Multiplexed Display Unit
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Concepts
3 more units of the 7 segment display is wired from the GAL Chip, each common anode of the display will eventually be wired to an output port on the Axman micro-controller.
When multiplexed by a micro-controller, the 7 segment displays will individually turn on each display, and it will do so fast enough so that it will have the appearance of having all 4 display on at the same time. This also means that the micro-controller can change the output of the display in between each time a display is turned on, while the rest is off. The result of this is 4 digits can be cycled through the four displays in sequence, and fast enough so that the 4 display appears like they are displaying difference numbers simultaneously.
In the schematics below, the micro-controller is replaced by a row of pins slots.
When multiplexed by a micro-controller, the 7 segment displays will individually turn on each display, and it will do so fast enough so that it will have the appearance of having all 4 display on at the same time. This also means that the micro-controller can change the output of the display in between each time a display is turned on, while the rest is off. The result of this is 4 digits can be cycled through the four displays in sequence, and fast enough so that the 4 display appears like they are displaying difference numbers simultaneously.
In the schematics below, the micro-controller is replaced by a row of pins slots.
MultiSim schematics for PCB
UltiBoard Layout for PCB
Cycle Frequency
Cycle frequency is the refresh rate of the 4 display. Each time the micro-controller individually refreshes through all 4 each display, its considered as one cycle. Too slow and the display will "flicker", too fast and the display will appears to be to dim.
It appears to be 1360 loops per ms at 20 seconds
at 4.5 ms flicker rate, display appears to be flicker-less
at 4.5 ms flicker rate, display appears to be flicker-less