Design of hospital call intercom system based on MSP430 and DTMF technology

With the rapid development of science and technology, especially the continuous updating of Electronic information technology, the reform of medical and health services has gradually deepened, and the realization of modern medical care has become the future development trend of the hospital. The hospital call intercom system is one of the important equipment to improve the hospital’s nursing level. First, its basic function is to make the nursing object communicate with the medical staff through a convenient way.

With the rapid development of science and technology, especially the continuous updating of electronic information technology, the reform of medical and health services has gradually deepened, and the realization of modern medical care has become the future development trend of the hospital. The hospital call intercom system is one of the important equipment to improve the hospital’s nursing level. First, its basic function is to make the nursing object communicate with the medical staff through a convenient way. The 16-bit MSP430 microcontroller has a high level of integration and rich on-chip resources. The main outstanding feature is low power consumption, which can achieve long-term stable work. After being applied to this system, the performance is well optimized, which can improve the medical staff. Improve work efficiency and reduce their labor intensity, patients can also receive timely care and medical treatment, which can significantly improve the hospital’s service level and medical quality.

1 Introduction of DTMF call intercom system

1.1 Introduction of DTMF Technology

DTMF (Dual Tone MulTI Frequency), that is, dual tone multi-frequency, is composed of a high frequency signal and a low frequency signal, which represent a number or character respectively. Dual-tone multi-frequency signaling is a combination of two specific single tones to represent numbers or functions. There are 4 kinds of high and low frequency signals, respectively forming high frequency group and low frequency group. The combination of 8 to 1 is used to form DTMF signal, so there are 16 kinds of configurations, which can represent 0-9, A-D, * on the dial pad respectively. , # and other 16 characters, according to the signal frequency and character corresponding to a table (as shown in Table 1). Due to its good anti-noise properties, it is widely used in dial-up transmission in communication systems.

Design of hospital call intercom system based on MSP430 and DTMF technology

1.2 The working principle of the call intercom system

The host and extension of the system are controlled by the single-chip microcomputer. Since there is only one host in the whole call system, it is the core module of the system. It can be connected with the extension through the external bus to realize the function of call intercom. The host can receive the call of the extension at any time, and the digital Display screen and the patient information list display table can display the corresponding information synchronously and accurately. There are primary, secondary and tertiary nursing levels. When there are multiple call signals, Displayed cyclically according to the level of care and the order of dialing.

2 Overall design of the system

The system can be divided into three parts in space, namely the duty room of medical staff, the ward and the corridor (as shown in Figure 1). The host computer, telephone and patient information list display table are installed in the duty room of the medical staff, the extension is installed in each bed of each ward, and the digital display screen is installed in the corridor. When the host is in standby, the digital display on the corridor displays information such as date and time. When a patient uses an extension to call the host, the host in the medical staff duty room will send a bell signal, and the patient information list and the number on the corridor will be displayed at the same time. The display screen will display the information of the corresponding patient. After the call is connected, the medical staff will know the situation of the patient so as to prepare the corresponding medical measures.

Design of hospital call intercom system based on MSP430 and DTMF technology

3 Main hardware circuit design of the system

3.1 The hardware design of the host

The system is mainly composed of single chip microcomputer, DTMF signal sending circuit, DTMF signal receiving circuit, DTMF signal decoding circuit, ringing detection circuit, on-hook detection circuit and other parts, as shown in Figure 2.

Design of hospital call intercom system based on MSP430 and DTMF technology

The design of the host adopts the MSP430F149 microcontroller as the core control module, which not only controls the sending and receiving of the host and extension numbers, but also controls the connection between the host and the extension, the on-off of the ringing signal, and the display. When the system is in normal working state, when the host calls an extension, through the corresponding signal detection, after the host phone goes off-hook, it dials the extension number, and the DTMF signal is decoded and sent to the corresponding extension. After the extension phone goes off-hook, the host You can make a call with the extension, and hang up after the call. When the medical staff needs to broadcast, start the group call function, the host broadcasts to all extensions, and ends after hanging up. When an extension calls the host, the host receives the signal and encodes it, and sends it to the single-chip microcomputer through the decoding circuit. After the CPU reads the information, the display circuit displays the number and calling time of the corresponding extension. After the host phone goes off-hook, it rings. After the signal is cleared, the extension and the host can communicate.

3.2 DTMF signal transceiver circuit

The DTMF signal transceiver circuit of this system adopts MT8880, which has high integration and low power consumption, and can be used to send and receive DTMF signals. Use Protues to design the transceiver circuit, as shown in Figure 3, the A port is connected to the bus, and the B port is the DTMF signal transceiver. The MT8880 uses a standard single-chip control interface, and the single-chip computer can accurately complete the receiving and sending functions.

Design of hospital call intercom system based on MSP430 and DTMF technology

When in the sending state, the 4-bit binary code on the data bus is latched into the sending data register, and the frequency of the transmitted signal is generated by frequency division of the crystal oscillator frequency, and 8 different frequency signals are separated from the reference frequency. The combination method selects a group of high and low frequencies to synthesize a DTMF signal. When in the receiving state, after the DFMF signal is input, it is separated into a group of high and low frequency signals, and after detection, it is translated into the corresponding 4-bit binary code, and then latched in the receiving data latch.

3.3 Signal decoding circuit

The host phone calls the extension using the dialing principle of the telephone. The host phone dials the extension number, and the DTMF signal sent out obtains the address signal of the corresponding extension through the decoding circuit. The system uses MT8888 as the decoder chip, which has powerful functions, simple circuit, low power consumption, high stability and strong anti-interference ability. The chip has few external electronic components and is easy to connect with the MCU interface. The decoding circuit is designed by Protues. As shown in Figure 4, the P1.1 end of the single-chip microcomputer is connected to the RD end of the MT8888 as the read strobe function, and the P1.2 end is used as the write strobe function to connect to the WR end of the MT8888. When there is a DTMF signal input in the middle circuit, it is latched into the output register, so that the IRQ terminal outputs a high level. After the CPU queries the signal, it controls the MT8888 to make the RD and CS terminals valid, and at the same time, the 4 representing the dialed number is set. Bit binary code is sent to the CPU for processing.

Design of hospital call intercom system based on MSP430 and DTMF technology

3.4 Ringing Detection Circuit

When a user calls the machine, the telephone exchange sends a ringing current signal, so it can be judged whether there is a calling signal by detecting whether there is a ringing current signal. The ringing detection circuit of this system is composed of 4 diodes D1~D4, 2 Zener diodes D5, D6, 1 resistor R and 1 capacitor C. The IN1 and IN2 terminals are the input terminals of the ringing current signal, and the OUT1 terminal and the The OUT2 terminal is the ringing detection output terminal. When there is no ringing signal input, the Zener tube D5 cannot be turned on, and the output voltage of the ringing detection circuit is approximately 0V. At this time, the detection result is that there is no ringing signal; when there is a ringing signal input, due to the diode The circuit composed of D1~D4 has the function of rectification, the signal is converted into pulsating direct current, the capacitor C is charged through the resistor R, and the output terminal of the ringing detection circuit generates a voltage. At this time, the detection result is a ringing signal. The function of the Zener diode D6 in the circuit is to limit the amplitude of the ringing signal to prevent the input voltage from being overheated and burning out the circuit components.

3.5 Off-hook detection circuit

The on-hook detection circuit is used to detect the off-hook state and input it into the microcontroller control system. The detection signal of picking up and hanging up is input to the P1.3 pin of the microcontroller, the magnet is installed on the microphone, and the reed switch is installed inside the telephone. The closing and disconnection of the reed switch can realize the closing and disconnection of the microphone and the telephone. . When the phone is off-hook, the microphone and the phone are separated. Because of the loss of the attraction of the magnet, the shrapnel of the reed switch is disconnected, and the P1.3 pin inputs a high level; when the phone is on-hook, the microphone and the phone are closed. The attraction effect, P1.3 pin input low level, so you can detect off-hook by querying the level state of P1.3 pin.

4 System software design

According to the need, design the calling work flow chart of the host (as shown in Figure 5). When the host is in an idle state, that is, when there is no call or conversation, the digital display on the corridor will display the real-time date and time and other information. If not, execute the key query to determine whether to dial the call; when the host and the extension are talking, after the two parties are connected, the digital display will display the relevant information of the patient, such as ward number, bed number, etc.

Design of hospital call intercom system based on MSP430 and DTMF technology

5 Experimental simulation analysis

In order to verify the reliability of the DTMF signal, MATLAB is used for simulation experiments. A set of DTMF signal frequency groups needs to be set. In this experiment, the DTMF signal of button “0” is selected, and the corresponding frequency groups are 1 366 Hz and 941 Hz. After importing into MATLAB, the time domain waveform of the signal can be obtained (as shown in Figure 6). ), and then select other frequency groups to conduct simulation experiments and obtain similar results. This experiment shows that a group of high and low frequencies can be effectively combined into a DTMF signal, and can be accurately identified and processed. Due to the high efficiency of DTMF dialing rate, it avoids the defects caused by the traditional dialing method and ensures the accuracy of the signal. ground transmission, the feasibility of the system can be affirmed.

Design of hospital call intercom system based on MSP430 and DTMF technology

6 Conclusion

The system structure design is relatively simple, with MSP430F149 microcontroller as the control core, using DTMF signal communication technology, can effectively reduce the cost of the system, improve its reliability and anti-interference ability. The system is easy to assemble and maintain, easy to operate, and convenient for medical staff and patients to use. The patient can directly communicate with the medical staff in the duty room, which greatly improves the doctor-patient relationship. Received attentive care and trust in the hospital also increased. The key point of the system studied in this paper is to design an effective and convenient call intercom system, which basically achieves the design goal, but the technology is always developing, and the technology will be gradually updated. In the future, the function of the hospital call intercom system will continue to be Complete.

The Links:   2MBI300LB-060 KCS057QV1BR-G21

Author: Yoyokuo