C8051F020, this address is predetermined by the radio address code. If so, the code shown on the LCD; otherwise, it displays the ERROR; if no DTMF signals and only the voice signal, the signal signal linked by this website, the operator through the play keys back matter prerecorded some confused speech signal each other.

3 system hardware design

The entire system based on the functionality can be divided into DTMF series/decoding and playback of voice storage.

And control by the master unit. Due to the system by radio battery, so choose a low-power devices. Here the master unit adopts C8051F020. It is a fully integrated, mixed-signal system-on-chip (SoC), and 8051-compatible high-speed CIP-51 kernel, and are fully compatible with MCS-51 instruction set. C8051F020 clock frequency up to 25 MHz, contains 64 KB on-chip Flash program memory, 4 352 B RAM, 8 I/O ports, I/O line 64 root.

3.1 DTMF series/decoding

DTMF encoder／decoder MT8880 selection.

MT8880C is a call-handling filter monolithic DTMF signal transceiver. This device uses low-power, high stability of ISO-CMOS technology, built-in 1 internal with variable gain amplifier for high-performance receiver, 1 x transmitter with pulse counters, and one accessible MT8880 internal registers of standard microprocessor interface. Its internal registers including 1 status register, 2 data registers and 2 control registers, the circuit shown in Figure 4.

[1] [2]