Hardware Projects » Misc Hardware Projects

I just did a footprint for SFP cage and connectors referenced above. I'll upload it this afternoon (couple of tweaks left :p)

Added eagle SFP cage and connector. Could use a double check of course :p

mschramm please let's keep the related eagle library / design files in @osmo-small-hardware.git http://git.osmocom.org/osmo-small-hardware/ and make sure to commit frequently. thanks!

A simple PCB has been committed, derived mainly from SFP exoperimenter PCB (see #3313).

Remarks see ticket #3313, some apply here too. - The break in the GND plane under the diff signals of the SFP receptacle is not nice and should be improved on both PCB - if we don't go to a 4-layer PCB (and remain w/ 1.55mm FR4) for a 'closer' GND plane.

13:25 < tnt> Any "real" design using the SFP would be 4 layer, so I guess it's an argument
             to make the experimentation board as close to what a final product would use.

so let's go four-layer. mschramm: please change layer stack-up, add gnd/vcc planes, and adjust trace widths for "usual" four-layer stacking.

let's please also add some form of polarity protection to the DC input. A regular series diode would be the simplest approach, but the TLV1117 requires up to 1.4V drop-out voltage, which makes the budget for 0.7V quite tight. (3.3+1.4=4.7V). Even a shottky diode is unrealistic at that point.

So either we use a different approach for polarity protection, or a different voltage regulator with lower drop-out voltage. Moving away from nominal 5V DC as input voltage is not really a good idea, IMHO.

There are LDOs with built-in reverse polarity protection. However, we cannot use electrolytic caps at the input (C3) in this case. But 10uF at 5V is definitely possible to get as ceramic?

MCP1825ST-3302E would have a maximum drop-out voltage of 0.35V, i.e. allow a series diode. It's readily available and we have used it before (and hence it's in our eagle lib). maybe worth a thought?

SFP+ allows up to 450 mA current to be used by the module.

nm ... I misread the datasheet of that chip, it can do 500 mA ...

for the record: EAGLE designs are in http://git.osmocom.org/osmo-small-hardware/tree/sfp-breakout

PCB revised

• 4 layer stack
• LDO is now a MCP1825
• input protection w/ Schottky series diode and TVS

Some suggestions by tnt still pending (see #3314#note-12), trying to integrate them today.

added features asked by tnt - see #3314#note-15.

Thanks. I extended the default clearance from 0.15mm (was looking quite small in getbv) to 0.25mm, re-ran the DRC and now ordered 10 boards from Seeed.

The clearance change + exported gerber has been committed.

The boards that I have don't have the 3v3 connected on the bottom pin header.

Eagle schematic and board file look fine, but the gerbers are not ...

Also check on the -experimenter board and on that one, the 3v3 is connected.

tnt wrote:

The boards that I have don't have the 3v3 connected on the bottom pin header.

Yes, I'm sorry, that's indeed a known bug :/

Eagle schematic and board file look fine, but the gerbers are not ...

See "git log", the error was fixed after the gerber/boards were made/tested.