# Wireless Home Assistive System for Severely Disabled People
## 2 Materials and Methods
### The Assistive Input Accessories  
In order to help the severely disabled person control the MCT easily, we developed many kinds of assistive input accessories for them to choose, which are shown in Figure 2. When using an input digital switch, the time duration of press-and-hold is adopted to distinguish the long or short tonesof Morse code. In Figure 2, the assistive input accessories can be divided into three types, consisting of mechanical, sensing, and bio-signal (e.g., eye movement). The choice of input accessories is in accordance with the physical disability condition of each user. All three types of assistive input accessories mentioned above can output the similar digital outputs (different time duration of high/low level voltages) to represent the long/short tones and long/short silences of Morse codes to MCT. Any type of digital switches can be accepted as an assistive input accessory in WHAS if it can output similar digital output.  
The mechanical switches are shown in Figure 2a-d. The mechanical switch is mainly based on a push-button switch and a micro switch, which is not necessary to additionally provide a power to drive the switch. The mechanical switch is connected to a 3.5 mm mono male connector. When the switch is clicked, it will output a low voltage level; otherwise, it will output a high voltage level. To quickly input the Morse code to the MCT, a long-short tones switch (as shown in Figure 2d) is designed to input the long or short tones by using two buttons respectively.  
The sensing switches are shown in Figure 2e,f. An operational amplifier (OPA) comparator follows a photo sensor to provide a binary output. The OPA reference voltage value decides the reflection distance of the infrared light detected by the photo sensor. In order to avoid being triggered by unstable infrared reflection signals multiple times, we designed a Schmitt trigger circuit with feedback, whose reference voltage increases the stability of the special infrared switch. At the same time, two types of switches were designed according to different users' requests: one is the positive edge trigger (0\(\rightarrow\)1) switch, and the other is the negative edge trigger (1\(\rightarrow\)0) switch. In addition, a 555 oscillator integrated circuit (IC) is utilized to generate sound feedbacks by an external speaker module to check and confirm the Morse codes inputted when the user inputs Morse codes (short tones  
Figure 1: The architecture of the wireless home assistive system (WHAS).  
Figure 2: The kinds of input accessory. EOG: electrooculography.  
and long tones). The surface mount device type resistors, capacitors, and ICs were combined with a TCRT5000 infrared reflection sensor to reduce the size (4.8 cm \(\times\) 2.7 cm) and costs. The special IR switch is shown in Figure 2e.  
The electrooculography (EOG) assistive input switch shown in Figure 2g is a bio-signal switch. EOG is one of the common effective ways to measure eye movement. The range of EOG voltage is about 50 to 3500 \(\mu\)V, the frequency range is about DC 100 Hz, and the range of eye movement angle is about \(\pm\)30 degrees, which is proportional to the EOG voltage, so we can identify the direction and angle of the eyeball according to the eye movements. The EOG measurement circuit detects and amplified the differential signal of the eye movement by the INA128 instrumentation amplifier with the magnification 251; then, the second-order 1.6-10 Hz infinite impulse response band pass filter is designed for noise cancellation, which is finally followed by an inverse amplifier with 100 times amplification. After the EOG analog signal measurement, the single Schmitt-trigger inverter (SN74 LVC1G14) is utilized to complete analog/digital (A/D) conversion and become an EOG digital switch. Therefore, the user can use the EOG digital switch connected with MCT as a keyboard or mouse to input Morse codes by controlling the user's eye movement alone.