Computer Systems Experiments 18 | Persistence of Vision and Displaying Multiple Digits…

Computer Systems Experiments 18 | Persistence of Vision and Displaying Multiple Digits Simultaneously

You may have a question about the 7-segment display. That is we can not actually display two different digits at the same time based on the structure of this electronic component. For example, you can display 1111, 111, 11, or 11 but we can not display 1234 other numbers with multiple digits.

However, the good news is — we are almost there! Before we learn about how to display digits simultaneously, we have to know about the concept called the persistence of vision. It refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye. This concept is widely used for animations, movies, and video games.

So our idea to display multiple digits is by shortening the DELAY time as much as possible. In the last experiment, the delay time is set to be 0x3f0000. And if we shorten this time to 0x3f000 , let’s see what will happen.

Wow! The speed of counting is boosted and we can hardly tell what is the number at a glance. Now, let’s continue shortening the DELAY time from 0x3f000 to 0x3f00 .

Hooray! Now the persistence of vision is created and we have cheated our eye that the digits are frozen (while actually, they don’t). That’s how we can display multiple digits simultaneously.