A user's guide to i2c


This definitely helps thanks for this!



Just wanted to say thanks to @okyeron, @scanner_darkly and @justmat for putting this together. Thanks!!!



Just a couple questions I hope someone can clarify.

So currently the only way to connect the 16n i2c trs cable to Teletype is the Telexb module?
Is this the same way you would connect the 16n to Er-301?

Example setup:
Teletype backpack -> er301
Teletype backpack -> telexb -> 16n
Teletype backpack -> ansible

With this setup I would be able to use teletype as leader to read the faders on 16n and then control both the er-301 and anisble with an appropriate script?

follow up question:
Since the telexb is powered and has multiple connections, is the teletype backpack necessary? Would teletype still be leader if all the i2c device plug directly to telexb?

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Yes, the i2c network doesn’t care about the configuration, so long as all SDA, SDL, and GND are connected.

No, the TT backpack isn’t necessary. You could connect everything to the TXb, provided the TXb is powered.



Thanks man! Everything I wanted to know! Now if only I could get my hands on a TXb
@bpcmusic do you have timeframe of when Telexb will become available?

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Sales open up tomorrow!



Oh damn! Just in time! That’s two for two @Justmat
I really appreciate the helpful reply’s!

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Was it ever determined if the Slashes board would work as a powered bus? Can I damage anything by trying it?



from the slashes page you linked to:

Additionally, it’s recommended you install a few components to provide pull-up resistance for the i2c connection. Indeed this is necessary if you only plan to use W/-to-W/ communication. If you already have a powered Teletype busboard providing the i2c connection to slashes, then pull-up components are not necessary. Otherwise, you should install them. NB: Any values between 2k2 and 4k99 are suitable for the pull-up resistors.

So yes - in theory it should work as a powered busboard if you populate the 3.3v regulator and the pulls-ups.

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Hi I’m hoping someone can help
I have a Teletype with a w/ and a just friends module connected via I2c
I ordered a txb because I couldn’t find a back pack
How do I connect teletype with txb
Does it automatically pass I2c over the bus board if both are powered from same bus
Sorry and thanks



no, for all i2c devices you always have to connect SDA to SDA, SCL to SCL and GND to GND. these pins will be present on all devices that support i2c. then you connect them with cables.

with your set up you likely don’t even need a TXb as it should work fine with a teletype and 2 devices.

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Yes I understand the I2c connection part of it
I’ve made a few wires was easy enough
I’m trying to picture how it connects to teletype
Same way? I2c



txb? yes, it has i2c pins on the back.

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Ok Thanks it seems like your really trying to help me
I plan to use …1 teletype ,2w/s mounted to a slash board,
1 just friends, 1 txo, 1 txi and 1 txb also whatever else I can connect in the future …er-301…
How do I connect this?
Power from bus board to teletype and power from bus to txb?
Where do the I2c cables go ?
To the teletype or the txb?



in my setup, I have just one longish I2C cable with multiple headers and all of my I2C modules are connected to this very same cable. If you don’t have such a cable, just daisy chain all of them together.

the 10-pin power cables for each module should connect as usual to your power supply—I2C is not a substitute for powering a module.



So maybe this will help?

At the left a eurorack power cable attaches to a TeleType-backpack (which gives power to the TT). Then there are smaller i2c cables connected from the backpack to various modules. At the far right the Telex’s are daisy-chained to each other.

As others have said - i2c is completely separate from the eurorack power bus.

EDIT - I’ve also just updated the “how do i connect everything?” section above - please re-read that section and let us know if you have specific questions.



i just want to reiterate that most of the questions have already been answered in the guide. if something in the guide is not clear please post a specific quote so we can fix the guide.



When making an i2c-capable device using a microcontroller (say, Teensy 3.x), how does one format i2c messages to work with other devices? Does it require specific formatting based on what will be the “follower,” or is it configurable in the device (ex. er-301)? I see that addressing is done in firmware, but I’m wondering how different channels are configured, etc. Is there a guide for this, too? Or is it more of a consensus among developers?

Trying to put together a new controller device and wondering how best to make it i2c capable. Thank you!!



relevant thread: Teletype I2C protocol

and check out https://github.com/scanner-darkly/teletype/wiki/II-protocol - this has exactly the info you’re looking for!

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Wonderful, thank you!

Also just found this: Using I2C protocol in new hardware designs