A countdown counter with the MAX7221 and a seven-segment display
Days until Christmas, time until retirement: We count the days to many events in life. A countdown counter can help make the time to wait fly by and increase anticipation. In this article, I show you how to use the Raspberry Pi as a control unit to build a chic countdown counter based on an LED segment display.
To ensure that the countdown can be seen from a distance easily, a large seven-segment Kingbright SC08-11SRWA [1] display (20.32mm/0.8 inch high) is used to display the remaining days to an event. The LEDs use a common cathode, which makes the display compatible with a MAX7221 display driver.
The combination of parts used here requires the use of a soldering iron. Completely assembled modules that match the capabilities of the MAX7221 are available, but they have considerably smaller displays of (typically) eight digits. Four digits should be enough for a day countdown (i.e., 9,999 days or more than 27 years). If you really want to count down for a longer period of time, simply add an additional segment to the setup.
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