I am currently doing a LED Display board consisting 4 sets of 5x7 LED display. I not very sure how do I connect the LED display board with the mbed so that it will display 1 number or character in each display. I would also need some guidance of how do i write a program for it. Hope you guys can help me through.. Thanks (:
You probably want to use some form of multiplexing the 4 digits to save on pins. The most common approach is to use external hardware shiftregisters to activate one row of LEDs in one go and multiplex the rows sequentially. In your case you would have 7 rows and 4x5=20 LEDs per row. The shiftregisters can drive the 20 LEDs directly. You do need a driver transistor per row (so 7 in total).
You could also choose to activate one column of 7 LEDs at a time and multiplex across all 20 columns.
In this case the shiftregister drives the 7 LEDs directly, but you need a driver transistor for each column (20 in total). This solution is therefore more expensive.
Suitable schematics have been published many times. The mbed can drive the shiftregister solution by using the SPI port. I have just published an example for control of a multiplexed 14 segment 4 digit LED display. Have a look at my code to see how its done.
You will have to modify the code to store and multiplex a bitmap that represents the desired characters or symbols.
I am using LED for the display, the programming is the same as 7 segment? sorry for asking such newbie question.
I think that these two examples become your reference.
seven segment dynamic drive
16*16 2color dot matrix led drive
The design makes use of HT1632C and save a lot of pin from your mbed.
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mbed, the fastest way to prototype with ARM based microcontrollers.
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