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New board design: additional I2C gadgeteer socket


#1

I’m doing a new board design based on the G120 module and cobra II schematics and I need an additional I socket (I2C). Can I just place an additional gadgeteer socket connected with the already existing T/I socket? Or do I need to something more?


#2

You need the 2 i2c pins plus 2 additional gpios. Please check the socket map.


#3

Thx Gus, an other question regarding SPI

As I saw in the schematic of the cobra II net board, the ENC interface and the S socket share the same SPI interface (2). Can I use this same SPI interface for a flash (mem) chip (spi based)? I think it can… but can anyone confirm this?

How many SPI device can be used on one single SPI interface?


#4

You can use any spi device as long as it has chip select pin.


#5

whoow,. that’s fast. I guess you’re in some kind of polling state :slight_smile:

Thx again!!


#6

@ andre.m - there might be a limit on how many devices the master can drive. depends upon what type of logic is used.


#7

Don’t forget about CS pins for each device.


#8

there are lots of different types of logic chip technologies. for example the TTL families. a standard 5v TTL chip can drive 10 standard 5v TTL chips.


#9

A quick and maybe a silly question: :slight_smile:

Designing my first board with eagle cad. When placing, for example, an ethernet jack do I need to create the mounting holes myself or will it be done automatically when placing the part?


#10

@ andre.m - http://en.wikipedia.org/wiki/Fan-out


#11

that totally depends on the part. You should edit the part to check if it includes all necessary mounting (they usually would, but if it was a part from a custom library to start with, you can only trust the part’s creator so far :slight_smile: )


#12

As Brett says, it depends on who created the part and if they added all the right holes.

One thing you will quickly learn as you progress in PCB design and that is not to trust any library parts without going over them meticulously with a fine tooth comb! Even manufacturers provides parts have been know to be wrong :slight_smile: Having been bitten a few of times in the past with incorrect foot prints or wrong pin definitions, I now only use library pats I either created myself or ones I have copied and given a thorough check over.

On a side note, if you are going to be laying out Ethernet, pay careful attention to the Ethernet requirements for PCB layout. The RX/TX pairs should ideally be done with differential layout and impedance matching. It may not sound like much, but if your tracks are not done correctly, you can run into trouble with signal timing and this can have a big effect on the connected device and getting things to work. Same with USB by the way. If your tracks are very short you are most likely to be OK, but worth paying attention to anyway.


#13

Brett & Dave thanks for the response. I’ll check the parts. Although I copied them from the cobra II schematics I’ll check them.

Thx for the side note also, I’ll keep it in mind. The implementation of the ethernet en usb parts will be like the cobra II design.


#14

As I’ve copied the ethernet part from the cobra II schematic and used it in my own design I’m getting my parts together for assembly. But I can’t find the connector :frowning:

Where can I get the Ethernet connector as been used on the cobra II board? Or any advice on an alternate with same specs?


#15

http://www.digikey.com/product-search/en?x=-1115&y=-73&lang=en&site=us&KeyWords=J00-0045NL


#16

Thx, I’ll get a couple of these. :slight_smile: