TLE / ICT Q3

• Photoresistor is a light-sensitive resistor. When the strength that light casts onto the photoresistor surface is not the same, the resistance of the photoresistor will change. With this feature, we can use photoresistor to detect light intensity. The photoresistor and symbol are as follows.

  
• In this circuit, when photoresistor resistance changes due to light intensity, voltage between photoresistor and resistor R1 will change, so light intensity can be obtained by measuring the voltage.

  
• Servo is an auto-control system, consisting of DC motor, reduction gear, sensor and control circuit. Usually, it can rotate in the range of 180 degrees. Servo can output larger torque and is widely used in model airplane, robot and so on. It has three lines, including two for electric power line positive (2-VCC, red), negative (3-GND, brown), and the signal line (1-Signal, orange).

  
• A DC motor is an electrical machine that converts electrical energy into mechanical energy.

  
• Torque is a measure of the force that can cause an object to rotate about an axis. Just as force is what causes an object to accelerate in linear kinematics, torque is what causes an object to acquire angular acceleration. Torque is a vector quantity.

  The more torque, the greater amount of power an engine can produce. If your engine has a lot of torque, your car can accelerate more quickly when the vehicle is beginning to start. Torque is also important when your car is performing hard work such as moving heavy loads or climbing a steep hill.

  
• We use 50Hz PWM signal with a duty cycle in a certain range to drive the servo. The lasting time 0.5ms-2.5ms of PWM single cycle high level corresponds to the servo angle 0 degrees - 180 degrees linearly. Part of the corresponding values are as follows:

  
• Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off.
• When you change the servo signal, servo will rotate to the designated position.

  
• Use D3 of Arduino UNO to drive the servo. Pay attention to the color of the servo lead wire: VCC (red), GND (brown), and signal line (orange). The wrong connection can cause damage to the servo.

  
• The hexadecimal number system is a type of number system, that has a base value equal to 16. Hexadecimal numbers are represented by only 16 symbols. These symbols or values are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F. Each digit represents a decimal value.
• The conversion between binary and decimal systems has been mentioned before. When you write the code, the number is decimal by default. Hexadecimal numbers need to add the 0x prefix in the code, such as 0x01. One Hexadecimal bit can present one number between 0-15. To facilitate writing, numbers greater than 9 are written into the letter A-F (case-insensitive) such as 0x2A. The corresponding relationship is as follows:

  
• Conversion between hexadecimal and decimal systems is similar to the conversion between hexadecimal and binary such as the sixteen-digit 0x12:

  
• When a hexadecimal number needs to be converted to a decimal number, first, the nth number of it needs to be multiplied by n power of 16, then sum all multiplicative results. Take 0x12 as an example:

  1 *16^1+2*16^0=18

  [^](Wedge Symbol) represent the logical and operator
• When a decimal number is converted to a hexadecimal number, the decimal number is divided by 16. Then we will get the quotient and remainder, and the quotient obtained will be continuously divided by 16 until the quotient is zero. Arrange all remainders from right to left in a line. Then we complete the conversion. For example:

  
• The result is of the conversion 0x12. When you write code, sometimes it is convenient to use hexadecimal, especially involving bit operation, because 1 hexadecimal number can be expressed by 4 binary numbers (2^4=16). The corresponding relationship between 4 bit binary numbers and 1 hexadecimal number is shown as follows:

  
• 74HC595 Chip - used to convert serial data into parallel data. 74HC595 can convert the serial data of one byte to 8 bits, and send its corresponding level to the corresponding 8 ports. With this feature, 74HC595 can be used to expand the IO port of Arduino board. At least 3 ports on the Arduino board are need to control 8 ports of 74HC595.
• The ports of 74HC595 are described as follows:

  A) 12

  B) Serial data

  C) MR

  
• Led Matrix is a rectangular display module that consists of several LEDs. The following is an 8*8 monochrome LED matrix with 64 LEDs (8 rows and 8 columns).

  
• In order to facilitate the operation and save the ports, positive pole of LEDs in each row and negative pole of LEDs in each column are respectively connected together inside LED matrix module, which is called Common Anode. There is another form. Negative pole of LEDs in each row and positive pole of LEDs in each column are respectively connected together, which is called Common Cathode.
• Common Anode displays have all the LED Anodes connected together and need a display driver with outputs which become low to turn each segment on. Common Cathode displays have all the LED cathodes connected together and need a driver with outputs that become high to turn each segment on.