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I. Preface
Yesterday I tested the effect of ultrasound on the crystal oscillator of the watch. Since ordinary ultrasonic emitters generally resonate at 40kHz, the following re-measurement of the 40kHz crystal oscillator is affected by ultrasound.
Second, the test circuit design
This time, I tested it with a G031 chip that I had just purchased a few days ago. It only has a low-frequency crystal oscillator circuit, and it can also output low-frequency signals. This makes it easy to perform frequency tests. The board is very simple. The low-frequency signal is routed through a port for easy oscilloscope measurements. Design a single-layer circuit board so that it fits into one-minute boarding.
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▲ Figure 1.2.1 Schematic diagram of test circuit
▲ Figure 1.2.2 The circuit board is obtained after testing the PCB for one minute. Let's take a weld test.
The circuit board is soldered, cleaned and tested. In particular, the G031 first pin logo is not easily recognized.
3. Replace the circuit
It was still inexperienced, until the final test found that the output of the G031 was not the frequency of the external crystal, but the internal 32kHz low-frequency signal. So I had to change to the F103 that I used two days ago. After re-making the plate for one minute, soldering the circuit, the original program is downloaded, and the square wave signal after the crystal oscillator is divided by 64 can be measured on the Tamper pin.
The microcontroller Tamper pin outputs a 625Hz square wave signal, which is a 40kHz divide-64 frequency. The DG1062 generates a peak-to-peak 10V sine wave at 40kHz applied to the ultrasonic transmitter. At this point, the emitter is not aligned with the crystals on the board. It can be seen that the square wave output of the microcontroller and the sine wave of the signal source are not locked in frequency. If the ultrasound waves are aimed at the crystals on the circuit board, there is an effect between the two signals. When the ultrasonic wave is closer to the crystal, the square wave of the microcontroller and the signal of the ultrasonic sensor are locked together. Adjust the frequency of the ultrasonic driving signal, and you can see that the phase between the square wave of the single-chip microcomputer and it will change again. Within a certain frequency error range, the ultrasonic wave and the microcontroller crystal signal will be locked. After experimentation, this lock signal frequency range is approximately 1.6Hz. That is, if the difference between the oscillation frequency of the crystal and the ultrasonic frequency is within 1.6Hz, the two will be completely synchronized.
※Summary※
In this paper, the phenomenon of ultrasonic frequency locking of a 40kHz crystal oscillator is tested. At 40 kHz, the emission efficiency of the ultrasonic sensor increases, as does the distance and frequency range of the influence on the crystal.