This article will be about dot matrix display that I bought for a replica of antimatter explosives from FRINGE. Again, it will be controlled by the Arduino.
Dot matrix, as the name suggests, is display made up of a network of LEDs. You can find similar for example in trams or metro. There are a great many types, from the very primitive to intelligent displays with a memory.
The display may have in addition to the number of characters also different number of rows and columns. For example, 5x7 means that you can render the letters or numbers on the network with 5 columns and 7 rows. We turn on therefore only those points that will represent the character. So you can enclose on squared paper 5x7 rectangle and then paint the squares shapes as a letter, number or whatever you need. The rendered squares represent the LEDs that will be ON, you therefore have a value of 1, others (LEDs that will be OFF) are 0.
Depending on the type of the display and its datasheet, it is necessary to convert these values correctly. Either overwrite the columns or rows. If we rewrite the column to display the letter F, there will be all LEDs lighted at the first column, therefore it will be a 7 ones numbers. You will be overwritten from the bottom up as 1111111 and this binary value is converted to hexadecimal. You can use online converters, 1111111 is in hexadecimal 7F. So we write it as 0x7F. The second column is from the bottom 0001001, after conversion it is 9 and we will write it as 0x09. We will do the same with other columns. The entire entry for the letter F will be “0x7F, 0x09, 0x09, 0x09, 0x01”. This was the example for 5x7 display.
I bought Siemens SCDQ5581 5x5 display that has a length of 8 characters. Rendering will be similar except of that we will overwrite lines and not columns. You can even pre-define these characters in the library, so you do not have to write it later using these hexa numbers. This is a big advantage, because then you can just define the time you want to write or some text in the form “Hello World!” and you do not have to worry about more. These libraries can be even found already predefined, so you can save even more time and work. For a long time I could not find a whole library of controlling SCDQ types of displays. But eventually I found one here:
You can look at the result on the first video you will see scrolling text and the countdown and then …. 🙂
Last modification consisted of small colon and dot flashing exactly as it was seen in the episode 5x04 – The bullet that saved the world. Then they can come further additions, such as in the last added videos possibility of setting countdown time (can be set from 15 seconds to 2 minutes in 15 second intervals).