possible to mix stemma 3-pin and stemma qt?

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rxb
 
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Joined: Mon May 30, 2022 11:15 pm

possible to mix stemma 3-pin and stemma qt?

Post by rxb »

Hi, I'm just getting started with a new project and I'd like to try using the stemma ecosystem for the first time. The project requires a relay, and I've found this Stemma 3-pin relay here:

https://www.adafruit.com/product/4409

I was planning to use an ESP32 based board, since I've used those before. This board has a Stemma qt connector:

https://www.adafruit.com/product/5405

But I'm stuck trying to figure out how or even if it's possible to connect Stemma Qt to Stemma 3-pin? I've seen the adapters between 4-pin Stemma and QT as they are both 4-pin connectors and this makes sense.

Am I thinking about this the wrong way? Thanks so much for your help.

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dastels
 
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Joined: Tue Oct 20, 2015 3:22 pm

Re: possible to mix stemma 3-pin and stemma qt?

Post by dastels »

4-pin STEMMA and STEMMA-QT are typically (as Adafruit uses them) I2C connections: V+, gnd, SDA, and SCL. 3-Pin JST/STEMMA includes V+, gnd, and a single digital or analog connection (depending on how it's connected and what it's connected to). You can probably use one of the I2C pins as a digital output, but then you loose the ability to use I2C.

If you use a QTPY ESP32-S2 (https://www.adafruit.com/product/5325) the STEMMA-QT port uses different SDA/SCL that the edge connector so you could retain I2C capability.

As far as the physical connection goes, you'll need to make something yourself. You could use https://www.adafruit.com/product/4528 and https://www.adafruit.com/product/3894, replacing the larger 4-pin connector housing on the STEMMA-QT cable with the 3-pin connector housing (using the data connection you choose (SDA or SCL).

Dave

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