Tag Archives: signal

Seg 7: Look for the wifi networks

(2) Look for the wifi networks

Figure 2-8 Look for the wifi network signal

After setting the relevant parameters by the above-mentioned step (1), we can find the wifi signal transmitted from wifi board according to the followings.

  1. After power on the wifi board for about 30 seconds, the three LED lights would be exhibited normally. That is, LED1 is lighting with red all the time, LED2 is light with green all along as well, and LED3 is blinking with green light. The relevant context can be referred as shown in Section 2.3. Then, clicking the network icon, you would find there are many wireless network signals, where there is a named as HI_LINK_XXXX wifi signal, which is the wanted wireless wifi network signal. Therefore, we can double click such wifi signal, then it is needed to input password 12345678, which is the default password. If it is the first connection, it needs us to input the password, but thereafter, we may not input the password. Note that, the later 4 letters “XXXX” in the wifi signal name HI-LINK_XXXX is denoted by the different names, since their names may be different according to the different wifi devices. For example, in our such example, the name of wifi signal is HI-LINK_0021, which is also the same as the name encountered in the mobile phone. After double clicking the HI-LINK_0021 wifi signal and input the password, we can make the computer connect to the wifi module on the Arduino shield board, as shown in Figure 2-8.
  2. According to 1), we can connect the wifi network HI-LINK_0021 transmitted from wifi module. Then, return to the network-serial assistant shown in Figure 2-6, click the “Open” button on the left serial setting, and click the “Connect” on the right wifi setting, which are denoted by opening the serial port COM6 and connecting wifi network HI-LINK_0021, as shown in Figure 2-9 with red label. Note that, if the serial port doesn’t open, or the wifi network doesn’t be connected, the buttons “Open” and “Connect” would not work normally, and thus we cannot change the states of buttons “Open” and “Connect”. In other word, “Open” cannot be changed into “close”, and “Connect” cannot be changed into “disconnect”.

Figure 2-9 open the serial port and connect wifi network

  1. After connecting the serial port and wifi networks by Figure 2-10, we can transmit and receive data between serial port and wifi module, as shown in Figure 2-11. When we send a digital number “1″ at serial port, then we can receive “1″ at wifi network. Similarly, if sending “1″ at wifi networks, we can receive “1″ at serial port. Thus, we have realized the normal communication between serial port and wifi network.

    Figure 2-10 WIFI connection based on Arduino shield board

    Figure 2-11 Communication between serial port and wifi network

Seg 2: Relevant Concepts

4.3 Experimental principle

Before presenting the experiment principle, some relevant concepts should be given out firstly.

Digital signal: its means that its amplitude is discrete, and limited into a range, like binary code used widely in computer science. The digital signal has a strong anti-interference ability, and can be easily processed by digital signal processing. Nowadays, there are many digital signals, such as mobile signal, information handling by computer, and so on.

Analog signal: its ware changes continuously. Theoretically, we can get any of the value from the analog signal. Since it is interfered easily by the other signals, it is difficult to handling. Thus, generally, the analog signal should firstly be transformed into the digital signal for the convenient signal processing. The difference could be shown in Figure 4-1.

Figure 4-1 Difference of digital and analog signals

PWM is the abbreviation of Pulse Width Modulation. It means that we can equivalently get the required signal wave on the basis of a series pulse width, as shown in Figure 4-2. We can achieve a sine signal wave by a series of pulse signal by the different width. In fact, this principle can be illustrated by the equivalent area from mathematical integral. For example, the area of the first pulse is equivalent to the area surrounded by sine signal wave. So, we can change the duty cycle to get the voltage signal wave. Please image it. If we want to get a direct current voltage wave, the width of each pulse should be equal. In addition, PWM technique has been widely applied to the motor speed control, valve control, and so on. For example, PWM has been used to electronic cars.

Figure 4-2 Sine wave by PWM