# Design and Implementation of a Semantic Information Expression Device Based on Vibrotactile Coding
## 2 Hardware Design
### Vibration Coding Design and Experimentation
#### 2.2.1 Vibration Intensity Perception Test Experiment  
The purpose of this perceptual experiment was to select a vibration intensity that would be strongly felt by the subject without discomfort. Before starting this experiment, a pre-test was conducted to find a suitable range of vibration intensity for the experiment.  
In the pre-test, it was found that when the duty cycle was 0.2, the vibration was just able to be perceived, and when the duty cycle was 0.7, the motor was obviously hot and accompanied by numbness, so the vibration intensity range selected for the experiment was 0.2-0.6.  
Then, in the formal test, the duty cycle interval can be set to 0.1, so there were 0.2, 0.3, 0.4, 0.5, 0.6 a total of five vibration intensities for the test. A total of 10 school students (five males and five females) were recruited, all of whom were right-handed and did not have any problems with tactile perception, and none of the subjects performed similar experiments prior to the start of the experiment.  
In order to prevent the vibration motor and the human body contact when the subject's force is not uniform, which results in biased experimental results, before the test, the vibration motor was taped to the fingers of the test subject, as shown in Figure 3, so that the vibration motor was in contact with the skin but did not produce extrusion. This was performed ensure that the vibration was clearly perceived by the subject and to avoid limiting the vibration amplitude of the motor.  
Since vibration produces a numbing sensation, this experiment was divided into two parts: one was the vibration sensation test and the other was the numbing sensation test. Both use the rating method, a total of seven levels, from zero to six indicating that the  
Figure 3: Diagram of a vibration motor tied to a finger.  
Figure 2: Framework diagram for the design of the system program. It is divided into the following steps: 1. Braille information is coded into the device. 2. The user learns the Braille and the device. 3. Testing the recognition accuracy. 4. The user interprets the Braille information.  
vibration or numbness was gradually strong. To ensure the accuracy of the experimental results in the vibration sensation and numbness test, the vibration intensity of the first sequential enhancement of the experiment was measured. Then, the vibration intensity was weakened sequentially. Finally, a random vibration intensity was assigned. Subjects perceived the vibration and numbness for rating and recording. Each vibration intensity was rated three times in the experiment, and a total of 30 levels were recorded for 10 subjects; then, the mean value of the levels recorded for each vibration intensity was calculated.  
The experimental results are shown in Figure 4. The condition required for suitable vibration intensity is that the vibration sensation is strong, but the numbness should not be strong. It is a matter of finding the value with the largest difference between the two. The difference between the vibration sensation and the numbness was calculated as 1.3, 1.8, 1.1, 1.3, 0.9, and the larger differences were 1.3 and 1.8, which corresponded to the vibration intensities of 0.2, 0.3, and 0.5. However, the numbness of 3.8 was too high when the vibration intensity was 0.5, so this vibration intensity was discarded. The final vibration intensity chosen was 0.2 or 0.3.  
In addition, since the perception of vibration is also affected by the vibration duration and the vibration interval time, excessively long or excessively short vibration duration and vibration interval may make the subjects' ratings of vibration sensation inaccurate. After testing, the optimal vibration duration was chosen to be 350 ms and the vibration interval time to be 300 ms.