An ISD4004 voice chip application circuit based on single-chip microcomputer control

1 Introduction
The ISD4004 voice chip is a new product recently launched by the American ISD company. As the pin description and internal circuit of the voice chip can be easily found in the chip data provided by ISD, I will not describe it in detail in this article. I will only briefly introduce its characteristics.
Compared with ordinary recording/playback chips, ISD4004 has the following characteristics: First, there is no limit on the length of the recorded sound segment, and the sound recording does not require A/D conversion and compression. Secondly, the fast flash memory is used as a storage medium, which can save data for up to 100 years without power supply and record more than 10,000 times. In addition, ISD4004 has the advantage of long recording time (up to 16 minutes, and this article uses the 8-minute ISD4004 voice chip). Finally, the development and application of ISD4004 has the advantage of simple peripheral circuits, which can be experienced from its actual application in the voice station announcer introduced in this article.

2 Hardware Circuit Design
Most of the voice station announcers currently on the market do not use the ISD4004 series chips. This is certainly because ISD4004 was launched not long ago and its price is relatively high. However, with the increase in the application of ISD4004 and the decline in price, coupled with the advantages of the ISD4004 series chips themselves, such as multiple repeated recording and playback, built-in memory, and simple use. It is believed that it is completely feasible to use the ISD4004 series voice chips in the voice station announcer. The author designed the hardware circuit of the device and conducted on-board debugging, and achieved relatively satisfactory results.
The voice station announcer discussed in this article mainly refers to the playback circuit installed on the car, and does not include the recording circuit. In actual applications, the recording circuit completes the recording of the station announcement content and stores it in the voice chip. This article mainly introduces the typical application of ISD4004 in combination with the use of ISD4004 in the playback circuit.

2.1 Hardware Circuit Diagram
The main circuit of the station announcer discussed in this article is mainly composed of the single-chip microcomputer 89C52 and ISD4004. The hardware circuit connection of the system is shown in Figure 1:

Figure 1

This system can be mainly divided into three parts. The single-chip control part, the playback part and the display part. The display circuit in this article adopts the static display of two 7-segment digital tubes controlled by P3.0 and P3.1, which will not be introduced in detail here. The control part is mainly composed of the single-chip microcomputer 89C52, which contains the necessary peripheral circuits such as key circuit, reset circuit and watchdog circuit. The playback part is mainly composed of ISD4004, which contains the matching transformer circuit, power amplifier circuit, etc.
It can be seen from the figure that there are few connections between 89C52 and ISD4004. The P1.0-P1.3 pins of the single-chip microcomputer are connected to the buttons to control whether the station announcer plays and the playback content during the working process. P1.6 is connected to the chip select pin /SS of ISD4004 to control whether ISD4004 is selected or not. P1.7 is connected to the serial input pin MOSI of ISD4004, and the playback address is read from this pin. P3.0 and P3.1 control the peripheral display circuit, and display the current station number during the station announcer operation. P3.2 and P3.3 are connected to the serial clock pin SCLK and interrupt pin /INT of ISD4004 respectively. The ISD4004 chip also needs to connect the audio signal output pin AUDOUT, which is connected to the speaker through a filter capacitor. AMCAP is the automatic mute terminal, which is grounded through a capacitor when in use. In addition, since the operating voltage of ISD4004 is 3 volts, and the power supply voltage required by the microcontroller is 5 volts, a transformer circuit is required to obtain a 3 volt voltage for ISD4004. [page]

3 Software Design
3.1 Program Flowchart
As shown in Figure 2:

Figure 2

3.2 Program working idea
After the circuit is powered on, the program first completes the program initialization, then queries the button status and enters the system standby state. If a button is pressed, it will turn to execute the working program pointed to by the button. The buttons include the play button, stop button, plus one, minus one button and special language button. In the standby state, if the play button is pressed for the first time, the program will first determine whether it is going or returning (the bus route is generally both going and returning), and light up the corresponding indicator light. Automatically read out the playback content of the first station, and the station number is displayed as 1. If it is not the first time, the program first determines the current station number, and uses the station number as the basis to obtain the first address of the playback content of the station. Call the playback subroutine, read the first address of the playback content of this station obtained previously, and start playing. After each sentence is played, the interrupt pin (pin 25) of ISD4004 will automatically send a low-level signal. In the hardware design, this pin is connected to P3.3 of the microcontroller. Therefore, an interruption will be caused. In the interrupt subroutine, there will be a counter to record the number of interruptions, so as to determine when a station ends, and the station number will be increased by one and refreshed. After pressing the plus key, the program will switch to the next station, and the minus key will switch to the previous station. The corresponding station number display will also be refreshed. After the special language key is pressed, the program will switch to execute the special language playback (such as "Please pay attention to the turn"). Pressing the stop key will terminate the current playback state.
3.3 Partial working subroutines
In order to facilitate readers' understanding of the application of ISD4004, this article gives some operating procedures.
This part of the program mainly completes the playback operation, sends the address of the obtained playback content to ISD4004, and completes the playback. The following is the playback part of the program. Playback subroutine:
PLAY:
ACALL POWERUP ;Electronic program
ACALL DELAY25 ;Delay subroutine, at least 25ms delay
CLR P1.6 ;Select ISD4004
MOV PLAY2,#11100000B ;Store SETPLAY command
MOV A,PLAY0 ;Send the lower 8 bits of the playback address
ACALL SEND ;Call the address sending subroutine
MOV A,PLAY1 ;Send the higher 8 bits of the playback address
ACALL SEND
MOV A,PLAY2 ;Send SETPLAY command
ACALL SEND
SETB P1.6
CLR P1.6
MOV PLAYING,#11110000B ;Send the playback instruction
MOV A,PLAYING
ACALL SEND
SETB P1.6
RET
POWERUP: ;Send the power-on instruction subroutine
MOV POWING,#00100000B ;Send the power-on signal of the voice chip
MOV A,POWUPING
CLR P1.6
ACALL SEND
SETB P1.6
RET
SEND: ;Subroutine to send instructions, addresses, etc. to ISD4004
CLR MOSI
CLR P3.2
MOV R1,#8
OUTBIT1:
CLR P3.2 ;Clock falls
RRC A
MOV MOSI,C ;Output 1 bit
NOP
NOP
NOP
SETB P3.2 ;Clock rises to
NOP
NOP
NOP
DJNZ R1,OUTBIT1
RET
3.4 Some issues to note when programming and debugging
In the playback program, programming must be strictly in accordance with the requirements of ISD4004. First, send the power-on instruction, then wait for a 25 millisecond delay, then send the 16-bit playback start address, and finally send the 8-bit start playback instruction.
In the debugging process of the playback circuit, first measure whether the operating voltage of ISD4004 is 3 volts. If it is, enter the lower level debugging. Then check whether the playback address can be sent in. You can measure the voltage of the AUDOUT pin. If it is 1.2V, it means that the playback address can be read in. Then measure whether the sound can be played. You can measure the voltage of the AUDOUT pin. If it is 1.2V, it means that the ISD4004 chip is working properly and should be able to play. If you still can't hear the sound, you can debug the subsequent playback circuit to see if there is a problem with the subsequent circuit.

4 Conclusion
This article introduces a practical application of ISD4004 voice chip in voice station announcer, so that readers can be familiar with the basic application of 1SD4004. At the same time, the station announcer circuit introduced in this article has been debugged by on-board experiments and can work reliably and stably.

References
1 Li Hua, "MCS-51 Series Single-Chip Microcomputer Practical Interface Technology", Beijing University of Aeronautics and Astronautics Press, 1993
2 Xue Junyi, Zhang Yanbin, "MCS-51/96 Series Single-Chip Microcomputer and Its Application", Xi'an Jiaotong University Press, 1997, 2nd edition
3 Wang Zhenhong, Li Yang, Hao Chengxiang, "The Working Principle of ISD4004 Voice Chip and Its Application in Intelligent Control Systems", Electronic Devices, Vol. 25, No. 1, March 2002