Qwiic / Stemma QT / Breakout Garden / Grove plank

[Funcan]

Is there a plank for these i2c connectors? Should be dead simple 4 pins (could add SAO and tildagon hexpansion too for a few more)

If somebody hasn’t already covered it, I can fire up kicad I guess

[kd7eir]

This is the first I’ve heard of a desire for such a plank.

[Funcan]

I’ve a small pile of breakout boards with either grove or quiik 4 pin connectors on them - I can connect to them with jumpers but a plank would be faster.

I’ll put something together this week

[kd7eir]

I’m definitely interested. I have several Qwicc/Stemma QT adapter boards for my Raspberry Pi collection.

[ian]

Great idea. I’d be happy to make one up. What are all the connectors types?

[kd7eir]

Adafruit STEMMA & STEMMA QT

Breakout Garden for Raspberry Pi (I2C + SPI)

Stemma, Qwiic and Grove Connectors: Which is Right for You?

[ian]

System	Type	Pitch	Pins	Pin order
Stemma-3	JST PH	2.0mm	3	1.GND, VCC, DAT
Stemma I2C	JST PH	2.0mm	4	1.GND, VCC, SDA, SCL
Qwiic/Stemma QT	JST SH	1.0mm	4	1.GND, VCC, SDA, SCL
Grove	HY2.0/A2008WR-S-4P	2.0mm	4	1.GND, VCC, SDA, SCL
Gravity	JST PH	2.0mm	4	1.SDA, SCL, GND, VCC
Breakout Garden	Edgeboard card connector	2.54mm	5	1.VCC, SDA, SCL, N/A, GND

Does this seem right?

[ian]

Included the STEMMA 3 on a pin with PWM and FREQ measurement. But if it is intended to be used with RGB LEDs, then IO0 is probably a better choice.

Should there be more than one connector for the popular standard like Qwiic/StemmaQT?

The breakout garden is a PCB edge connector. I’ll need to make a footprint for it.

[ian]

With 5 Qwiic connectors.

[kd7eir]

The 5 Qwiic version is excellent, but what about reducing the Qwiic numbers by 1 or 2 and adding an extra Grove connector?

[henrygab]

I’ll share my thoughts, respond to your questions, and also list some additional actionable feedback:

Non-actionable feedback

In case you waffle on inclusion of something, here’s my thoughts.

• GROVE – Glad to see it there for completeness
  • IIRC, I only have a couple boards with Grove. I was unhappy with the custom connector that was almost, but not quite, a standard plug.
• QWIIC – I had one (maybe two) boards with this early on. I switched focus to STEMMA boards because it’s too easy for me to release the magic smoke by send 5V by accident.
• STEMMA / STEMMA QT – My favored standard, primarily because to be called STEMMA, the board must be 5V tolerant (3V3..5V).
  • STEMMA QT boards are my primary quick-connect option for prototyping.
  • I also have a few of the larger STEMMA boards.
  • Neither STEMMA connector has any quick-release, so ensuring a little finger space around each port is likely appreciated.
  • STEMMA QT boards often have a daisy-chain option … so port count is less critical.
• Breakout Garden – This is a new one for me. Is this a popular format? I’m fascinated that card-edge remains a popular connector type. If popular, then I’m glad to see it on here.

Response

I’d appreciate feedback on

1. Should there be multiple of the common connector (Qwiic)
2. Worth including the Stemma 3P connector?

Yes, I would have multiple STEMMA QT (Qwiic) connectors. Many STEMMA QT boards have daisy-chain ports, but not all. Maybe reduce to three (or four) ports, to make it more finger-friendly? I imagine I’d have trouble getting all four connectors populated.

I’m abivalent about the STEMMA 3P connector. If it’s included, I’d give it a unique plank IO … not overload with SDA (IO0) / SCL (IO1). It’s useful for buttons and directly driven (PWM) LEDs, but … the value of a standard port is lower than for I2C.

Questions on the GRAVITY port

• Gravity – Not sure I’m following this one…
  • IIRC, the controller is supposed to use color-coded 0.1" male headers, while the target devices use a connector as shown on the board.
    • Did they update Gravity to have a standard 4-pin connector on the controlling MCU side also?
  • Is the intent of the breakout to emulate a Gravity device?
    • If intended for emulation, maybe have it use a unique pair of plank ports … maybe IO6 and IO7?
  • If not intended for emulating a Gravity device, and they didn’t update the controller side to use similar connector, then I’m not sure I understand this port’s purpose.

[kd7eir]

Thank you for sharing your knowledge with us. I concur with all of your points. I’ve definitely learned something from your reply!

[ian]

Thank you both very much!

Grove

The Grove connector standard, oldest of them all, is now somewhat of a black sheep among the I2C connector ecosystems, and is here half as a piece of history, half as a cautionary tale. Contrary to principles of open-source ecosystems, Grove uses a proprietary connector, which has makers scramble for its proper identification as they try to find a source that is not SeeedStudio. Unlike all the other standards listed here, when you see a 4-pin Grove connector, you don’t know if it’s for I2C, UART, two digital GPIOs or something analog, which ruins the whole “plug and play” idea.

To those of you unfortunate to have to interface with Grove…

This Hack a Day article and the Tom’s Hardware article above left With the impression that Grove was an unloved platform that people are “forced” to work with Do you have Grove boards?

The Grove connector is indeed a weird one, and it took a while to find a compatible part. I don’t have a supplier quote yeet, but the cost at SZLCSC is more than all the other connectors on the board combined. To be fair, that’s not hard as the JST compatible stuff is dirt cheap…

If there’s a lot of Grove stuff out there, then absolutely we should add a second connector. I should probably poll on social media to see what folks have around.

Breakout Garden

@henrygab

Breakout Garden – This is a new one for me. Is this a popular format? I’m fascinated that card-edge remains a popular connector type. If popular, then I’m glad to see it on here.

It seems to be Pimoroni’s thing, and they’re pretty big. I may also be angling a bit to get the Bus Pirate in their webshop

I also like the card edge connectors, and have tried to find a use for them for years. I have one of these, which uses IPS displays on edge connectors to make a nixie-looking thing.

Gravity

f you’ve ever worked with DFRobot parts, you might’ve seen JST-PH 4-pin (or 3-pin) connectors on their boards, too – they’re from their ecosystem called Gravity. Puzzlingly enough, Adafruit claims that STEMMA is compatible with Gravity, apart from their non-I2C devices – since Gravity does the same thing that Grove does, where a 4-pin connector doesn’t guarantee I2C. However, checking the pinout for Gravity I2C devices, it seems that every single pin is in a different spot, in particular, ground and power being reversed. Just like STEMMA, they use 3-pin connectors for digital and analog devices. The fun part is, they also managed to change the pinout for those at some point, also reversing the power pin polarity – while still using the same connector, a no-no for connector standards. Proceed with caution!

Gravity seems like a bit of a mess. If I hadn’t seen so many DF Robot breakouts all over the world, I would not even consider it. Their breakouts are all over though: Aliexpress, EU, Asia, Australia, South America. The only place I don’t see them is in the US, probably because SparkFun and Adafruit dominate the US market.

Stemma 3

My thought here was completeness. You get every possible standard. Originally I had the data connected to IO3, separate from the I2C pins. However, it seems like one really common use is RBG LED strips, which are currently supported on IO0.

I could see removing it to make an I2C only board. On the other hand for the price of the 3P connector (almost free) we support a wider ecosystem of breakouts.

Going Further

Thank you both so much for your feedback, more is still welcome I am just now learning about the quick connect offerings, and have never used one myself. It really is super valuable to hear your thoughts.

• Reduce the number of Qwiic (or increase the space between them)
• Perhaps a second Grove and Stemma I2C
• What is up with Gravity and should it be included
• Stemma 3P - should a non-I2C connector be included?

[kd7eir]

Unfortunately, I have many Grove boards, so my desire for a Grove connector will be very biased.

I have never heard of Gravity before, which is unsurprising since I’ve never ordered from DFRobot.

I do think Stemma 3P would be beneficial, but again, I’m biased.

[ian]

• Stemma 3 stays.
• Reduced the number of Qwiic connectors and gave them some more space.

We can change the board size of course, and I’ll try to add a second Grove connector. First, I want to get the actual footprint for the Breakout Garden connector made because it is going to be MUCH larger than the placeholder 2x5 header currently on the board

I will had this off to the board router for a first draft.

[henrygab]

before you send the board out … I just wanted to check that you had the I2C pullup resistor somewhere? (The only resistor I see is for the LED indicating the board is powered.)

If desiring multiple options for the pullups, maybe a jumper to select between 4k7, none, and an unpopulated resistor?

Given my significant gaps in EE knowledge, I don’t know what the “right” value would be, only that the signal looked terrible on my scope when I didn’t have a pullup resistor…

[ian]

My thinking is that the bus pirate has pull ups and also most breakout boards have pull ups as well.

@henrygab

only that the signal looked terrible on my scope when I didn’t have a pullup resistor…

I bet. I2C used open collector pins. They switch from input to ground, without that pull up your bus just isn’t powered at all. The scope would show floating, and then ground when the pins output low.

[ian]

I think it turned out really nice. I sent the boards in, and I bought parts to have 5 assembled. I’d really like to send one to everyone in the thread - you have some of the cables to test if the socket is correct, I have none of them

[kd7eir]

I have cables for each connector - I picked up a Gravity cable just for this.

[ian]

Excellent! Thank you so much!