Ultrasonic transmitter and receiver split ruler (GPS/BDS chip PPS signal is used as time synchronization, the synchronization error is about ten microseconds)
This is a self-made project that I have published on Weibo, Bilibili (https://www.bilibili.com/video/BV1g54y187NT) and blog.csdn.net (https://blog.csdn.net/garfield0424/article/details/114960031).
*** Welcome to give me some comments on this production!! ***
Ultrasonic transmitter and receiver split ruler (GPS/BDS chip PPS signal is used as time synchronization, the synchronization error is about ten microseconds)
The PPS output of the Beidou chip is used to provide the time synchronization function of the ultrasonic ruler transmitter and receiver. Generally, ultrasonic rulers rely on the ultrasonic wave reflected from the target object to obtain the time the ultrasonic wave travels in the air, and then multiply it by the speed of the ultrasonic wave in the air to get the distance, and then divide it by 2 to know how far the object is from the ultrasonic ruler instrument. However, the object must be able to reflect enough ultrasonic energy back to the instrument, exceeding the minimum energy measurement requirement of the ultrasonic receiver to measure it. The PPS signal of the Beidou chip is 1Hz. At the beginning of each second, a square wave signal with a time shorter than one second is generated by the PPS signal. The rise time position of this square wave signal received by all devices and instruments will be extremely accurate time synchronization. The PPS signal output of the Beidou chip that can be purchased generally has a rise time position accuracy of less than 100ns in the square wave signal received by different devices and instruments. 1ns (1 nanosecond) = 0.000000001 seconds. My ultrasonic ruler cannot reach this level of accuracy, mainly because the clock time signals of the two microprocessors are not synchronized, and the frequency of the clock crystal is not necessarily accurate. There are also some Beidou chip models produced specifically for time synchronization, and the PPS time synchronization accuracy of the chip output can be far better than 100ns.
The general ultrasonic distance measurement is not difficult. As long as you buy a transceiver component, you can calculate the distance by the time required for the component to emit and receive the ultrasonic wave, plus the speed of the ultrasonic wave in the air. In the above project, only two normal ultrasonic transceivers are needed. The Beidou chip PPS output is used as time synchronization to make two identical transceivers perform normal distance measurement at the same time. The two components will send out ultrasonic distance measurement signals at the same time, but they will first receive the ultrasonic signal emitted by the other party, rather than their own ultrasonic signal reflected back. Therefore, both parties will measure the distance between them, rather than the distance twice the distance after the ultrasonic wave is reflected back to themselves. Generally, the Beidou satellite signal at home is very weak, so you must buy a Beidou satellite signal amplifier. The receiving antenna must be placed outdoors to receive and amplify the Beidou satellite signal, and then use the output antenna of the amplifier to send the Beidou satellite signal indoors. In addition, the Beidou chip PPS output must be the output after successful positioning, which will be a real real-time Beidou PPS signal. When setting the Beidou chip parameters, you must select FIXED in the positioning parameter option. Otherwise, the Beidou chip may output some estimated PPS signals at some times because it cannot receive real-time Beidou satellite signals. At this time, the time error of the PPS signal output by the Beidou chip when received by different devices and instruments will be far more than 100ns.
The system operation principle diagram is as follows. T transmit (transmitter-receiver integrated ultrasonic component [transmitter role] ranging start time) = T receiver timer (transmitter-receiver integrated ultrasonic component [receiver role] ranging start time)
The distance calculation results of the two ultrasonic transceiver components of my ultrasonic ruler can be confirmed to be the distance calculation results obtained after receiving the ultrasonic signal sent by the other party. Because there is a GPS/BDS PPS signal and there is no signal, the two components will obtain different distance calculation results. If a solid plate is placed between the two transceiver components during normal operation, and then moved left and right, the distance calculation results on both sides and the measured distance that should be obtained after the ultrasonic wave is reflected from the solid plate and returns to each component are completely consistent. In this case, the sum of the distance values obtained by the two components divided by 2 will be approximately equal to the normal distance display value without a solid plate placed in the middle.
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