nelson
Posts: 38
Joined: Sat Dec 17, 2011 3:43 am

Standard i2c only connector

Mon Feb 11, 2013 11:02 pm

Hi,

Have seen some boards online (extra io, relays, etc) and the connectors used for cascading boards don't match with each other. Could we have an agreement on a small connector to be used across all our custom boards, sanctioned by the foundation? Would like to recommend a header matching the first 6 pins of the pi header. Perhaps also updating the io wiki page to reflect whatever choice is made here.
Attachments
Screenshot.png
proposed 1
Screenshot.png (3.28 KiB) Viewed 2679 times

techpaul
Posts: 1512
Joined: Sat Jul 14, 2012 6:40 pm
Location: Reading, UK
Contact: Website

Re: Standard i2c only connector

Tue Feb 12, 2013 3:15 pm

There is NO standard I2C connector as there never has been since the inception of I2C in the 1990's.

There are so few wires it has not been necessary as the majority of applications do not support hot-swpa and have NO connectors.

I dont see why you are trying to do something un-necessary
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

repton
Posts: 91
Joined: Sat Mar 17, 2012 6:06 pm
Location: North Yorkshire, UK.
Contact: Website

Re: Standard i2c only connector

Tue Feb 12, 2013 3:30 pm

techpaul wrote:I dont see why you are trying to do something un-necessary
I don't think it is unnecessary. The OP's point is that with many people offering add-on boards that sit over the I2C pins on the GPIO connector and given the very nature of I2C that multiple devices can be connected to the bus we could do with some kind of "standard" to allow the various manufacturers boards to be connected to the Pi at the same time without involving lots of messing about.

Some folk already have this covered. AB Electronics, for example, provide their boards with long pins to allow them to stack on top of each other and my own RPI3 1-Wire Master board will feature the same type of connector so that it doesn't monopolise the GPIO connector. It could be that this is all that is needed but it will mean some boards end up much larger than is really needed as having a 2x13 connector when you only want a few pins at one end is in some ways less than ideal.

Paul
UK Supplier of 1-Wire components, kits and modules:
http://www.sheepwalkelectronics.co.uk/

techpaul
Posts: 1512
Joined: Sat Jul 14, 2012 6:40 pm
Location: Reading, UK
Contact: Website

Re: Standard i2c only connector

Tue Feb 12, 2013 3:32 pm

So you already have a standard use a 2 x 3 way boxed header that does not affect the other pins

The only 'standard' part is the arrangement of the signals on the pins which foundation I believe have said will not change.

You have enough of a standard already.
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

techpaul
Posts: 1512
Joined: Sat Jul 14, 2012 6:40 pm
Location: Reading, UK
Contact: Website

Re: Standard i2c only connector

Tue Feb 12, 2013 9:18 pm

Also remember we actually have two different connectors for I2C on the Pi as P1 and P5 have I2C on it.

Are you suggesting we should have Rev 3 so all I2C connectors are the same?
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

nelson
Posts: 38
Joined: Sat Dec 17, 2011 3:43 am

Re: Standard i2c only connector

Thu Feb 14, 2013 7:01 pm

It's not about changing the pins on the raspi itself, it's about we all agreeing on a standard connector to use on add-on boards, ideally we could get to be like the arduino in that every arduino made is compatible with (almost) every shield made, seeing repton post i agree that a stackable header on the boards is a good idea and should be something that vendors should supply so beginners could stack boards.

So ideally all add-on boards should have for maximum compatibility:
  • Use the standard raspi connector with stackable header.
  • If there really is a need for a smaller connector use the pin-out for the first 6 pins on the raspi connector
  • Do not use the 3v3 rail and instead generate it from the 5v as the 50ma on 3v3 can easily get over used while stacking different boards.
  • If SPI is used supply a method to choose different CS pins
  • If I2C is used supply a method to choose different addresses
This is turning more into a best practices for board developers, but would really like more opinions from the forum users on improvements, will definitely use repton's idea on my custom boards.

techpaul
Posts: 1512
Joined: Sat Jul 14, 2012 6:40 pm
Location: Reading, UK
Contact: Website

Re: Standard i2c only connector

Thu Feb 14, 2013 8:32 pm

nelson wrote:It's not about changing the pins on the raspi itself, it's about we all agreeing on a standard connector to use on add-on boards, ideally we could get to be like the arduino in that every arduino made is compatible with (almost) every shield made, seeing repton post i agree that a stackable header on the boards is a good idea and should be something that vendors should supply so beginners could stack boards.

So ideally all add-on boards should have for maximum compatibility:
  • Use the standard raspi connector with stackable header.
There are TWO connectors on the Pi giving I2C with different pinouts as of Rev 2.0
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/

User avatar
johnbeetem
Posts: 945
Joined: Mon Oct 17, 2011 11:18 pm
Location: The Mountains
Contact: Website

Re: Standard i2c only connector

Thu Feb 14, 2013 8:57 pm

I'd suggest using an existing standard, such as Digilent's Pmod (TM) spec. I've never used it myself, and I don't have any relationship with Digilent.

Digilent Pmods: http://www.digilentinc.com/Pmods

License and link to spec: http://www.digilentinc.com/Pmods/licensing.cfm

User avatar
Defiant
Posts: 179
Joined: Tue Oct 30, 2012 6:17 pm
Location: Hamburg, Germany

Re: Standard i2c only connector

Sat Feb 16, 2013 7:31 am

For I2C I just use a 1x4 2.54mm header, because I can easily connect multiple together on a Stripboard:

Code: Select all

Vcc Gnd SDA SCL
 |   |   |   |
Vcc Gnd SDA SCL
 |   |   |   |
...

Return to “Interfacing (DSI, CSI, I2C, etc.)”