Pulling my hair again over the i2c connectors !
Coming from a software background I prefer a digital interface - particularly I2C.
Over the past couple of years I have purchased a variety of sensors and other devices with i2c … but when I connect them up comes the headache ! Some use Grove 2mm connector, others use Gravity 2mm (different pinout) and then there’s the small 1mm connectors.
I found there are come commonalities.
I am just using 3v3, so for me they fall into 3 groups. Firstly there are 3 varieties using 2mm pin pitch connectors The Grove connector is similar and can sometimes be adjusted to fit. Watch out for Gravity with the pairs of pins swapped!, thus DFRobot’s Gravity becomes a group by itself.
| Name |
Connector |
pin1 |
pin2 |
pin3 |
pin4 |
| STEMMA |
JST PH 2.0mm |
GND |
3v3/5v |
SDA (white) |
SCL (green) |
| Grove |
A205 series 2mm |
GND |
3v3/5v |
SDA (white) |
SCL (yellow) |
| Gravity |
JST PH 2.0mm |
3v3/5v |
GND |
SCL (blue) |
SDA (green) |
Then to make boards smaller, we got smaller connectors. Fortunately they all use the same JST PH 1mm connectors, and the same pin sequence - making them interchangeable.
| Name |
Connector |
pin1 |
pin2 |
pin3 |
pin4 |
| Qwiic |
JST SH 1.0mm |
GND |
3v3 |
SDA (blue) |
SCL (yellow) |
| STEMMA QT |
JST SH 1.0mm |
GND |
3v3/5v |
SDA |
SCL |
| picodev |
JST SH 1.0mm |
GND |
3v3 |
SDA (blue) |
SCL (yellow) |
That’s all very well at the device end … but at the other end of the cable there’s not much help. Options are:
- same connector (generally another female)
- dupont pins for breadboard
- bare wires for soldering
There is almost nothing to connect between the different systems, other than breadboard. I have found only one cable SKU: CAB-28768 for Qwiic to Gravity, and the ADA4424 to connect 2mm STEMMA with 1mm STEMMA QT.
There are hubs for each of these three cable standards - but nothing which incorporates and links them. I see this as a gap in the market - but what specs for a product to fill it ? How many of each ?
- 3 picodev/Qwiic/STEMMA QT connectors of JST SH 1.0mm with sequence GND | 3v3 | SDA | SCL
- 3 STEMMA/Grove connectors of JST PH 2.0mm with pin sequence GND | 3v3/5v | SDA | SCL
- 2 rows of female dupont sockets with sequence GND | 3v3 | SDA | SCL
- a bit of a gap to separate, and for the PCB traces to swap over (or maybe to go around and come from other end)
- 3 rows of Gravity JST PH 2.0mm connector with sequence 3v3/5v | GND | SCL | SDA
Hi Donald
Interesting and a good comparison. What happened to the “Standards” people of times past. I have lost touch over the past 25 years due to many things but I think there were a few organisations that looked after such things. Some bits took some time to become internationally recognised but seemed to gradually be accepted in the international community.
Like video recording. VHS and BETA. VHS seemed to become the domestic “standard” while BETA was used in the TV station world, in Australia anyway. TV stations had some VHS machines mainly to provide domestic playable tapes to interested parties like an interviewed person etc.
Along came digital and in the case of audio many proposals for a “standard” . At least the attempt was made at “standards” but it dragged on for too long and a couple of companies like Sony and Phillips went ahead and produced their own “standard”. This became SPDIF (Sony,Phillips Digital InterFace) which over time became some sort of “standard” due I think to general use.
But with the world shrinking particularly in the distribution of Electronic type components (Which is of concern to us) and so many Companies and indeed Countries involved I think this “Standards” business has once again become scrambled.
Unfortunately for us mere mortals this multitude of “Standards” has become somewhat of the norm. Almost impossible for the individual to keep track all but the ones we are currently interested in, such as your interest in I2C connections. I personally have not spotted this having not much to do with the various systems. My usage has led me to note what the connections are and not so much what pin number is involved so these discrepancies have slipped by.
Regarding connectors of which you have listed a few of interest to you. Have a thought for the people servicing different equipments using different connector “standards”. How many test cables do you think they will need. The multitude of Co-Ax connectors can be a nightmare. BNC-50Ω and 75Ω. Type N-50Ω, 75Ω and 60Ω and PL259/SO239 With SMA and the other miniature ones would be the more common. But in the real RF world there are others. General Radio (GR), Spinner and Desifix come to mind and there undoubtedly others.
Anyway, happy sorting.
Cheers Bob
PS: GR and Desifix are “sexless”, ie; no different male and female, which makes things a bit easier.
In that mix above there is TNC which is basically BNC with a threaded retaining nut, Twinax which has twin conductors and Triax which has 2 separated screens used for carrying power and signal over a single cable to a TV studio camera.
Thanks…
I have tried to move on from what uses what and do the pin mapping at benchtop time. I now get the bits I think are best fit for purpose; which is where I suspect the challenges start. i.e we tend to use pre-built modules as such its the module designer that is picking the connectors to fit the board layout or their internal standard.
So I now have some “cable kits” that have all sorts of connector size and housing… I then make the lead to connect from the module to what I want to use. I tend to stick to the stock 2.5mm headers while testing and play, then move to whats fit for purpose if/when we get off the bench to so pseudo production or an actual production. I have a whole tray of 2.54mm housings and contracts, so single row of 4 no problem, then crimp to the end of the cable the fits the board.
I now try to think think of this more inline with “if I made it from the ground up”, then I would need to pick a connector to use and I could make my own “standard” them I could break that standard … yeah… I know… But my issue with some connectors is just usability in target project environment (dupont are nice and fast, but dont always have the best grip… JST may be nice and fit well, but do the tiny ones have enough current capacity or do I run a separate power connector…
I guess my key point is… I think it can be hard to get a cheapish and best fit connector that will remain a standard in the maker marked. So expect it not to fit and have a way to deal with it 
side note: Over the years some of my go to connectors are not even made anymore. I still have a tray of HE14 connectors that I really liked, but not so easy to buy now, so should not be used in new projects.
