The following figure shows the external circuit alarm systems ranging peripheral circuit diagram, the system including power, reset, crystal oscillator, temperature, alarms, serial and digital display circuit.
PIC16F877A clock frequency can be used for 4MHz ~ 20MHz, the calculation basis to ensure the accuracy of the system, using 8MHz crystal, it is easy to set the number of transmit ultrasonic, ultrasonic center frequency is maintained at 40KHz. DS18B20 chip can be used for corrected speed of sound, to make the results more accurate. The system uses a buzzer alarm. Serial circuit can be achieved and PC communications. In order to facilitate the observation, the use of digital display distance measurement, PIC microcontroller RD0 ~ RD7 control seven segment digital tube election, RC1 ~ RC3 control bits selected to display dynamic scanning distance.
Figure ultrasonic ranging alarm system peripheral circuit
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