LED digital tube dynamic driving experiment

Now let's use the two digital tubes on the experiment board to do an experiment to display the numbers 00 to 99 in a loop. First, complete the necessary hardware part.

Digital tubes are divided into common cathode and common anode types. Both can be driven by microcontrollers, but the driving methods are different, and the corresponding display codes of 0 to 9 are exactly the opposite.

First, let's introduce the single-chip microcomputer driving method of two common anode digital tubes. The circuit is as follows:

Netizens can see that: P2.6 and P2.7 ports control the power supply of tens and ones of the digital tube respectively. When the corresponding port becomes a low level, the corresponding transistor will be turned on, and +5V will supply power to the corresponding bit of the digital tube through the IN4148 diode and the driving transistor. At this time, as long as the P0 port sends out the digital display code, the digital tube can display the number normally.

Because two different digits need to be displayed, a dynamic scanning method must be used. That is, the ones digit is displayed for 1 millisecond first, and then the tens digit is displayed for 1 millisecond, and this cycle continues. In this way, as long as the scanning time is less than 1/50 second, the two different digits will be stably displayed due to the visual residual effect of the human eye.

Next, we will introduce a single-chip microcomputer driving method for common cathode digital tubes. The circuit is as follows:

Netizens can see that +5V directly supplies power to the 8 segments of the digital tube through a 1K resistor, and the P2.6 and P2.7 ports control the power supply of the tens and ones of the digital tube respectively. When the corresponding port becomes low level, the corresponding bit can absorb current. The data output by the P0 port of the microcontroller is equivalent to short-circuiting the digital segments that the digital tube does not want to display to the ground, so that the digital tube will display the required numbers.

Netizens can see that the hardware of common cathode digital tubes is simpler, so in mass production, the hardware overhead is small, PCB area is saved, welding workload is reduced, and overall cost is reduced. Therefore, the use of common cathode digital tubes is more conducive to mass production. The test boards sold now all use common cathode digital tubes.