Wireless unit call system design (1)

1 Introduction

Currently, the hospital wards call system used for wired calls system, there are complex wiring, cabling costs are relatively high, easy-to-fail, maintenance inconvenient, line against unsightly defects.

This article describes wireless calling system without these shortcomings, easy installation, low cost, easy to use.

2 system hardware design

This system utilizes MCS serial transmission function, will the serial output signal to the transmitter, when the signal is high level high-frequency transmitter, 433 MHz, and fired amplitude, high frequency signal, when the signal is low-frequency transmitter usually stop working, so high-frequency transmitter completely controlled by microcontroller serial digital signal output, high frequency circuit complete amplitude shift keying (ASK modulation).

Super carrier receive Board receive high frequency signal, the signal decoding, sound and light alarm, dynamic displays, and other functions from the microprocessor.

2.1 system host design

This system of the host to AT89C51 as core, electric circuit as shown in Figure 1, power supply circuit and part from the machine circuit power (see Figure 2).

Host circuits including HF transmitter module, Super carrier receiver module, digital display driver module, keyboard, sound and light alarm, reset circuit, etc.

Standby, the digital display all zeros, sound and light alarm circuits are not working. When the patient press installed in the head of the press from the machine, installed in the nurses station hosts receive signal after 3 sound "di" beep, led light, led display call patient beds, and the call number, doctor or nurse under display beds, for the treatment and services. The host has the memory of the 9 groups recently call, and call number of beds.

There is a full-duplex AT89C51 asynchronous serial communication interface can be used as UATR (universal asynchronous receiver and transmitter), can also be used to synchronize the shift register.

During the system design, works for serial UATR 1. Microcontroller to a serial communication mode, serial port 1 is detected by the "l" to "0" jump start serial receive when began, and the MCU in non-serial communication window output to "1", so before the transmitter and receiver modules need to be combined with one gate to prevent emission circuit in the non-communication have been at the launching State, so as to satisfy simultaneously your microcontroller serial communication requirements to ensure that single-chip transceiver data correctly. Need to launch the data signal from the output of 11 pin AT89C51 by reversed phase high frequency to 433MHz after transmitting circuit to launch. The high-frequency transmitter using surface acoustic wave (SAW) resonator frequency stabilization, stable performance, do not need any debugging to work properly. Because of the high-frequency receiver circuit vulnerable to interference, it is difficult to debug, and sale of finished receiving module performance stability, low prices, so the system adopts the final receiver module, the module received signal fed RP AT89C51 after 10 pin is decoded.

2.2 system design from machine

From the machine adopts AT89C2051 as a core, mainly through serial communication, press scan, sound and light alarm function.

SCM Pl port is set to user, which can be freely modified data, users dial the code for any of the settings as needed for Pl estuary high or low level, a total of 256 setting means 256 beds number, as shown in Figure 2.

　　

Circuit is equipped with a call button that patients should call nursing desk, just press the key, the led is flashing.

The host receives the call after the issue of sound and light alarm reminder on-duty doctor or nurse, doctor or nurse if duty by host response keys from the machine receives a signal after sound and light alarm, the indicator light flashes 4 times, the buzzer emits 3 sound "di", which prompts the patient's doctor or nurse has received the call. From the machine's serial signal transmitting and receiving circuits and host are the same, no longer dwell.

3 software design

3.1 emission data format

SCM and receive modules, usually the user can customize the transport protocol, irrespective of the modulation, the messages code format is important, it will have a direct impact on the reliability of sending and receiving data.

Common information code format: preamble + synchronous code + data frames.

Preamble launch time should be greater than 10 ms, to avoid background noise, because the receiver module receives first data can easily be interference (i.e. the zero level of disturbance) and receive data errors.

So in launching synchronous code with some preamble to suppress zero levels of interference. Synchronous code is mainly used to distinguish between a preamble and data, there are certain characteristics that make the software through a certain algorithm to identify synchronization code, but do receive data preparation. Data frame that is the signal to be transferred.

This system is the use of single-chip serial communication, data sending 4 frames, the first frame to an 8-bit full-0, the second frame for 8-bit full 2 1 code, this is the preamble frame data, practice has shown good suppression of zero-level disturbance; the third frame is 8-bit synchronous code to different synchronous code constitute 256 different set of calling system; fourth frame 8 bits represent 256 different beds number.

After the software is later found received before 2 frames for 0 yards and l code to start receiving synchronization frame and data frames. The software determines the synchronization frame data call systems of synchronous code after decoding the data frame, display beds and calls, and to sound and light alarm.

3.2 host software design