Pinball: Matrix LEDs (Part 1)

In the previous post I talked in detail about driving LEDs using the PSoC4 BLE GPIOs.  The basic problem that I have now is that I want to drive way more LEDs than I have available GPIO pins.  Using one GPIO per LED means that I am only able to drive 8 LEDs with the 8 pins that I have reserved.  But I want to do 16 not 8.  So now what?  To solve this, I configure the LEDs into the Matrix.  In the schematic below you can see an example 3×3 test matrix.  It uses 6 pins and is able to drive 9 LEDs.

So how does it work?  Simple.  Write a 1 onto the row you want to enable then write a 0 onto the other rows.  Next write a 0 onto the column you want to enable and a 1 onto the other columns.  For example, if I drive 010 onto the “row” pins and 101 onto the column pins then the LED I have labeled 1,1 will turn on.  With this scheme the row pins are used to drive the “power” and the column pins are used to drive the “ground”.

Then I get the lab assistant a.k.a. 12 year old son Nicholas to build up a test board.

I need a little bit of firmware to turn on each LED one by one.

• Lines 17-19: iterate through the three rows/columns
• Line 23: write the correct pattern to the row driver (001,010,100)
• Line 21-22: print the current row column to the UART
• Line 24: write the correct pattern to the column driver (110,101,011)

After that everything seems to work… you can see how bright the LEDs are in the movie below.

In the next post I will show you how to Time Division Multiplex the LEDs and explain what the problem is with that scheme.

You can find all of the source code and files at the IOTEXPERT site on github.