Preparing v.03 SMD and THT

A project log for ╬╝Diff: Long distance digital signals over RJ45

A simple 50mmx44mm module to route power and differential signals (RS-485) over RJ-45

Alexander WilliamsAlexander Williams 04/20/2021 at 04:450 Comments

I've cloned the v.03 though-hole (THT) board and replaced the footprints of many through-hole components with SMD parts.

Here's the through-hole v.03 preview so far:

The board size and layout will remain identical in the SMD version, except for slightly different placement of the SMD components. This means it will be possible to mix and stack the SMD/THT boards, and connect them using the same cable assemblies without any pin mix-up between them.

We do end up with lots of "wasted space" on the SMD board. I think it's not a big deal.

The SMD components are much cheaper too, but the SMD assembly will bring the cost back up.

I'm currently still trying to decide if I want the fab to hand-solder certain components as well (IC DIP socket, RJ45 connector, JST connector). Just those three components have 22 solder points combined. I'll need to compare the cost VS time saved for hand soldering.

Since there's so much free space on the board, I'm using all 0805 resistors and capacitors with large hand-soldering pads so it'll be easier to replace them with different values if needed.

The 5V switching voltage regulator, fuse, and 120ohm terminating resistor will remain through-hole and need to be manually soldered. That provides some flexibility on how much current the board can pull, and whether it's used in a bus topology or not.

At the last minute, I also added an SMD diode between the fuse and VIN, which should protect the board/components in the event of user error.

I'm still waiting for the v.02 boards to arrive before sending v.03 to the fab.