Question about HWGuy's breakout board on OSH Park

[epicycloid]

I have ordered some of HWGuy's designed Teensy 3.1 breakout boards from OSH Park (version R2), but looking at the parts list, I'm not 100% sure I understand how the optional diode and the pads next to it are intended to work.

Looking at the board/trace drawing, is the diode with the jumper pads, just a clever way to allow connecting a different input voltage to Vin and not backfeeding to Vusb? In the bottom photo the pads at the anode end of the diode are jumpered.

What happens in this scenario when connecting USB power?

Can someone explain this implementation and the permutations?

Thanks,

--Jon

 

[HWGuy]

The red solder jumper has the same function as the one on the Teensy. It connects VUSB to VIN.

to allow connecting a different input voltage to Vin and not backfeeding to Vusb

yes (with the optional diode and the green solder jumper closed (red solder jumper open)). The blue circuit shows how to connect a second input voltage.

 

[epicycloid]

Great, thanks.

Can you give me any insight as to why you picked that specific diode?

Schottky diode SOD-123: Diodes Incorporated B130LAW-7-F (Mouser Part #: 621-B130LAW-F)

And thank you for taking the time to create and share the clever, simple breakout board too. I am really looking forward to getting them and trying them out. They look like they will do exactly what I need to do for this project.

Much appreciated.

--Jon

 

[HWGuy]

The min specs for the diode are:

• IF > 0.5A (USB max current is 0.5A)
• low UF (< 0.4V)
• UR > ~10V (Teensy VIN max voltage is 5.5V)
• PD > 0.2W
• SMD case, solderable by hand

The B130LAW-7-F is my standard Schottky diode and meets all requirements.

 

[epicycloid]

Thank you. Not being an EE I am always trying to learn more about some of the specific component selection criteria (and specs that drive them).

 

[epicycloid]

Some days it just feels like you can't win...

So I received my 12 new R2 breakout boards, and they look great!

And I received a bunch of new purple Teensy's from OSH Park too! How cool is that... and they're the newest 3.2's. Wow.

Oops... one of the features I was really looking forward to is the way the reset is lined up with one of the "mouse hole" cutouts. Finally an easy way to get to the reset on a Teensy 3.x... except that Paul shifted the "rst" pad ever so slightly between the 3.1 and 3.2 layouts. Hopefully I can find some way to use a piece of foil or something like that to make it work.

Other than that little gotcha, the breakout boards look really good and are a brilliant idea! Thank you again for creating and sharing these.