woot 1st PCB for MCP23S17 gpio/led driver

:) Finally got the courage to design my own PCB from scratch. It's basically a breakout for 2 * 16 channel GPIO MCP23S17 extenders. So the I/O pins lined up I decided to mount the 2nd IC on the reverse side so the main signal wires can be kept nice and straight and to avoid unnecessary rat nests.


It has the ability to chain boards together and I went with solder pads to allow the address of the chips to be selected rather than hard coded. The 16 pins of each chip are in groups of 3 to make it easier if using RGB LEDs. This chip has no PWM but is very cheap and comes in the easy to solder (so be it larger) DIP size. The 7 different color combinations + all off is perfect for my needs and budget.

To make it more flexible no resistors are added to the board... these would be added in-line on the wiring.

I'll can make the schematic etc available at some point when the board has been tested.

The circuit has a single protection diode which seemed to work on the breadboard. Was wondering if I should bother with a capacitor between VCC and GND... I suppose if I make space for it they can be optional.

Well done. I really like the idea of the flipped chip to make the PCB-layout more manageable :D

Can you post a link to a place where to download your .BRD-file if anyone else wants to give it a go?

// Per.

Yes, add cap from VCC to Gnd for each chip. 0.1uF, close to VCC pin. Add pads for current limit resistors. Folks can use "inner" pads for situation with no resistor, or "outer" pads when resistor mounts on the boards: chip leg pad - resistor pad 1 - resistor pad 2 - LED pad. Case 1 - no resistor; connect to resistor pad 1. Case 2 - resistor used; connect to LED pad.

And some mounting holes.

Thanks for all the positive feedback :) . Since posting I had modified to add 2 capacitors between VCC/GND on each chip.

I'll also look at making it so optional resistors can be put in place on the board. I originally had this but it made the board quite a bit larger. I also wasn't too sure if mounting one IC on the reverse side was acceptable but did it to keep the data lines simple/straight.

I will attach the brd and schematic soonish so others can utilize it if needed.

Latest had a single mounting hole in the middle :o

Is that a zener diode from ground to ground? I think I'm missing something.

You placed the part, routed the traces, and then moved it. That looks like crap, and if you're going to be showing the boards to others, or selling them, they will judge you for it. If you care, rip up the traces that are at odd angles and redo them.

One mounting hole? You have plenty of board space for more than one. The hole you have is huge - larger than you probably want. I normally size holes for a #4 screw, though a #6 may be more convenient, since 6-32 screws are so abundant.