5x7 LED Display Driver Schematic and PCB Design

Here are the data files from the EAGLE Layout Editor:

• display57.sch: The schematic (EAGLE format)
• display57.brd: The board layout (EAGLE format)
• display57.sol: The solder-side artwork (Gerber format)
• display57sol.plt: The solder-side outline (in HPGL format; created by the "Translate Gerber files to HPGL" section of PCBMill Web Utilities 0.96)
• display57.drd: The drill data (NC drill format)

I had to create my own part for the 5x7 LED matrix display. Here is the EAGLE library: ledmatrix.lbr. I found the LibExtract utility (in the CadSoft Miscellaneous Download area at ftp://ftp.cadsoft.de/pub/userfiles/misc/libextract.zip) was very useful in getting started. The procedure was:

1. From the EAGLE Control Panel, File:Open:Library.
2. From the EAGLE Library window, File:Export:Script to "tmp.scr"
3. Use LibExtractor to read "tmp.scr" and create "tmp2.scr", a script that contains only the device (packages and symbol) that I want to use as the basis for my new part.
4. From the EAGLE Control Panel, File:New:Library.
5. From the EAGLE Library window, File:Script and select "tmp2.scr".
6. Use Library:Package and Library:Symbol to modify the device into the new device. (Also note that you can edit tmp2.scr with a text editor, but that gets involved.)

In the process of creating the schematic, I learned a few things about EAGLE and posted them to IkonBoard:

1. Use View:Redraw (or F2) to update the display. As you move things around, they leave turds behind that can fool you if you're not careful.
2. Use Tools:ERC (Electrical Rules Check) to check your schematic before you start layout. I had a schematic that looked ok, but the board layout was missing traces. It turns out there were places where I thought I had made connections, but I had only laid the wires over each other. Once I fixed the ERC errors and warnings, the board layout went much better.
3. The PIC16F876P chip expects you to use VDD and VSS, not VCC and GND. So, if you use VCC and GND as I have, ERC reports warnings like:
   WARNING: Sheet 1/1: POWER Pin IC1 VSS connected to GND
   WARNING: Sheet 1/1: POWER Pin IC1 VDD connected to VCC
   WARNING: Sheet 1/1: POWER Pin IC1 VSS connected to GND
   I suspect the warnings are harmless.
If you do use VDD and VSS, be warned that if you also use other ICs (such as the MAX232 serial transceiver), ERC will complain that you have not made connections for that IC's implicit VCC and GND pins. I have not yet found a way to reconcile these differences. For now, I am going to live with the warnings from the PIC chip.