A user's guide to i2c

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.

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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!!

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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

All great information I totally understand
Thank you
But Can I try this for a question instead ?
I do not have a backpack
I believe I read I could use the txb instead of the backpack

Yes, you could. I2c does not care about the configuration of the modules. In your case you would just connect the teletype i2c pins to the txb. then as long as all the other modules are connected to txb it will work.


Perfect Got it thanks

This is probably stupid but without a TT is there anything I can do with i2c?

I have Ansible, JF, w/, and tetrapad…

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Yeah, check out polyearthsea for your Ansible. You’d need a powered I2C bus but it would let you use synthesis mode on JF.


Thanks! Another stupid question, what do you recommend for a powered bus?

I don’t build anything yet…

There are several options for powered busboards listed in the guide at the top of this thread.


Sorry if I’m being dense. I couldn’t determine from the guide above how daisy chaining works. I’m assuming this –

From TT I’m going SCL-SCL (etc) to 3 pins on ansible. From the other 3 pins I’m connecting SCL-SCL (etc) to JF. Does that sound/look right?

Also, should the new TT (black PCB) be able to handle an ansible, JF, and TXO+ without a backpack? Thanks!


that looks right to me