The transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy and transmits it to the left surface. Then, a set of precision reflection stripes under the glass plate reflects the sound wave energy into an upward uniform surface, and the sound wave energy passes through The surface of the screen body is then reflected by the upper reflection stripes to form a right line and propagates to the X-axis receiving transducer. The receiving transducer converts the returned surface acoustic wave energy into an electrical signal.
When the transmitting transducer emits a narrow pulse, the sound wave energy arrives at the receiving transducer through different ways, the earliest arrival on the far right, the latest arrival on the left, the sound energy of the early arrival and the late arrival are superimposed into one The wider waveform signal, it is not difficult to see that the received signal gathers all the sound wave energy returning through different paths in the X axis direction, and the distance they travel on the Y axis is the same, but on the X axis, the farthest ratio The nearest one has walked twice the maximum distance along the X axis. Therefore, the time axis of this waveform signal reflects the position of each original waveform before being superimposed, that is, the X axis coordinate.
Transmitted signal and received signal waveform When there is no touch, the received signal waveform is exactly the same as the reference waveform. When a finger or other object capable of absorbing or blocking sound wave energy touches the screen, the sound wave energy of the X-axis passing upward through the finger part is partially absorbed, reflecting that there is an attenuation gap on the received waveform, that is, the waveform at a certain moment.
The received waveform attenuates the signal corresponding to the signal blocked by the finger, and calculates the position of the notch to get the touch coordinates. The controller analyzes the attenuation of the received signal and determines the X coordinate from the position of the notch. After that, the Y-axis of the touch point is determined by the same process on the Y-axis. In addition to the X and Y coordinates that the general touch screen can respond to, the surface acoustic wave touch screen also responds to the third axis Z axis coordinate, that is, it can sense the magnitude of the user's touch pressure. The principle is calculated from the attenuation at the attenuation of the received signal.
Once the three axes are determined, the controller transmits them to the host.
