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LED Matrix Clock

It's been a while since I've updated this site. There was too much going on with school at the time and I just didn't end up getting time to write projects up. I graduated a while ago now and have more free time, so I'm going to make an effort to post here again. Starting off with a small project:

I have been moving my PCB design work over to OrCAD this year and needed a simple test project to learn the workflow in the new software. Adafruit has some neat looking LED matrix modules that I wanted to use somehow. This was the result:

Finished clock.

The above photo was taken before I implemented brightness control. It is dimmed to be a bit less blinding now. The electronics are pretty simple. A STM32F0 microcontroller controls everything. Three 74HC595 shift registers drive the columns and a ULN2003 transistor array is used to switch the rows. The LEDs all run directly off 5V input power and the micro is supplied by a 3.3V regulator.

PCB side of the clock.

I made the mistake of designing around a ULN2803 (8 channels vs 7 on the ULN2003) without realizing that they come in a wide SOIC package. Ended up using a ULN2003 plus a SOT23 FET for the 8th channel to make it work. In addition, I tied the BOOT0 pin on the micro to VCC instead of GND, which forced it into bootloader mode instead of running my code. A lifted pin and another jumper wire fixed that.