I'd like to ask for some advice on the circuit described below:
I'm building a matrix of multiplexed seven segment displays, with common anode. The ports D1-D3 and segments A-DP will be driven by I/O pins from an LPC1114 ARM microcontroller.
As I understand the datasheet specs for this part I cannot exceed 4mA of source or sink current in the standard purpose I/Os. See this question for more clearance on this.
The display datasheet says that the forward voltage of each segment of the display is about 2.10V. They will be feed with 3.3V. I want use 10mA of current in each segment (I believe it will give a nice brightness with this current).
With all this in mind, and for what I understand of electronics, I aks these questions:
1 - I cannot connect the segments A-DP directly to I/O ports since it will exceed the sink capabilities of the I/O. Is this correct?
2 - Almost all schematics I found on the web on multiplexed displays do that. I did not found anyone that deals with this problem. What suggestions do you have to make it possible to sink more current in each display segment?
3 - I thought that maybe I could sink segments A-DP to ground using a MOSFET controlled by I/Os. Is this a good idea? What do you think? Any schematics on this?