How to use a multimeter to determine whether the digital tube is a common cathode or a common anode

　　1. What is a digital tube?

　　A digital tube is a display device composed of multiple light-emitting diodes. According to the number of segments, it can be divided into seven-segment tubes, eight-segment tubes, and M-shaped tubes. According to the working mode, it can be divided into common anode digital tubes and common cathode digital tubes. According to the number of digits, it can be divided into 1-digit, 2-digit, 3-digit, 4-digit, etc. According to the color, there are red, green, blue, etc., and according to the size, it can be divided into 0.28 inches, 0.30 inches, 0.36 inches, etc.

　　2. Working Principle of Digital Tube

　　A digital tube is a semiconductor light-emitting device, and its basic unit is a light-emitting diode. A digital tube that can display 4 digits is called a four-digit digital tube. Of course, there are digital tubes with multiple digits and digital tubes with only one digit, and their electrical principles are the same. Digital tubes are divided into seven-segment digital tubes and eight-segment digital tubes according to the number of segments. The eight-segment digital tube has one more light-emitting diode unit than the seven-segment digital tube (one more decimal point display); according to the connection method of the light-emitting diode unit, it is divided into a common anode digital tube and a common cathode digital tube. A common anode digital tube refers to a digital tube in which the anodes of all light-emitting diodes are connected together to form a common anode (COM). When a common anode digital tube is used, the common pole COM should be connected to +5V. When the cathode of a certain field light-emitting diode is at a low level, the corresponding field is lit. When the cathode of a certain field is at a high level, the corresponding field is not lit. A common cathode digital tube refers to a digital tube in which the cathodes of all light-emitting diodes are connected together to form a common cathode (COM). When a common cathode digital tube is used, the common pole COM should be connected to the ground wire GND. When the anode of a certain field light-emitting diode is at a high level, the corresponding field is lit. When the anode of a certain field is at a low level, the corresponding field will not light up.

　　3. Electrical characteristics of digital tubes

　　The single-digit digital tube has ten pins, 8 of which are used to light up a, b, c, d, e, f, dp, a total of 8 light-emitting diodes (introduced in the principle), and pins 3 and 8 are common COM pins, which are connected and have the same function, and can be connected to any one of them. For a clearer introduction, the following figure is attached:

　　4. Classification of digital tubes

　　According to the connection method of the light-emitting diode unit, it can be divided into common anode digital tube and common cathode digital tube. Common anode digital tube refers to a digital tube in which the anodes of all light-emitting diodes are connected together to form a common anode (COM). When the common anode digital tube is used, the common pole COM should be connected to +5V. When the cathode of the light-emitting diode in a certain field is at a low level, the corresponding field will light up. When the cathode of a certain field is at a high level, the corresponding field will not light up. Common cathode digital tube refers to a digital tube in which the cathodes of all light-emitting diodes are connected together to form a common cathode (COM). When the common cathode digital tube is used, the common pole COM should be connected to the ground wire GND. When the anode of the light-emitting diode in a certain field is at a high level, the corresponding field will light up. When the anode of a certain field is at a low level, the corresponding field will not light up.